[10/14] KVM: x86: Make Hyper-V emulation optional

  Hyper-V emulation in KVM is a fairly big chunk and in some cases it may be
desirable to not compile it in to reduce module sizes as well as the attack
surface. Introduce CONFIG_KVM_HYPERV option to make it possible.

Note, there's room for further nVMX/nSVM code optimizations when
!CONFIG_KVM_HYPERV, this will be done in follow-up patches.

Reorganize Makefile a bit so all CONFIG_HYPERV and CONFIG_KVM_HYPERV files
are grouped together.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/include/asm/kvm_host.h |  4 +++
 arch/x86/kvm/Kconfig            | 14 ++++++++
 arch/x86/kvm/Makefile           | 23 ++++++------
 arch/x86/kvm/cpuid.c            |  6 ++++
 arch/x86/kvm/hyperv.h           | 30 ++++++++++++++--
 arch/x86/kvm/irq_comm.c         |  9 ++++-
 arch/x86/kvm/svm/hyperv.h       |  7 ++++
 arch/x86/kvm/vmx/hyperv.h       |  8 +++++
 arch/x86/kvm/vmx/nested.c       | 15 ++++++++
 arch/x86/kvm/x86.c              | 62 ++++++++++++++++++++++++---------
 10 files changed, 147 insertions(+), 31 deletions(-)
  

On Wed, 2023-10-25 at 17:24 +0200, Vitaly Kuznetsov wrote:
> Hyper-V emulation in KVM is a fairly big chunk and in some cases it may be
> desirable to not compile it in to reduce module sizes as well as the attack
> surface. Introduce CONFIG_KVM_HYPERV option to make it possible.
> 
> Note, there's room for further nVMX/nSVM code optimizations when
> !CONFIG_KVM_HYPERV, this will be done in follow-up patches.
> 
> Reorganize Makefile a bit so all CONFIG_HYPERV and CONFIG_KVM_HYPERV files
> are grouped together.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/include/asm/kvm_host.h |  4 +++
>  arch/x86/kvm/Kconfig            | 14 ++++++++
>  arch/x86/kvm/Makefile           | 23 ++++++------
>  arch/x86/kvm/cpuid.c            |  6 ++++
>  arch/x86/kvm/hyperv.h           | 30 ++++++++++++++--
>  arch/x86/kvm/irq_comm.c         |  9 ++++-
>  arch/x86/kvm/svm/hyperv.h       |  7 ++++
>  arch/x86/kvm/vmx/hyperv.h       |  8 +++++
>  arch/x86/kvm/vmx/nested.c       | 15 ++++++++
>  arch/x86/kvm/x86.c              | 62 ++++++++++++++++++++++++---------
>  10 files changed, 147 insertions(+), 31 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 7fb2810f4573..e5b881dda747 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1095,6 +1095,7 @@ enum hv_tsc_page_status {
>  	HV_TSC_PAGE_BROKEN,
>  };
>  
> +#ifdef CONFIG_KVM_HYPERV
>  /* Hyper-V emulation context */
>  struct kvm_hv {
>  	struct mutex hv_lock;
> @@ -1127,6 +1128,7 @@ struct kvm_hv {
>  
>  	struct kvm_hv_syndbg hv_syndbg;
>  };
> +#endif
>  
>  struct msr_bitmap_range {
>  	u32 flags;
> @@ -1349,7 +1351,9 @@ struct kvm_arch {
>  	/* reads protected by irq_srcu, writes by irq_lock */
>  	struct hlist_head mask_notifier_list;
>  
> +#ifdef CONFIG_KVM_HYPERV
>  	struct kvm_hv hyperv;
> +#endif
>  
>  #ifdef CONFIG_KVM_XEN
>  	struct kvm_xen xen;
> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
> index 950c12868d30..93930cef9b3b 100644
> --- a/arch/x86/kvm/Kconfig
> +++ b/arch/x86/kvm/Kconfig
> @@ -129,6 +129,20 @@ config KVM_SMM
>  
>  	  If unsure, say Y.
>  
> +config KVM_HYPERV
> +	bool "Support for Microsoft Hyper-V emulation"
> +	depends on KVM
> +	default y
> +	help
> +	  Provides KVM support for emulating Microsoft Hyper-V.  This allows KVM
> +	  to expose a subset of the paravirtualized interfaces defined in the
> +	  Hyper-V Hypervisor Top-Level Functional Specification (TLFS):
> +	  https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
> +	  These interfaces are required for the correct and performant functioning
> +	  of Windows and Hyper-V guests on KVM.
Looks very good.

> +
> +	  If unsure, say "Y".
> +
>  config KVM_XEN
>  	bool "Support for Xen hypercall interface"
>  	depends on KVM
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index 8ea872401cd6..b97b875ad75f 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -11,32 +11,33 @@ include $(srctree)/virt/kvm/Makefile.kvm
>  
>  kvm-y			+= x86.o emulate.o i8259.o irq.o lapic.o \
>  			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
> -			   hyperv.o debugfs.o mmu/mmu.o mmu/page_track.o \
> +			   debugfs.o mmu/mmu.o mmu/page_track.o \
>  			   mmu/spte.o
>  
> -ifdef CONFIG_HYPERV
> -kvm-y			+= kvm_onhyperv.o
> -endif
> -
>  kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
> +kvm-$(CONFIG_KVM_HYPERV) += hyperv.o
>  kvm-$(CONFIG_KVM_XEN)	+= xen.o
>  kvm-$(CONFIG_KVM_SMM)	+= smm.o
>  
>  kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
> -			   vmx/hyperv.o vmx/hyperv_evmcs.o vmx/nested.o vmx/posted_intr.o
> -kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
> +			   vmx/nested.o vmx/posted_intr.o
>  
> -ifdef CONFIG_HYPERV
> -kvm-intel-y		+= vmx/vmx_onhyperv.o
> -endif
> +kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
>  
>  kvm-amd-y		+= svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o \
> -			   svm/sev.o svm/hyperv.o
> +			   svm/sev.o
>  
>  ifdef CONFIG_HYPERV
> +kvm-y			+= kvm_onhyperv.o
> +kvm-intel-y		+= vmx/vmx_onhyperv.o vmx/hyperv_evmcs.o
>  kvm-amd-y		+= svm/svm_onhyperv.o
>  endif
>  
> +ifdef CONFIG_KVM_HYPERV
> +kvm-intel-y		+= vmx/hyperv.o vmx/hyperv_evmcs.o
> +kvm-amd-y		+= svm/hyperv.o
> +endif
> +
>  obj-$(CONFIG_KVM)	+= kvm.o
>  obj-$(CONFIG_KVM_INTEL)	+= kvm-intel.o
>  obj-$(CONFIG_KVM_AMD)	+= kvm-amd.o

This also looks much better.

> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 464b23ac5f93..da8e0873f63a 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -314,11 +314,15 @@ EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
>  
>  static bool kvm_cpuid_has_hyperv(struct kvm_cpuid_entry2 *entries, int nent)
>  {
> +#ifdef CONFIG_KVM_HYPERV
>  	struct kvm_cpuid_entry2 *entry;
>  
>  	entry = cpuid_entry2_find(entries, nent, HYPERV_CPUID_INTERFACE,
>  				  KVM_CPUID_INDEX_NOT_SIGNIFICANT);
>  	return entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX;
> +#else
> +	return false;
> +#endif
>  }
>  
>  static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> @@ -433,11 +437,13 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
>  		return 0;
>  	}
>  
> +#ifdef CONFIG_KVM_HYPERV
>  	if (kvm_cpuid_has_hyperv(e2, nent)) {
>  		r = kvm_hv_vcpu_init(vcpu);
>  		if (r)
>  			return r;
>  	}
> +#endif
>  
>  	r = kvm_check_cpuid(vcpu, e2, nent);
>  	if (r)
> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
> index 75dcbe598fbc..5c5ec7015136 100644
> --- a/arch/x86/kvm/hyperv.h
> +++ b/arch/x86/kvm/hyperv.h
> @@ -24,6 +24,8 @@
>  #include <linux/kvm_host.h>
>  #include "x86.h"
>  
> +#ifdef CONFIG_KVM_HYPERV
> +
>  /* "Hv#1" signature */
>  #define HYPERV_CPUID_SIGNATURE_EAX 0x31237648
>  
> @@ -259,5 +261,29 @@ static inline void kvm_hv_nested_transtion_tlb_flush(struct kvm_vcpu *vcpu, bool
>  }
>  
>  int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
> -
> -#endif
> +#else /* CONFIG_KVM_HYPERV */
> +static inline void kvm_hv_setup_tsc_page(struct kvm *kvm,
> +					 struct pvclock_vcpu_time_info *hv_clock) {}
> +static inline void kvm_hv_request_tsc_page_update(struct kvm *kvm) {}
> +static inline void kvm_hv_init_vm(struct kvm *kvm) {}
> +static inline void kvm_hv_destroy_vm(struct kvm *kvm) {}
> +static inline int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu) { return 0; }
> +static inline void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu) {}
> +static inline bool kvm_hv_hypercall_enabled(struct kvm_vcpu *vcpu) { return false; }
> +static inline int kvm_hv_hypercall(struct kvm_vcpu *vcpu) { return HV_STATUS_ACCESS_DENIED; }
> +static inline void kvm_hv_vcpu_purge_flush_tlb(struct kvm_vcpu *vcpu) {}
> +static inline void kvm_hv_free_pa_page(struct kvm *kvm) {}
> +static inline bool kvm_hv_synic_has_vector(struct kvm_vcpu *vcpu, int vector) { return false; }
> +static inline bool kvm_hv_synic_auto_eoi_set(struct kvm_vcpu *vcpu, int vector) { return false; }
> +static inline void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector) {}
> +static inline bool kvm_hv_invtsc_suppressed(struct kvm_vcpu *vcpu) { return false; }
> +static inline void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu, bool hyperv_enabled) {}
> +static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu) { return false; }
> +static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu) { return false; }
> +static inline bool guest_hv_cpuid_has_l2_tlb_flush(struct kvm_vcpu *vcpu) { return false; }
> +static inline int kvm_hv_verify_vp_assist(struct kvm_vcpu *vcpu) { return 0; }
> +static inline u32 kvm_hv_get_vpindex(struct kvm_vcpu *vcpu) { return vcpu->vcpu_idx; }
> +static inline void kvm_hv_nested_transtion_tlb_flush(struct kvm_vcpu *vcpu, bool tdp_enabled) {}
> +#endif /* CONFIG_KVM_HYPERV */
> +
> +#endif /* __ARCH_X86_KVM_HYPERV_H__ */


> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
> index 16d076a1b91a..68f3f6c26046 100644
> --- a/arch/x86/kvm/irq_comm.c
> +++ b/arch/x86/kvm/irq_comm.c
> @@ -144,7 +144,7 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
>  	return kvm_irq_delivery_to_apic(kvm, NULL, &irq, NULL);
>  }
>  
> -
> +#ifdef CONFIG_KVM_HYPERV
>  static int kvm_hv_set_sint(struct kvm_kernel_irq_routing_entry *e,
>  		    struct kvm *kvm, int irq_source_id, int level,
>  		    bool line_status)
> @@ -154,6 +154,7 @@ static int kvm_hv_set_sint(struct kvm_kernel_irq_routing_entry *e,
>  
>  	return kvm_hv_synic_set_irq(kvm, e->hv_sint.vcpu, e->hv_sint.sint);
>  }
> +#endif
>  
>  int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
>  			      struct kvm *kvm, int irq_source_id, int level,
> @@ -163,9 +164,11 @@ int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
>  	int r;
>  
>  	switch (e->type) {
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_IRQ_ROUTING_HV_SINT:
>  		return kvm_hv_set_sint(e, kvm, irq_source_id, level,
>  				       line_status);
> +#endif
>  
>  	case KVM_IRQ_ROUTING_MSI:
>  		if (kvm_msi_route_invalid(kvm, e))
> @@ -314,11 +317,13 @@ int kvm_set_routing_entry(struct kvm *kvm,
>  		if (kvm_msi_route_invalid(kvm, e))
>  			return -EINVAL;
>  		break;
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_IRQ_ROUTING_HV_SINT:
>  		e->set = kvm_hv_set_sint;
>  		e->hv_sint.vcpu = ue->u.hv_sint.vcpu;
>  		e->hv_sint.sint = ue->u.hv_sint.sint;
>  		break;
> +#endif
>  #ifdef CONFIG_KVM_XEN
>  	case KVM_IRQ_ROUTING_XEN_EVTCHN:
>  		return kvm_xen_setup_evtchn(kvm, e, ue);
> @@ -438,5 +443,7 @@ void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu,
>  
>  void kvm_arch_irq_routing_update(struct kvm *kvm)
>  {
> +#ifdef CONFIG_KVM_HYPERV
>  	kvm_hv_irq_routing_update(kvm);
> +#endif
>  }
> diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h
> index 02f4784b5d44..14eec2d9b6be 100644
> --- a/arch/x86/kvm/svm/hyperv.h
> +++ b/arch/x86/kvm/svm/hyperv.h
> @@ -11,6 +11,7 @@
>  #include "../hyperv.h"
>  #include "svm.h"
>  
> +#ifdef CONFIG_KVM_HYPERV
>  static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_svm *svm = to_svm(vcpu);
> @@ -41,5 +42,11 @@ static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
>  }
>  
>  void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
> +#else /* CONFIG_KVM_HYPERV */
> +static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu) {}
> +static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu) { return false; }
> +static inline void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu) {}
> +#endif /* CONFIG_KVM_HYPERV */
> +
>  
>  #endif /* __ARCH_X86_KVM_SVM_HYPERV_H__ */
> diff --git a/arch/x86/kvm/vmx/hyperv.h b/arch/x86/kvm/vmx/hyperv.h
> index d4ed99008518..933ef6cad5e6 100644
> --- a/arch/x86/kvm/vmx/hyperv.h
> +++ b/arch/x86/kvm/vmx/hyperv.h
> @@ -20,6 +20,7 @@ enum nested_evmptrld_status {
>  	EVMPTRLD_ERROR,
>  };
>  
> +#ifdef CONFIG_KVM_HYPERV
>  u64 nested_get_evmptr(struct kvm_vcpu *vcpu);
>  uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu);
>  int nested_enable_evmcs(struct kvm_vcpu *vcpu,
> @@ -28,5 +29,12 @@ void nested_evmcs_filter_control_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *
>  int nested_evmcs_check_controls(struct vmcs12 *vmcs12);
>  bool nested_evmcs_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu);
>  void vmx_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
> +#else
> +static inline u64 nested_get_evmptr(struct kvm_vcpu *vcpu) { return EVMPTR_INVALID; }
> +static inline void nested_evmcs_filter_control_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata) {}
> +static inline bool nested_evmcs_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu) { return false; }
> +static inline int nested_evmcs_check_controls(struct vmcs12 *vmcs12) { return 0; }
> +#endif
> +
>  
>  #endif /* __KVM_X86_VMX_HYPERV_H */
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 382c0746d069..d0d735974b2c 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -226,6 +226,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx)
>  
>  static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
>  {
> +#ifdef CONFIG_KVM_HYPERV
>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>  
> @@ -241,6 +242,7 @@ static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
>  		hv_vcpu->nested.vm_id = 0;
>  		hv_vcpu->nested.vp_id = 0;
>  	}
> +#endif
>  }
>  
>  static void vmx_sync_vmcs_host_state(struct vcpu_vmx *vmx,
> @@ -1570,6 +1572,7 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx)
>  	vmcs_load(vmx->loaded_vmcs->vmcs);
>  }
>  
> +#ifdef CONFIG_KVM_HYPERV
>  static void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields)
>  {
>  	struct vmcs12 *vmcs12 = vmx->nested.cached_vmcs12;
> @@ -2077,6 +2080,10 @@ static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
>  
>  	return EVMPTRLD_SUCCEEDED;
>  }
> +#else /* CONFIG_KVM_HYPERV */
> +static inline void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields) {}
> +static inline void copy_vmcs12_to_enlightened(struct vcpu_vmx *vmx) {}
> +#endif /* CONFIG_KVM_HYPERV */
>  
>  void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
>  {
> @@ -3155,6 +3162,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_KVM_HYPERV
>  static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -3182,6 +3190,9 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
>  
>  	return true;
>  }
> +#else
> +static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu) { return true; }
> +#endif
>  
>  static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
>  {
> @@ -3552,11 +3563,13 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>  	if (!nested_vmx_check_permission(vcpu))
>  		return 1;
>  
> +#ifdef CONFIG_KVM_HYPERV
>  	evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
>  	if (evmptrld_status == EVMPTRLD_ERROR) {
>  		kvm_queue_exception(vcpu, UD_VECTOR);
>  		return 1;
>  	}
> +#endif
>  
>  	kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
>  
> @@ -7090,7 +7103,9 @@ struct kvm_x86_nested_ops vmx_nested_ops = {
>  	.set_state = vmx_set_nested_state,
>  	.get_nested_state_pages = vmx_get_nested_state_pages,
>  	.write_log_dirty = nested_vmx_write_pml_buffer,
> +#ifdef CONFIG_KVM_HYPERV
>  	.enable_evmcs = nested_enable_evmcs,
>  	.get_evmcs_version = nested_get_evmcs_version,
>  	.hv_inject_synthetic_vmexit_post_tlb_flush = vmx_hv_inject_synthetic_vmexit_post_tlb_flush,
> +#endif
>  };
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index cc2524598368..8ef9898092cd 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1504,6 +1504,8 @@ static unsigned num_msrs_to_save;
>  static const u32 emulated_msrs_all[] = {
>  	MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
>  	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
> +
> +#ifdef CONFIG_KVM_HYPERV
>  	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
>  	HV_X64_MSR_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,
>  	HV_X64_MSR_TSC_FREQUENCY, HV_X64_MSR_APIC_FREQUENCY,
> @@ -1521,6 +1523,7 @@ static const u32 emulated_msrs_all[] = {
>  	HV_X64_MSR_SYNDBG_CONTROL, HV_X64_MSR_SYNDBG_STATUS,
>  	HV_X64_MSR_SYNDBG_SEND_BUFFER, HV_X64_MSR_SYNDBG_RECV_BUFFER,
>  	HV_X64_MSR_SYNDBG_PENDING_BUFFER,
> +#endif
>  
>  	MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
>  	MSR_KVM_PV_EOI_EN, MSR_KVM_ASYNC_PF_INT, MSR_KVM_ASYNC_PF_ACK,
> @@ -4022,6 +4025,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		 * the need to ignore the workaround.
>  		 */
>  		break;
> +#ifdef CONFIG_KVM_HYPERV
>  	case HV_X64_MSR_GUEST_OS_ID ... HV_X64_MSR_SINT15:
>  	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
>  	case HV_X64_MSR_SYNDBG_OPTIONS:
> @@ -4034,6 +4038,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case HV_X64_MSR_TSC_INVARIANT_CONTROL:
>  		return kvm_hv_set_msr_common(vcpu, msr, data,
>  					     msr_info->host_initiated);
> +#endif
>  	case MSR_IA32_BBL_CR_CTL3:
>  		/* Drop writes to this legacy MSR -- see rdmsr
>  		 * counterpart for further detail.
> @@ -4378,6 +4383,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		 */
>  		msr_info->data = 0x20000000;
>  		break;
> +#ifdef CONFIG_KVM_HYPERV
>  	case HV_X64_MSR_GUEST_OS_ID ... HV_X64_MSR_SINT15:
>  	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
>  	case HV_X64_MSR_SYNDBG_OPTIONS:
> @@ -4391,6 +4397,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		return kvm_hv_get_msr_common(vcpu,
>  					     msr_info->index, &msr_info->data,
>  					     msr_info->host_initiated);
> +#endif
>  	case MSR_IA32_BBL_CR_CTL3:
>  		/* This legacy MSR exists but isn't fully documented in current
>  		 * silicon.  It is however accessed by winxp in very narrow
> @@ -4528,6 +4535,7 @@ static inline bool kvm_can_mwait_in_guest(void)
>  		boot_cpu_has(X86_FEATURE_ARAT);
>  }
>  
> +#ifdef CONFIG_KVM_HYPERV
>  static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
>  					    struct kvm_cpuid2 __user *cpuid_arg)
>  {
> @@ -4548,6 +4556,7 @@ static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
>  
>  	return 0;
>  }
> +#endif
>  
>  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  {
> @@ -4574,9 +4583,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_PIT_STATE2:
>  	case KVM_CAP_SET_IDENTITY_MAP_ADDR:
>  	case KVM_CAP_VCPU_EVENTS:
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_CAP_HYPERV:
>  	case KVM_CAP_HYPERV_VAPIC:
>  	case KVM_CAP_HYPERV_SPIN:
> +	case KVM_CAP_HYPERV_TIME:
>  	case KVM_CAP_HYPERV_SYNIC:
>  	case KVM_CAP_HYPERV_SYNIC2:
>  	case KVM_CAP_HYPERV_VP_INDEX:
> @@ -4586,6 +4597,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_HYPERV_CPUID:
>  	case KVM_CAP_HYPERV_ENFORCE_CPUID:
>  	case KVM_CAP_SYS_HYPERV_CPUID:
> +#endif
>  	case KVM_CAP_PCI_SEGMENT:
>  	case KVM_CAP_DEBUGREGS:
>  	case KVM_CAP_X86_ROBUST_SINGLESTEP:
> @@ -4595,7 +4607,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  	case KVM_CAP_GET_TSC_KHZ:
>  	case KVM_CAP_KVMCLOCK_CTRL:
>  	case KVM_CAP_READONLY_MEM:
> -	case KVM_CAP_HYPERV_TIME:
>  	case KVM_CAP_IOAPIC_POLARITY_IGNORED:
>  	case KVM_CAP_TSC_DEADLINE_TIMER:
>  	case KVM_CAP_DISABLE_QUIRKS:
> @@ -4705,12 +4716,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		r = kvm_x86_ops.nested_ops->get_state ?
>  			kvm_x86_ops.nested_ops->get_state(NULL, NULL, 0) : 0;
>  		break;
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
>  		r = kvm_x86_ops.enable_l2_tlb_flush != NULL;
>  		break;
>  	case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
>  		r = kvm_x86_ops.nested_ops->enable_evmcs != NULL;
>  		break;
> +#endif
>  	case KVM_CAP_SMALLER_MAXPHYADDR:
>  		r = (int) allow_smaller_maxphyaddr;
>  		break;
> @@ -4872,9 +4885,11 @@ long kvm_arch_dev_ioctl(struct file *filp,
>  	case KVM_GET_MSRS:
>  		r = msr_io(NULL, argp, do_get_msr_feature, 1);
>  		break;
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_GET_SUPPORTED_HV_CPUID:
>  		r = kvm_ioctl_get_supported_hv_cpuid(NULL, argp);
>  		break;
> +#endif
>  	case KVM_GET_DEVICE_ATTR: {
>  		struct kvm_device_attr attr;
>  		r = -EFAULT;
> @@ -5700,14 +5715,11 @@ static int kvm_vcpu_ioctl_device_attr(struct kvm_vcpu *vcpu,
>  static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>  				     struct kvm_enable_cap *cap)
>  {
> -	int r;
> -	uint16_t vmcs_version;
> -	void __user *user_ptr;
> -
>  	if (cap->flags)
>  		return -EINVAL;
>  
>  	switch (cap->cap) {
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_CAP_HYPERV_SYNIC2:
>  		if (cap->args[0])
>  			return -EINVAL;
> @@ -5719,16 +5731,22 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>  		return kvm_hv_activate_synic(vcpu, cap->cap ==
>  					     KVM_CAP_HYPERV_SYNIC2);
>  	case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
> -		if (!kvm_x86_ops.nested_ops->enable_evmcs)
> -			return -ENOTTY;
> -		r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, &vmcs_version);
> -		if (!r) {
> -			user_ptr = (void __user *)(uintptr_t)cap->args[0];
> -			if (copy_to_user(user_ptr, &vmcs_version,
> -					 sizeof(vmcs_version)))
> -				r = -EFAULT;
> +		{
> +			int r;
> +			uint16_t vmcs_version;
> +			void __user *user_ptr;
> +
> +			if (!kvm_x86_ops.nested_ops->enable_evmcs)
> +				return -ENOTTY;
> +			r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, &vmcs_version);
> +			if (!r) {
> +				user_ptr = (void __user *)(uintptr_t)cap->args[0];
> +				if (copy_to_user(user_ptr, &vmcs_version,
> +						 sizeof(vmcs_version)))
> +					r = -EFAULT;
> +			}
> +			return r;
>  		}
> -		return r;

Minor nitpick: Unless I missed something the above is just refactoring. Can this be split
into a separate patch?


>  	case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
>  		if (!kvm_x86_ops.enable_l2_tlb_flush)
>  			return -ENOTTY;
> @@ -5737,6 +5755,7 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>  
>  	case KVM_CAP_HYPERV_ENFORCE_CPUID:
>  		return kvm_hv_set_enforce_cpuid(vcpu, cap->args[0]);
> +#endif
>  
>  	case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
>  		vcpu->arch.pv_cpuid.enforce = cap->args[0];
> @@ -6129,9 +6148,11 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>  		srcu_read_unlock(&vcpu->kvm->srcu, idx);
>  		break;
>  	}
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_GET_SUPPORTED_HV_CPUID:
>  		r = kvm_ioctl_get_supported_hv_cpuid(vcpu, argp);
>  		break;
> +#endif
>  #ifdef CONFIG_KVM_XEN
>  	case KVM_XEN_VCPU_GET_ATTR: {
>  		struct kvm_xen_vcpu_attr xva;
> @@ -7189,6 +7210,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>  		r = static_call(kvm_x86_mem_enc_unregister_region)(kvm, &region);
>  		break;
>  	}
> +#ifdef CONFIG_KVM_HYPERV
>  	case KVM_HYPERV_EVENTFD: {
>  		struct kvm_hyperv_eventfd hvevfd;
>  
> @@ -7198,6 +7220,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>  		r = kvm_vm_ioctl_hv_eventfd(kvm, &hvevfd);
>  		break;
>  	}
> +#endif
>  	case KVM_SET_PMU_EVENT_FILTER:
>  		r = kvm_vm_ioctl_set_pmu_event_filter(kvm, argp);
>  		break;
> @@ -10576,19 +10599,20 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>  
>  static void vcpu_load_eoi_exitmap(struct kvm_vcpu *vcpu)
>  {
> -	u64 eoi_exit_bitmap[4];
> -
>  	if (!kvm_apic_hw_enabled(vcpu->arch.apic))
>  		return;
>  
> +#ifdef CONFIG_KVM_HYPERV
>  	if (to_hv_vcpu(vcpu)) {
> +		u64 eoi_exit_bitmap[4];
> +
>  		bitmap_or((ulong *)eoi_exit_bitmap,
>  			  vcpu->arch.ioapic_handled_vectors,
>  			  to_hv_synic(vcpu)->vec_bitmap, 256);
>  		static_call_cond(kvm_x86_load_eoi_exitmap)(vcpu, eoi_exit_bitmap);
>  		return;
>  	}
> -
> +#endif

Same here.

>  	static_call_cond(kvm_x86_load_eoi_exitmap)(
>  		vcpu, (u64 *)vcpu->arch.ioapic_handled_vectors);
>  }
> @@ -10679,9 +10703,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  		 * the flushes are considered "remote" and not "local" because
>  		 * the requests can be initiated from other vCPUs.
>  		 */
> +#ifdef CONFIG_KVM_HYPERV
>  		if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu) &&
>  		    kvm_hv_vcpu_flush_tlb(vcpu))
>  			kvm_vcpu_flush_tlb_guest(vcpu);
> +#endif
>  
>  		if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
>  			vcpu->run->exit_reason = KVM_EXIT_TPR_ACCESS;
> @@ -10734,6 +10760,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  			vcpu_load_eoi_exitmap(vcpu);
>  		if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
>  			kvm_vcpu_reload_apic_access_page(vcpu);
> +#ifdef CONFIG_KVM_HYPERV
>  		if (kvm_check_request(KVM_REQ_HV_CRASH, vcpu)) {
>  			vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
>  			vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH;
> @@ -10764,6 +10791,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>  		 */
>  		if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
>  			kvm_hv_process_stimers(vcpu);
> +#endif
>  		if (kvm_check_request(KVM_REQ_APICV_UPDATE, vcpu))
>  			kvm_vcpu_update_apicv(vcpu);
>  		if (kvm_check_request(KVM_REQ_APF_READY, vcpu))

Besides nitpicks,

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>


Best regards,
	Maxim Levitsky
  

Maxim Levitsky <mlevitsk@redhat.com> writes:

> On Wed, 2023-10-25 at 17:24 +0200, Vitaly Kuznetsov wrote:
>> Hyper-V emulation in KVM is a fairly big chunk and in some cases it may be
>> desirable to not compile it in to reduce module sizes as well as the attack
>> surface. Introduce CONFIG_KVM_HYPERV option to make it possible.
>> 
>> Note, there's room for further nVMX/nSVM code optimizations when
>> !CONFIG_KVM_HYPERV, this will be done in follow-up patches.
>> 
>> Reorganize Makefile a bit so all CONFIG_HYPERV and CONFIG_KVM_HYPERV files
>> are grouped together.
>> 
>> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
>> ---
>>  arch/x86/include/asm/kvm_host.h |  4 +++
>>  arch/x86/kvm/Kconfig            | 14 ++++++++
>>  arch/x86/kvm/Makefile           | 23 ++++++------
>>  arch/x86/kvm/cpuid.c            |  6 ++++
>>  arch/x86/kvm/hyperv.h           | 30 ++++++++++++++--
>>  arch/x86/kvm/irq_comm.c         |  9 ++++-
>>  arch/x86/kvm/svm/hyperv.h       |  7 ++++
>>  arch/x86/kvm/vmx/hyperv.h       |  8 +++++
>>  arch/x86/kvm/vmx/nested.c       | 15 ++++++++
>>  arch/x86/kvm/x86.c              | 62 ++++++++++++++++++++++++---------
>>  10 files changed, 147 insertions(+), 31 deletions(-)
>> 
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 7fb2810f4573..e5b881dda747 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -1095,6 +1095,7 @@ enum hv_tsc_page_status {
>>  	HV_TSC_PAGE_BROKEN,
>>  };
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  /* Hyper-V emulation context */
>>  struct kvm_hv {
>>  	struct mutex hv_lock;
>> @@ -1127,6 +1128,7 @@ struct kvm_hv {
>>  
>>  	struct kvm_hv_syndbg hv_syndbg;
>>  };
>> +#endif
>>  
>>  struct msr_bitmap_range {
>>  	u32 flags;
>> @@ -1349,7 +1351,9 @@ struct kvm_arch {
>>  	/* reads protected by irq_srcu, writes by irq_lock */
>>  	struct hlist_head mask_notifier_list;
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  	struct kvm_hv hyperv;
>> +#endif
>>  
>>  #ifdef CONFIG_KVM_XEN
>>  	struct kvm_xen xen;
>> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
>> index 950c12868d30..93930cef9b3b 100644
>> --- a/arch/x86/kvm/Kconfig
>> +++ b/arch/x86/kvm/Kconfig
>> @@ -129,6 +129,20 @@ config KVM_SMM
>>  
>>  	  If unsure, say Y.
>>  
>> +config KVM_HYPERV
>> +	bool "Support for Microsoft Hyper-V emulation"
>> +	depends on KVM
>> +	default y
>> +	help
>> +	  Provides KVM support for emulating Microsoft Hyper-V.  This allows KVM
>> +	  to expose a subset of the paravirtualized interfaces defined in the
>> +	  Hyper-V Hypervisor Top-Level Functional Specification (TLFS):
>> +	  https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs
>> +	  These interfaces are required for the correct and performant functioning
>> +	  of Windows and Hyper-V guests on KVM.
> Looks very good.
>
>> +
>> +	  If unsure, say "Y".
>> +
>>  config KVM_XEN
>>  	bool "Support for Xen hypercall interface"
>>  	depends on KVM
>> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
>> index 8ea872401cd6..b97b875ad75f 100644
>> --- a/arch/x86/kvm/Makefile
>> +++ b/arch/x86/kvm/Makefile
>> @@ -11,32 +11,33 @@ include $(srctree)/virt/kvm/Makefile.kvm
>>  
>>  kvm-y			+= x86.o emulate.o i8259.o irq.o lapic.o \
>>  			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
>> -			   hyperv.o debugfs.o mmu/mmu.o mmu/page_track.o \
>> +			   debugfs.o mmu/mmu.o mmu/page_track.o \
>>  			   mmu/spte.o
>>  
>> -ifdef CONFIG_HYPERV
>> -kvm-y			+= kvm_onhyperv.o
>> -endif
>> -
>>  kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
>> +kvm-$(CONFIG_KVM_HYPERV) += hyperv.o
>>  kvm-$(CONFIG_KVM_XEN)	+= xen.o
>>  kvm-$(CONFIG_KVM_SMM)	+= smm.o
>>  
>>  kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
>> -			   vmx/hyperv.o vmx/hyperv_evmcs.o vmx/nested.o vmx/posted_intr.o
>> -kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
>> +			   vmx/nested.o vmx/posted_intr.o
>>  
>> -ifdef CONFIG_HYPERV
>> -kvm-intel-y		+= vmx/vmx_onhyperv.o
>> -endif
>> +kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
>>  
>>  kvm-amd-y		+= svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o \
>> -			   svm/sev.o svm/hyperv.o
>> +			   svm/sev.o
>>  
>>  ifdef CONFIG_HYPERV
>> +kvm-y			+= kvm_onhyperv.o
>> +kvm-intel-y		+= vmx/vmx_onhyperv.o vmx/hyperv_evmcs.o
>>  kvm-amd-y		+= svm/svm_onhyperv.o
>>  endif
>>  
>> +ifdef CONFIG_KVM_HYPERV
>> +kvm-intel-y		+= vmx/hyperv.o vmx/hyperv_evmcs.o
>> +kvm-amd-y		+= svm/hyperv.o
>> +endif
>> +
>>  obj-$(CONFIG_KVM)	+= kvm.o
>>  obj-$(CONFIG_KVM_INTEL)	+= kvm-intel.o
>>  obj-$(CONFIG_KVM_AMD)	+= kvm-amd.o
>
> This also looks much better.
>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 464b23ac5f93..da8e0873f63a 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -314,11 +314,15 @@ EXPORT_SYMBOL_GPL(kvm_update_cpuid_runtime);
>>  
>>  static bool kvm_cpuid_has_hyperv(struct kvm_cpuid_entry2 *entries, int nent)
>>  {
>> +#ifdef CONFIG_KVM_HYPERV
>>  	struct kvm_cpuid_entry2 *entry;
>>  
>>  	entry = cpuid_entry2_find(entries, nent, HYPERV_CPUID_INTERFACE,
>>  				  KVM_CPUID_INDEX_NOT_SIGNIFICANT);
>>  	return entry && entry->eax == HYPERV_CPUID_SIGNATURE_EAX;
>> +#else
>> +	return false;
>> +#endif
>>  }
>>  
>>  static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>> @@ -433,11 +437,13 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
>>  		return 0;
>>  	}
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  	if (kvm_cpuid_has_hyperv(e2, nent)) {
>>  		r = kvm_hv_vcpu_init(vcpu);
>>  		if (r)
>>  			return r;
>>  	}
>> +#endif
>>  
>>  	r = kvm_check_cpuid(vcpu, e2, nent);
>>  	if (r)
>> diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
>> index 75dcbe598fbc..5c5ec7015136 100644
>> --- a/arch/x86/kvm/hyperv.h
>> +++ b/arch/x86/kvm/hyperv.h
>> @@ -24,6 +24,8 @@
>>  #include <linux/kvm_host.h>
>>  #include "x86.h"
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>> +
>>  /* "Hv#1" signature */
>>  #define HYPERV_CPUID_SIGNATURE_EAX 0x31237648
>>  
>> @@ -259,5 +261,29 @@ static inline void kvm_hv_nested_transtion_tlb_flush(struct kvm_vcpu *vcpu, bool
>>  }
>>  
>>  int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
>> -
>> -#endif
>> +#else /* CONFIG_KVM_HYPERV */
>> +static inline void kvm_hv_setup_tsc_page(struct kvm *kvm,
>> +					 struct pvclock_vcpu_time_info *hv_clock) {}
>> +static inline void kvm_hv_request_tsc_page_update(struct kvm *kvm) {}
>> +static inline void kvm_hv_init_vm(struct kvm *kvm) {}
>> +static inline void kvm_hv_destroy_vm(struct kvm *kvm) {}
>> +static inline int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu) { return 0; }
>> +static inline void kvm_hv_vcpu_uninit(struct kvm_vcpu *vcpu) {}
>> +static inline bool kvm_hv_hypercall_enabled(struct kvm_vcpu *vcpu) { return false; }
>> +static inline int kvm_hv_hypercall(struct kvm_vcpu *vcpu) { return HV_STATUS_ACCESS_DENIED; }
>> +static inline void kvm_hv_vcpu_purge_flush_tlb(struct kvm_vcpu *vcpu) {}
>> +static inline void kvm_hv_free_pa_page(struct kvm *kvm) {}
>> +static inline bool kvm_hv_synic_has_vector(struct kvm_vcpu *vcpu, int vector) { return false; }
>> +static inline bool kvm_hv_synic_auto_eoi_set(struct kvm_vcpu *vcpu, int vector) { return false; }
>> +static inline void kvm_hv_synic_send_eoi(struct kvm_vcpu *vcpu, int vector) {}
>> +static inline bool kvm_hv_invtsc_suppressed(struct kvm_vcpu *vcpu) { return false; }
>> +static inline void kvm_hv_set_cpuid(struct kvm_vcpu *vcpu, bool hyperv_enabled) {}
>> +static inline bool kvm_hv_has_stimer_pending(struct kvm_vcpu *vcpu) { return false; }
>> +static inline bool kvm_hv_is_tlb_flush_hcall(struct kvm_vcpu *vcpu) { return false; }
>> +static inline bool guest_hv_cpuid_has_l2_tlb_flush(struct kvm_vcpu *vcpu) { return false; }
>> +static inline int kvm_hv_verify_vp_assist(struct kvm_vcpu *vcpu) { return 0; }
>> +static inline u32 kvm_hv_get_vpindex(struct kvm_vcpu *vcpu) { return vcpu->vcpu_idx; }
>> +static inline void kvm_hv_nested_transtion_tlb_flush(struct kvm_vcpu *vcpu, bool tdp_enabled) {}
>> +#endif /* CONFIG_KVM_HYPERV */
>> +
>> +#endif /* __ARCH_X86_KVM_HYPERV_H__ */
>
>
>> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
>> index 16d076a1b91a..68f3f6c26046 100644
>> --- a/arch/x86/kvm/irq_comm.c
>> +++ b/arch/x86/kvm/irq_comm.c
>> @@ -144,7 +144,7 @@ int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
>>  	return kvm_irq_delivery_to_apic(kvm, NULL, &irq, NULL);
>>  }
>>  
>> -
>> +#ifdef CONFIG_KVM_HYPERV
>>  static int kvm_hv_set_sint(struct kvm_kernel_irq_routing_entry *e,
>>  		    struct kvm *kvm, int irq_source_id, int level,
>>  		    bool line_status)
>> @@ -154,6 +154,7 @@ static int kvm_hv_set_sint(struct kvm_kernel_irq_routing_entry *e,
>>  
>>  	return kvm_hv_synic_set_irq(kvm, e->hv_sint.vcpu, e->hv_sint.sint);
>>  }
>> +#endif
>>  
>>  int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
>>  			      struct kvm *kvm, int irq_source_id, int level,
>> @@ -163,9 +164,11 @@ int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
>>  	int r;
>>  
>>  	switch (e->type) {
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_IRQ_ROUTING_HV_SINT:
>>  		return kvm_hv_set_sint(e, kvm, irq_source_id, level,
>>  				       line_status);
>> +#endif
>>  
>>  	case KVM_IRQ_ROUTING_MSI:
>>  		if (kvm_msi_route_invalid(kvm, e))
>> @@ -314,11 +317,13 @@ int kvm_set_routing_entry(struct kvm *kvm,
>>  		if (kvm_msi_route_invalid(kvm, e))
>>  			return -EINVAL;
>>  		break;
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_IRQ_ROUTING_HV_SINT:
>>  		e->set = kvm_hv_set_sint;
>>  		e->hv_sint.vcpu = ue->u.hv_sint.vcpu;
>>  		e->hv_sint.sint = ue->u.hv_sint.sint;
>>  		break;
>> +#endif
>>  #ifdef CONFIG_KVM_XEN
>>  	case KVM_IRQ_ROUTING_XEN_EVTCHN:
>>  		return kvm_xen_setup_evtchn(kvm, e, ue);
>> @@ -438,5 +443,7 @@ void kvm_scan_ioapic_routes(struct kvm_vcpu *vcpu,
>>  
>>  void kvm_arch_irq_routing_update(struct kvm *kvm)
>>  {
>> +#ifdef CONFIG_KVM_HYPERV
>>  	kvm_hv_irq_routing_update(kvm);
>> +#endif
>>  }
>> diff --git a/arch/x86/kvm/svm/hyperv.h b/arch/x86/kvm/svm/hyperv.h
>> index 02f4784b5d44..14eec2d9b6be 100644
>> --- a/arch/x86/kvm/svm/hyperv.h
>> +++ b/arch/x86/kvm/svm/hyperv.h
>> @@ -11,6 +11,7 @@
>>  #include "../hyperv.h"
>>  #include "svm.h"
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu)
>>  {
>>  	struct vcpu_svm *svm = to_svm(vcpu);
>> @@ -41,5 +42,11 @@ static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu)
>>  }
>>  
>>  void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
>> +#else /* CONFIG_KVM_HYPERV */
>> +static inline void nested_svm_hv_update_vm_vp_ids(struct kvm_vcpu *vcpu) {}
>> +static inline bool nested_svm_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu) { return false; }
>> +static inline void svm_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu) {}
>> +#endif /* CONFIG_KVM_HYPERV */
>> +
>>  
>>  #endif /* __ARCH_X86_KVM_SVM_HYPERV_H__ */
>> diff --git a/arch/x86/kvm/vmx/hyperv.h b/arch/x86/kvm/vmx/hyperv.h
>> index d4ed99008518..933ef6cad5e6 100644
>> --- a/arch/x86/kvm/vmx/hyperv.h
>> +++ b/arch/x86/kvm/vmx/hyperv.h
>> @@ -20,6 +20,7 @@ enum nested_evmptrld_status {
>>  	EVMPTRLD_ERROR,
>>  };
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  u64 nested_get_evmptr(struct kvm_vcpu *vcpu);
>>  uint16_t nested_get_evmcs_version(struct kvm_vcpu *vcpu);
>>  int nested_enable_evmcs(struct kvm_vcpu *vcpu,
>> @@ -28,5 +29,12 @@ void nested_evmcs_filter_control_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *
>>  int nested_evmcs_check_controls(struct vmcs12 *vmcs12);
>>  bool nested_evmcs_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu);
>>  void vmx_hv_inject_synthetic_vmexit_post_tlb_flush(struct kvm_vcpu *vcpu);
>> +#else
>> +static inline u64 nested_get_evmptr(struct kvm_vcpu *vcpu) { return EVMPTR_INVALID; }
>> +static inline void nested_evmcs_filter_control_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata) {}
>> +static inline bool nested_evmcs_l2_tlb_flush_enabled(struct kvm_vcpu *vcpu) { return false; }
>> +static inline int nested_evmcs_check_controls(struct vmcs12 *vmcs12) { return 0; }
>> +#endif
>> +
>>  
>>  #endif /* __KVM_X86_VMX_HYPERV_H */
>> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
>> index 382c0746d069..d0d735974b2c 100644
>> --- a/arch/x86/kvm/vmx/nested.c
>> +++ b/arch/x86/kvm/vmx/nested.c
>> @@ -226,6 +226,7 @@ static void vmx_disable_shadow_vmcs(struct vcpu_vmx *vmx)
>>  
>>  static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
>>  {
>> +#ifdef CONFIG_KVM_HYPERV
>>  	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
>>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>>  
>> @@ -241,6 +242,7 @@ static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
>>  		hv_vcpu->nested.vm_id = 0;
>>  		hv_vcpu->nested.vp_id = 0;
>>  	}
>> +#endif
>>  }
>>  
>>  static void vmx_sync_vmcs_host_state(struct vcpu_vmx *vmx,
>> @@ -1570,6 +1572,7 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx)
>>  	vmcs_load(vmx->loaded_vmcs->vmcs);
>>  }
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  static void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields)
>>  {
>>  	struct vmcs12 *vmcs12 = vmx->nested.cached_vmcs12;
>> @@ -2077,6 +2080,10 @@ static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
>>  
>>  	return EVMPTRLD_SUCCEEDED;
>>  }
>> +#else /* CONFIG_KVM_HYPERV */
>> +static inline void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields) {}
>> +static inline void copy_vmcs12_to_enlightened(struct vcpu_vmx *vmx) {}
>> +#endif /* CONFIG_KVM_HYPERV */
>>  
>>  void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
>>  {
>> @@ -3155,6 +3162,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
>>  	return 0;
>>  }
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
>>  {
>>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
>> @@ -3182,6 +3190,9 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
>>  
>>  	return true;
>>  }
>> +#else
>> +static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu) { return true; }
>> +#endif
>>  
>>  static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
>>  {
>> @@ -3552,11 +3563,13 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>>  	if (!nested_vmx_check_permission(vcpu))
>>  		return 1;
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  	evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
>>  	if (evmptrld_status == EVMPTRLD_ERROR) {
>>  		kvm_queue_exception(vcpu, UD_VECTOR);
>>  		return 1;
>>  	}
>> +#endif
>>  
>>  	kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
>>  
>> @@ -7090,7 +7103,9 @@ struct kvm_x86_nested_ops vmx_nested_ops = {
>>  	.set_state = vmx_set_nested_state,
>>  	.get_nested_state_pages = vmx_get_nested_state_pages,
>>  	.write_log_dirty = nested_vmx_write_pml_buffer,
>> +#ifdef CONFIG_KVM_HYPERV
>>  	.enable_evmcs = nested_enable_evmcs,
>>  	.get_evmcs_version = nested_get_evmcs_version,
>>  	.hv_inject_synthetic_vmexit_post_tlb_flush = vmx_hv_inject_synthetic_vmexit_post_tlb_flush,
>> +#endif
>>  };
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index cc2524598368..8ef9898092cd 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -1504,6 +1504,8 @@ static unsigned num_msrs_to_save;
>>  static const u32 emulated_msrs_all[] = {
>>  	MSR_KVM_SYSTEM_TIME, MSR_KVM_WALL_CLOCK,
>>  	MSR_KVM_SYSTEM_TIME_NEW, MSR_KVM_WALL_CLOCK_NEW,
>> +
>> +#ifdef CONFIG_KVM_HYPERV
>>  	HV_X64_MSR_GUEST_OS_ID, HV_X64_MSR_HYPERCALL,
>>  	HV_X64_MSR_TIME_REF_COUNT, HV_X64_MSR_REFERENCE_TSC,
>>  	HV_X64_MSR_TSC_FREQUENCY, HV_X64_MSR_APIC_FREQUENCY,
>> @@ -1521,6 +1523,7 @@ static const u32 emulated_msrs_all[] = {
>>  	HV_X64_MSR_SYNDBG_CONTROL, HV_X64_MSR_SYNDBG_STATUS,
>>  	HV_X64_MSR_SYNDBG_SEND_BUFFER, HV_X64_MSR_SYNDBG_RECV_BUFFER,
>>  	HV_X64_MSR_SYNDBG_PENDING_BUFFER,
>> +#endif
>>  
>>  	MSR_KVM_ASYNC_PF_EN, MSR_KVM_STEAL_TIME,
>>  	MSR_KVM_PV_EOI_EN, MSR_KVM_ASYNC_PF_INT, MSR_KVM_ASYNC_PF_ACK,
>> @@ -4022,6 +4025,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  		 * the need to ignore the workaround.
>>  		 */
>>  		break;
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case HV_X64_MSR_GUEST_OS_ID ... HV_X64_MSR_SINT15:
>>  	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
>>  	case HV_X64_MSR_SYNDBG_OPTIONS:
>> @@ -4034,6 +4038,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  	case HV_X64_MSR_TSC_INVARIANT_CONTROL:
>>  		return kvm_hv_set_msr_common(vcpu, msr, data,
>>  					     msr_info->host_initiated);
>> +#endif
>>  	case MSR_IA32_BBL_CR_CTL3:
>>  		/* Drop writes to this legacy MSR -- see rdmsr
>>  		 * counterpart for further detail.
>> @@ -4378,6 +4383,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  		 */
>>  		msr_info->data = 0x20000000;
>>  		break;
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case HV_X64_MSR_GUEST_OS_ID ... HV_X64_MSR_SINT15:
>>  	case HV_X64_MSR_SYNDBG_CONTROL ... HV_X64_MSR_SYNDBG_PENDING_BUFFER:
>>  	case HV_X64_MSR_SYNDBG_OPTIONS:
>> @@ -4391,6 +4397,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>  		return kvm_hv_get_msr_common(vcpu,
>>  					     msr_info->index, &msr_info->data,
>>  					     msr_info->host_initiated);
>> +#endif
>>  	case MSR_IA32_BBL_CR_CTL3:
>>  		/* This legacy MSR exists but isn't fully documented in current
>>  		 * silicon.  It is however accessed by winxp in very narrow
>> @@ -4528,6 +4535,7 @@ static inline bool kvm_can_mwait_in_guest(void)
>>  		boot_cpu_has(X86_FEATURE_ARAT);
>>  }
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
>>  					    struct kvm_cpuid2 __user *cpuid_arg)
>>  {
>> @@ -4548,6 +4556,7 @@ static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
>>  
>>  	return 0;
>>  }
>> +#endif
>>  
>>  int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  {
>> @@ -4574,9 +4583,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  	case KVM_CAP_PIT_STATE2:
>>  	case KVM_CAP_SET_IDENTITY_MAP_ADDR:
>>  	case KVM_CAP_VCPU_EVENTS:
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_CAP_HYPERV:
>>  	case KVM_CAP_HYPERV_VAPIC:
>>  	case KVM_CAP_HYPERV_SPIN:
>> +	case KVM_CAP_HYPERV_TIME:
>>  	case KVM_CAP_HYPERV_SYNIC:
>>  	case KVM_CAP_HYPERV_SYNIC2:
>>  	case KVM_CAP_HYPERV_VP_INDEX:
>> @@ -4586,6 +4597,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  	case KVM_CAP_HYPERV_CPUID:
>>  	case KVM_CAP_HYPERV_ENFORCE_CPUID:
>>  	case KVM_CAP_SYS_HYPERV_CPUID:
>> +#endif
>>  	case KVM_CAP_PCI_SEGMENT:
>>  	case KVM_CAP_DEBUGREGS:
>>  	case KVM_CAP_X86_ROBUST_SINGLESTEP:
>> @@ -4595,7 +4607,6 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  	case KVM_CAP_GET_TSC_KHZ:
>>  	case KVM_CAP_KVMCLOCK_CTRL:
>>  	case KVM_CAP_READONLY_MEM:
>> -	case KVM_CAP_HYPERV_TIME:
>>  	case KVM_CAP_IOAPIC_POLARITY_IGNORED:
>>  	case KVM_CAP_TSC_DEADLINE_TIMER:
>>  	case KVM_CAP_DISABLE_QUIRKS:
>> @@ -4705,12 +4716,14 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>>  		r = kvm_x86_ops.nested_ops->get_state ?
>>  			kvm_x86_ops.nested_ops->get_state(NULL, NULL, 0) : 0;
>>  		break;
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
>>  		r = kvm_x86_ops.enable_l2_tlb_flush != NULL;
>>  		break;
>>  	case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
>>  		r = kvm_x86_ops.nested_ops->enable_evmcs != NULL;
>>  		break;
>> +#endif
>>  	case KVM_CAP_SMALLER_MAXPHYADDR:
>>  		r = (int) allow_smaller_maxphyaddr;
>>  		break;
>> @@ -4872,9 +4885,11 @@ long kvm_arch_dev_ioctl(struct file *filp,
>>  	case KVM_GET_MSRS:
>>  		r = msr_io(NULL, argp, do_get_msr_feature, 1);
>>  		break;
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_GET_SUPPORTED_HV_CPUID:
>>  		r = kvm_ioctl_get_supported_hv_cpuid(NULL, argp);
>>  		break;
>> +#endif
>>  	case KVM_GET_DEVICE_ATTR: {
>>  		struct kvm_device_attr attr;
>>  		r = -EFAULT;
>> @@ -5700,14 +5715,11 @@ static int kvm_vcpu_ioctl_device_attr(struct kvm_vcpu *vcpu,
>>  static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>>  				     struct kvm_enable_cap *cap)
>>  {
>> -	int r;
>> -	uint16_t vmcs_version;
>> -	void __user *user_ptr;
>> -
>>  	if (cap->flags)
>>  		return -EINVAL;
>>  
>>  	switch (cap->cap) {
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_CAP_HYPERV_SYNIC2:
>>  		if (cap->args[0])
>>  			return -EINVAL;
>> @@ -5719,16 +5731,22 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>>  		return kvm_hv_activate_synic(vcpu, cap->cap ==
>>  					     KVM_CAP_HYPERV_SYNIC2);
>>  	case KVM_CAP_HYPERV_ENLIGHTENED_VMCS:
>> -		if (!kvm_x86_ops.nested_ops->enable_evmcs)
>> -			return -ENOTTY;
>> -		r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, &vmcs_version);
>> -		if (!r) {
>> -			user_ptr = (void __user *)(uintptr_t)cap->args[0];
>> -			if (copy_to_user(user_ptr, &vmcs_version,
>> -					 sizeof(vmcs_version)))
>> -				r = -EFAULT;
>> +		{
>> +			int r;
>> +			uint16_t vmcs_version;
>> +			void __user *user_ptr;
>> +
>> +			if (!kvm_x86_ops.nested_ops->enable_evmcs)
>> +				return -ENOTTY;
>> +			r = kvm_x86_ops.nested_ops->enable_evmcs(vcpu, &vmcs_version);
>> +			if (!r) {
>> +				user_ptr = (void __user *)(uintptr_t)cap->args[0];
>> +				if (copy_to_user(user_ptr, &vmcs_version,
>> +						 sizeof(vmcs_version)))
>> +					r = -EFAULT;
>> +			}
>> +			return r;
>>  		}
>> -		return r;
>
> Minor nitpick: Unless I missed something the above is just refactoring. Can this be split
> into a separate patch?

Yea, it's even less than refactoring: basically, we just need to avoid
"unused variable" warning when !CONFIG_KVM_HYPERV so we need to declare
'vmcs_version' and 'user_ptr' locally. This can certainly be done in a
separate patch but without CONFIG_KVM_HYPERV it would look like a
no-op so I'm on the fence.

>
>
>>  	case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
>>  		if (!kvm_x86_ops.enable_l2_tlb_flush)
>>  			return -ENOTTY;
>> @@ -5737,6 +5755,7 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
>>  
>>  	case KVM_CAP_HYPERV_ENFORCE_CPUID:
>>  		return kvm_hv_set_enforce_cpuid(vcpu, cap->args[0]);
>> +#endif
>>  
>>  	case KVM_CAP_ENFORCE_PV_FEATURE_CPUID:
>>  		vcpu->arch.pv_cpuid.enforce = cap->args[0];
>> @@ -6129,9 +6148,11 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>>  		srcu_read_unlock(&vcpu->kvm->srcu, idx);
>>  		break;
>>  	}
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_GET_SUPPORTED_HV_CPUID:
>>  		r = kvm_ioctl_get_supported_hv_cpuid(vcpu, argp);
>>  		break;
>> +#endif
>>  #ifdef CONFIG_KVM_XEN
>>  	case KVM_XEN_VCPU_GET_ATTR: {
>>  		struct kvm_xen_vcpu_attr xva;
>> @@ -7189,6 +7210,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>>  		r = static_call(kvm_x86_mem_enc_unregister_region)(kvm, &region);
>>  		break;
>>  	}
>> +#ifdef CONFIG_KVM_HYPERV
>>  	case KVM_HYPERV_EVENTFD: {
>>  		struct kvm_hyperv_eventfd hvevfd;
>>  
>> @@ -7198,6 +7220,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
>>  		r = kvm_vm_ioctl_hv_eventfd(kvm, &hvevfd);
>>  		break;
>>  	}
>> +#endif
>>  	case KVM_SET_PMU_EVENT_FILTER:
>>  		r = kvm_vm_ioctl_set_pmu_event_filter(kvm, argp);
>>  		break;
>> @@ -10576,19 +10599,20 @@ static void vcpu_scan_ioapic(struct kvm_vcpu *vcpu)
>>  
>>  static void vcpu_load_eoi_exitmap(struct kvm_vcpu *vcpu)
>>  {
>> -	u64 eoi_exit_bitmap[4];
>> -
>>  	if (!kvm_apic_hw_enabled(vcpu->arch.apic))
>>  		return;
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  	if (to_hv_vcpu(vcpu)) {
>> +		u64 eoi_exit_bitmap[4];
>> +
>>  		bitmap_or((ulong *)eoi_exit_bitmap,
>>  			  vcpu->arch.ioapic_handled_vectors,
>>  			  to_hv_synic(vcpu)->vec_bitmap, 256);
>>  		static_call_cond(kvm_x86_load_eoi_exitmap)(vcpu, eoi_exit_bitmap);
>>  		return;
>>  	}
>> -
>> +#endif
>
> Same here.
>

Yep, same story: 'eoi_exit_bitmap' is only used when CONFIG_KVM_HYPERV
so we need to move it under #ifdef. I hope it's OK to keep it here as
the change is really tiny and helps us to avoid second #ifdef.

>>  	static_call_cond(kvm_x86_load_eoi_exitmap)(
>>  		vcpu, (u64 *)vcpu->arch.ioapic_handled_vectors);
>>  }
>> @@ -10679,9 +10703,11 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>  		 * the flushes are considered "remote" and not "local" because
>>  		 * the requests can be initiated from other vCPUs.
>>  		 */
>> +#ifdef CONFIG_KVM_HYPERV
>>  		if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu) &&
>>  		    kvm_hv_vcpu_flush_tlb(vcpu))
>>  			kvm_vcpu_flush_tlb_guest(vcpu);
>> +#endif
>>  
>>  		if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
>>  			vcpu->run->exit_reason = KVM_EXIT_TPR_ACCESS;
>> @@ -10734,6 +10760,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>  			vcpu_load_eoi_exitmap(vcpu);
>>  		if (kvm_check_request(KVM_REQ_APIC_PAGE_RELOAD, vcpu))
>>  			kvm_vcpu_reload_apic_access_page(vcpu);
>> +#ifdef CONFIG_KVM_HYPERV
>>  		if (kvm_check_request(KVM_REQ_HV_CRASH, vcpu)) {
>>  			vcpu->run->exit_reason = KVM_EXIT_SYSTEM_EVENT;
>>  			vcpu->run->system_event.type = KVM_SYSTEM_EVENT_CRASH;
>> @@ -10764,6 +10791,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
>>  		 */
>>  		if (kvm_check_request(KVM_REQ_HV_STIMER, vcpu))
>>  			kvm_hv_process_stimers(vcpu);
>> +#endif
>>  		if (kvm_check_request(KVM_REQ_APICV_UPDATE, vcpu))
>>  			kvm_vcpu_update_apicv(vcpu);
>>  		if (kvm_check_request(KVM_REQ_APF_READY, vcpu))
>
> Besides nitpicks,
>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
>

Thanks!

>
> Best regards,
> 	Maxim Levitsky
>
>
  

On Wed, Oct 25, 2023, Vitaly Kuznetsov wrote:
> Hyper-V emulation in KVM is a fairly big chunk and in some cases it may be
> desirable to not compile it in to reduce module sizes as well as the attack
> surface. Introduce CONFIG_KVM_HYPERV option to make it possible.
> 
> Note, there's room for further nVMX/nSVM code optimizations when
> !CONFIG_KVM_HYPERV, this will be done in follow-up patches.
> 
> Reorganize Makefile a bit so all CONFIG_HYPERV and CONFIG_KVM_HYPERV files
> are grouped together.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---

...

> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index 8ea872401cd6..b97b875ad75f 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -11,32 +11,33 @@ include $(srctree)/virt/kvm/Makefile.kvm
>  
>  kvm-y			+= x86.o emulate.o i8259.o irq.o lapic.o \
>  			   i8254.o ioapic.o irq_comm.o cpuid.o pmu.o mtrr.o \
> -			   hyperv.o debugfs.o mmu/mmu.o mmu/page_track.o \
> +			   debugfs.o mmu/mmu.o mmu/page_track.o \
>  			   mmu/spte.o
>  
> -ifdef CONFIG_HYPERV
> -kvm-y			+= kvm_onhyperv.o
> -endif
> -
>  kvm-$(CONFIG_X86_64) += mmu/tdp_iter.o mmu/tdp_mmu.o
> +kvm-$(CONFIG_KVM_HYPERV) += hyperv.o
>  kvm-$(CONFIG_KVM_XEN)	+= xen.o
>  kvm-$(CONFIG_KVM_SMM)	+= smm.o
>  
>  kvm-intel-y		+= vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
> -			   vmx/hyperv.o vmx/hyperv_evmcs.o vmx/nested.o vmx/posted_intr.o
> -kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
> +			   vmx/nested.o vmx/posted_intr.o
>  
> -ifdef CONFIG_HYPERV
> -kvm-intel-y		+= vmx/vmx_onhyperv.o
> -endif
> +kvm-intel-$(CONFIG_X86_SGX_KVM)	+= vmx/sgx.o
>  
>  kvm-amd-y		+= svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o \
> -			   svm/sev.o svm/hyperv.o
> +			   svm/sev.o
>  
>  ifdef CONFIG_HYPERV
> +kvm-y			+= kvm_onhyperv.o
> +kvm-intel-y		+= vmx/vmx_onhyperv.o vmx/hyperv_evmcs.o
>  kvm-amd-y		+= svm/svm_onhyperv.o
>  endif
>  
> +ifdef CONFIG_KVM_HYPERV
> +kvm-intel-y		+= vmx/hyperv.o vmx/hyperv_evmcs.o
> +kvm-amd-y		+= svm/hyperv.o
> +endif

My strong preference is to avoid the unnecessary ifdef and instead do:

kvm-intel-y             += vmx/vmx.o vmx/vmenter.o vmx/pmu_intel.o vmx/vmcs12.o \
                           vmx/nested.o vmx/posted_intr.o

kvm-intel-$(CONFIG_X86_SGX_KVM) += vmx/sgx.o
kvm-intel-$(CONFIG_KVM_HYPERV)  += vmx/hyperv.o vmx/hyperv_evmcs.o

kvm-amd-y               += svm/svm.o svm/vmenter.o svm/pmu.o svm/nested.o svm/avic.o \
                           svm/sev.o
kvm-amd-$(CONFIG_KVM_HYPERV)    += svm/hyperv.o


CONFIG_HYPERV needs an ifdef because it can be 'y' or 'm', but otherwise ifdefs
just tend to be noisier.

>  static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
>  {
> @@ -3552,11 +3563,13 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>  	if (!nested_vmx_check_permission(vcpu))
>  		return 1;
>  
> +#ifdef CONFIG_KVM_HYPERV
>  	evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
>  	if (evmptrld_status == EVMPTRLD_ERROR) {
>  		kvm_queue_exception(vcpu, UD_VECTOR);
>  		return 1;
>  	}
> +#endif
>  
>  	kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);

This fails to build with CONFIG_KVM_HYPERV=n && CONFIG_KVM_WERROR=y:

arch/x86/kvm/vmx/nested.c:3577:9: error: variable 'evmptrld_status' is uninitialized when used here [-Werror,-Wuninitialized]
        if (CC(evmptrld_status == EVMPTRLD_VMFAIL))
               ^~~~~~~~~~~~~~~

Sadly, simply wrapping with an #ifdef also fails because then evmptrld_status
becomes unused.  I'd really prefer to avoid having to tag it __maybe_unused, and
adding more #ifdef would also be ugly.  Any ideas?
  

On Wed, Oct 25, 2023, Vitaly Kuznetsov wrote:
> @@ -1570,6 +1572,7 @@ static void copy_vmcs12_to_shadow(struct vcpu_vmx *vmx)
>  	vmcs_load(vmx->loaded_vmcs->vmcs);
>  }
>  
> +#ifdef CONFIG_KVM_HYPERV
>  static void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields)
>  {
>  	struct vmcs12 *vmcs12 = vmx->nested.cached_vmcs12;
> @@ -2077,6 +2080,10 @@ static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
>  
>  	return EVMPTRLD_SUCCEEDED;
>  }
> +#else /* CONFIG_KVM_HYPERV */
> +static inline void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields) {}
> +static inline void copy_vmcs12_to_enlightened(struct vcpu_vmx *vmx) {}

I'm not sure I love the stubs in .c code.  What if we instead throw the #ifdef
inside the helper, and then add a KVM_BUG_ON() in the CONFIG_KVM_HYPERV=n path?

> +#endif /* CONFIG_KVM_HYPERV */
>  
>  void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
>  {
> @@ -3155,6 +3162,7 @@ static int nested_vmx_check_vmentry_hw(struct kvm_vcpu *vcpu)
>  	return 0;
>  }
>  
> +#ifdef CONFIG_KVM_HYPERV
>  static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
>  {
>  	struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -3182,6 +3190,9 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
>  
>  	return true;
>  }
> +#else
> +static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu) { return true; }
> +#endif

And this one seems like it could be cleaner to just #ifdef the callers.
  

Sean Christopherson <seanjc@google.com> writes:

...

>
>>  static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
>>  {
>> @@ -3552,11 +3563,13 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>>  	if (!nested_vmx_check_permission(vcpu))
>>  		return 1;
>>  
>> +#ifdef CONFIG_KVM_HYPERV
>>  	evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
>>  	if (evmptrld_status == EVMPTRLD_ERROR) {
>>  		kvm_queue_exception(vcpu, UD_VECTOR);
>>  		return 1;
>>  	}
>> +#endif
>>  
>>  	kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
>
> This fails to build with CONFIG_KVM_HYPERV=n && CONFIG_KVM_WERROR=y:
>
> arch/x86/kvm/vmx/nested.c:3577:9: error: variable 'evmptrld_status' is uninitialized when used here [-Werror,-Wuninitialized]
>         if (CC(evmptrld_status == EVMPTRLD_VMFAIL))
>                ^~~~~~~~~~~~~~~
>
> Sadly, simply wrapping with an #ifdef also fails because then evmptrld_status
> becomes unused.  I'd really prefer to avoid having to tag it __maybe_unused, and
> adding more #ifdef would also be ugly.  Any ideas?

A couple,

- we can try putting all eVMPTR logic under 'if (1)' just to create a
  block where we can define evmptrld_status. Not sure this is nicer than
  another #ifdef wrapping evmptrld_status and I'm not sure what to do
  with kvm_pmu_trigger_event() -- can it just go above
  nested_vmx_handle_enlightened_vmptrld()?

- we can add a helper, e.g. 'evmptr_is_vmfail()' and make it just return
  'false' when !CONFIG_KVM_HYPERV.

- rewrite this as a switch to avoid the need for having the local
  variable, (untested)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index c5ec0ef51ff7..b26ce7d596e9 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3553,22 +3553,23 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
        enum nvmx_vmentry_status status;
        struct vcpu_vmx *vmx = to_vmx(vcpu);
        u32 interrupt_shadow = vmx_get_interrupt_shadow(vcpu);
-       enum nested_evmptrld_status evmptrld_status;
 
        if (!nested_vmx_check_permission(vcpu))
                return 1;
 
-       evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
-       if (evmptrld_status == EVMPTRLD_ERROR) {
+       switch (nested_vmx_handle_enlightened_vmptrld(vcpu, launch)) {
+       case EVMPTRLD_ERROR:
                kvm_queue_exception(vcpu, UD_VECTOR);
                return 1;
+       case EVMPTRLD_VMFAIL:
+               trace_kvm_nested_vmenter_failed("evmptrld_status", 0);
+               return nested_vmx_failInvalid(vcpu);
+       default:
+               break;
        }
 
        kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
 
-       if (CC(evmptrld_status == EVMPTRLD_VMFAIL))
-               return nested_vmx_failInvalid(vcpu);
-
        if (CC(!evmptr_is_valid(vmx->nested.hv_evmcs_vmptr) &&
               vmx->nested.current_vmptr == INVALID_GPA))
                return nested_vmx_failInvalid(vcpu);

Unfortunately, I had to open code CC() ;-(

Or maybe just another "#ifdef" is not so ugly after all? :-)
  

On Thu, Nov 30, 2023, Vitaly Kuznetsov wrote:
> Sean Christopherson <seanjc@google.com> writes:
> 
> ...
> 
> >
> >>  static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
> >>  {
> >> @@ -3552,11 +3563,13 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
> >>  	if (!nested_vmx_check_permission(vcpu))
> >>  		return 1;
> >>  
> >> +#ifdef CONFIG_KVM_HYPERV
> >>  	evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
> >>  	if (evmptrld_status == EVMPTRLD_ERROR) {
> >>  		kvm_queue_exception(vcpu, UD_VECTOR);
> >>  		return 1;
> >>  	}
> >> +#endif
> >>  
> >>  	kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
> >
> > This fails to build with CONFIG_KVM_HYPERV=n && CONFIG_KVM_WERROR=y:
> >
> > arch/x86/kvm/vmx/nested.c:3577:9: error: variable 'evmptrld_status' is uninitialized when used here [-Werror,-Wuninitialized]
> >         if (CC(evmptrld_status == EVMPTRLD_VMFAIL))
> >                ^~~~~~~~~~~~~~~
> >
> > Sadly, simply wrapping with an #ifdef also fails because then evmptrld_status
> > becomes unused.  I'd really prefer to avoid having to tag it __maybe_unused, and
> > adding more #ifdef would also be ugly.  Any ideas?
> 
> A couple,
> 
> - we can try putting all eVMPTR logic under 'if (1)' just to create a
>   block where we can define evmptrld_status. Not sure this is nicer than
>   another #ifdef wrapping evmptrld_status and I'm not sure what to do
>   with kvm_pmu_trigger_event() -- can it just go above
>   nested_vmx_handle_enlightened_vmptrld()?
> 
> - we can add a helper, e.g. 'evmptr_is_vmfail()' and make it just return
>   'false' when !CONFIG_KVM_HYPERV.
> 
> - rewrite this as a switch to avoid the need for having the local
>   variable, (untested)
> 
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index c5ec0ef51ff7..b26ce7d596e9 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -3553,22 +3553,23 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
>         enum nvmx_vmentry_status status;
>         struct vcpu_vmx *vmx = to_vmx(vcpu);
>         u32 interrupt_shadow = vmx_get_interrupt_shadow(vcpu);
> -       enum nested_evmptrld_status evmptrld_status;
>  
>         if (!nested_vmx_check_permission(vcpu))
>                 return 1;
>  
> -       evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
> -       if (evmptrld_status == EVMPTRLD_ERROR) {
> +       switch (nested_vmx_handle_enlightened_vmptrld(vcpu, launch)) {
> +       case EVMPTRLD_ERROR:
>                 kvm_queue_exception(vcpu, UD_VECTOR);
>                 return 1;
> +       case EVMPTRLD_VMFAIL:
> +               trace_kvm_nested_vmenter_failed("evmptrld_status", 0);
> +               return nested_vmx_failInvalid(vcpu);
> +       default:
> +               break;
>         }
>  
>         kvm_pmu_trigger_event(vcpu, PERF_COUNT_HW_BRANCH_INSTRUCTIONS);
>  
> -       if (CC(evmptrld_status == EVMPTRLD_VMFAIL))
> -               return nested_vmx_failInvalid(vcpu);
> -
>         if (CC(!evmptr_is_valid(vmx->nested.hv_evmcs_vmptr) &&
>                vmx->nested.current_vmptr == INVALID_GPA))
>                 return nested_vmx_failInvalid(vcpu);
> 
> Unfortunately, I had to open code CC() ;-(
> 
> Or maybe just another "#ifdef" is not so ugly after all? :-)

Ah, just have nested_vmx_handle_enlightened_vmptrld() return EVMPTRLD_DISABLED
for its "stub", e.g. with some otehr tangentially de-stubbing:

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 4777d867419c..5a27a2ebbb32 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2000,6 +2000,7 @@ static void copy_vmcs12_to_enlightened(struct vcpu_vmx *vmx)
 static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
        struct kvm_vcpu *vcpu, bool from_launch)
 {
+#ifdef CONFIG_KVM_HYPERV
        struct vcpu_vmx *vmx = to_vmx(vcpu);
        bool evmcs_gpa_changed = false;
        u64 evmcs_gpa;
@@ -2081,11 +2082,10 @@ static enum nested_evmptrld_status nested_vmx_handle_enlightened_vmptrld(
        }
 
        return EVMPTRLD_SUCCEEDED;
+#else
+       return EVMPTRLD_DISABLED;
+#endif
 }
-#else /* CONFIG_KVM_HYPERV */
-static inline void copy_enlightened_to_vmcs12(struct vcpu_vmx *vmx, u32 hv_clean_fields) {}
-static inline void copy_vmcs12_to_enlightened(struct vcpu_vmx *vmx) {}
-#endif /* CONFIG_KVM_HYPERV */
 
 void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
 {
@@ -3191,8 +3191,6 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
 
        return true;
 }
-#else
-static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu) { return true; }
 #endif
 
 static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
@@ -3285,6 +3283,7 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 
 static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
 {
+#ifdef CONFIG_KVM_HYPERV
        /*
         * Note: nested_get_evmcs_page() also updates 'vp_assist_page' copy
         * in 'struct kvm_vcpu_hv' in case eVMCS is in use, this is mandatory
@@ -3301,7 +3300,7 @@ static bool vmx_get_nested_state_pages(struct kvm_vcpu *vcpu)
 
                return false;
        }
-
+#endif
        if (is_guest_mode(vcpu) && !nested_get_vmcs12_pages(vcpu))
                return false;
 
@@ -3564,7 +3563,6 @@ static int nested_vmx_run(struct kvm_vcpu *vcpu, bool launch)
        if (!nested_vmx_check_permission(vcpu))
                return 1;
 
-#ifdef CONFIG_KVM_HYPERV
        evmptrld_status = nested_vmx_handle_enlightened_vmptrld(vcpu, launch);
        if (evmptrld_status == EVMPTRLD_ERROR) {
                kvm_queue_exception(vcpu, UD_VECTOR);
@@ -4743,6 +4741,7 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
        WARN_ON_ONCE(vmx->nested.nested_run_pending);
 
        if (kvm_check_request(KVM_REQ_GET_NESTED_STATE_PAGES, vcpu)) {
+#ifdef CONFIG_KVM_HYPERV
                /*
                 * KVM_REQ_GET_NESTED_STATE_PAGES is also used to map
                 * Enlightened VMCS after migration and we still need to
@@ -4750,6 +4749,7 @@ void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 vm_exit_reason,
                 * the first L2 run.
                 */
                (void)nested_get_evmcs_page(vcpu);
+#endif
        }
 
        /* Service pending TLB flush requests for L2 before switching to L1. */