diff mbox series

[v3,09/21] KVM:x86: Load guest FPU state when accessing xsaves-managed MSRs

Message ID 20230511040857.6094-10-weijiang.yang@intel.com
State New
Headers
Series Enable CET Virtualization |

Commit Message

Yang, Weijiang May 11, 2023, 4:08 a.m. UTC 
  From: Sean Christopherson <sean.j.christopherson@intel.com>

Load the guest's FPU state if userspace is accessing MSRs whose values are
managed by XSAVES. Two MSR access helpers, i.e., kvm_{get,set}_xsave_msr(),
are introduced by a later patch to facilitate access to this kind of MSRs.

If new feature MSRs supported in XSS are passed through to the guest they
are saved and restored by {XSAVES|XRSTORS} to/from guest's FPU state at
vm-entry/exit.

Because the modified code is also used for the KVM_GET_MSRS device ioctl(),
explicitly check @vcpu is non-null before attempting to load guest state.
The XSS supporting MSRs cannot be retrieved via the device ioctl() without
loading guest FPU state (which doesn't exist).

Note that guest_cpuid_has() is not queried as host userspace is allowed
to access MSRs that have not been exposed to the guest, e.g. it might do
KVM_SET_MSRS prior to KVM_SET_CPUID2.

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Co-developed-by: Yang Weijiang <weijiang.yang@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
---
 arch/x86/kvm/x86.c | 29 ++++++++++++++++++++++++++++-
 1 file changed, 28 insertions(+), 1 deletion(-)

Comments

Sean Christopherson June 15, 2023, 11:50 p.m. UTC | #1 
On Thu, May 11, 2023, Yang Weijiang wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
> 
> Load the guest's FPU state if userspace is accessing MSRs whose values are
> managed by XSAVES. Two MSR access helpers, i.e., kvm_{get,set}_xsave_msr(),
> are introduced by a later patch to facilitate access to this kind of MSRs.
> 
> If new feature MSRs supported in XSS are passed through to the guest they
> are saved and restored by {XSAVES|XRSTORS} to/from guest's FPU state at
> vm-entry/exit.
> 
> Because the modified code is also used for the KVM_GET_MSRS device ioctl(),
> explicitly check @vcpu is non-null before attempting to load guest state.
> The XSS supporting MSRs cannot be retrieved via the device ioctl() without
> loading guest FPU state (which doesn't exist).
> 
> Note that guest_cpuid_has() is not queried as host userspace is allowed
> to access MSRs that have not been exposed to the guest, e.g. it might do
> KVM_SET_MSRS prior to KVM_SET_CPUID2.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Co-developed-by: Yang Weijiang <weijiang.yang@intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>  arch/x86/kvm/x86.c | 29 ++++++++++++++++++++++++++++-
>  1 file changed, 28 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d2975ca96ac5..7788646bbf1f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -130,6 +130,9 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
>  static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
>  
>  static DEFINE_MUTEX(vendor_module_lock);
> +static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
> +static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
> +
>  struct kvm_x86_ops kvm_x86_ops __read_mostly;
>  
>  #define KVM_X86_OP(func)					     \
> @@ -4336,6 +4339,21 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  }
>  EXPORT_SYMBOL_GPL(kvm_get_msr_common);
>  
> +static const u32 xsave_msrs[] = {

Can you change this to "xstate_msrs"?


> +	MSR_IA32_U_CET, MSR_IA32_PL3_SSP,
> +};
> +
> +static bool is_xsaves_msr(u32 index)

And then is_xstate_msr().  The intent to is check if an MSR is managed as part of
the xstate, not if the MSR is somehow related to XSAVE itself.
Yang, Weijiang June 16, 2023, 2:02 a.m. UTC | #2 
On 6/16/2023 7:50 AM, Sean Christopherson wrote:
> On Thu, May 11, 2023, Yang Weijiang wrote:
>> From: Sean Christopherson <sean.j.christopherson@intel.com>
>>
>> Load the guest's FPU state if userspace is accessing MSRs whose values are
>> managed by XSAVES. Two MSR access helpers, i.e., kvm_{get,set}_xsave_msr(),
>> are introduced by a later patch to facilitate access to this kind of MSRs.
>>
>>
>> [...]
>>   
>>   #define KVM_X86_OP(func)					     \
>> @@ -4336,6 +4339,21 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>>   }
>>   EXPORT_SYMBOL_GPL(kvm_get_msr_common);
>>   
>> +static const u32 xsave_msrs[] = {
> Can you change this to "xstate_msrs"?
OK, will change it in next version.
>
>
>> +	MSR_IA32_U_CET, MSR_IA32_PL3_SSP,
>> +};
>> +
>> +static bool is_xsaves_msr(u32 index)
> And then is_xstate_msr().  The intent to is check if an MSR is managed as part of
> the xstate, not if the MSR is somehow related to XSAVE itself.
Make sense, will change it. Thanks!
diff mbox series

Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d2975ca96ac5..7788646bbf1f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -130,6 +130,9 @@  static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
 static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
 
 static DEFINE_MUTEX(vendor_module_lock);
+static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu);
+static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu);
+
 struct kvm_x86_ops kvm_x86_ops __read_mostly;
 
 #define KVM_X86_OP(func)					     \
@@ -4336,6 +4339,21 @@  int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 }
 EXPORT_SYMBOL_GPL(kvm_get_msr_common);
 
+static const u32 xsave_msrs[] = {
+	MSR_IA32_U_CET, MSR_IA32_PL3_SSP,
+};
+
+static bool is_xsaves_msr(u32 index)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(xsave_msrs); i++) {
+		if (index == xsave_msrs[i])
+			return true;
+	}
+	return false;
+}
+
 /*
  * Read or write a bunch of msrs. All parameters are kernel addresses.
  *
@@ -4346,11 +4364,20 @@  static int __msr_io(struct kvm_vcpu *vcpu, struct kvm_msrs *msrs,
 		    int (*do_msr)(struct kvm_vcpu *vcpu,
 				  unsigned index, u64 *data))
 {
+	bool fpu_loaded = false;
 	int i;
 
-	for (i = 0; i < msrs->nmsrs; ++i)
+	for (i = 0; i < msrs->nmsrs; ++i) {
+		if (vcpu && !fpu_loaded && kvm_caps.supported_xss &&
+		    is_xsaves_msr(entries[i].index)) {
+			kvm_load_guest_fpu(vcpu);
+			fpu_loaded = true;
+		}
 		if (do_msr(vcpu, entries[i].index, &entries[i].data))
 			break;
+	}
+	if (fpu_loaded)
+		kvm_put_guest_fpu(vcpu);
 
 	return i;
 }