diff mbox series

[2/2] KVM: x86: Open code all direct reads to guest DR6 and DR7

Message ID 20240209220752.388160-3-seanjc@google.com
State New
Headers
Series KVM: x86: Cleanup kvm_get_dr() usage |

Commit Message

Sean Christopherson Feb. 9, 2024, 10:07 p.m. UTC 
  Bite the bullet, and open code all direct reads of DR6 and DR7.  KVM
currently has a mix of open coded accesses and calls to kvm_get_dr(),
which is confusing and ugly because there's no rhyme or reason as to why
any particular chunk of code uses kvm_get_dr().

The obvious alternative is to force all accesses through kvm_get_dr(),
but it's not at all clear that doing so would be a net positive, e.g. even
if KVM ends up wanting/needing to force all reads through a common helper,
e.g. to play caching games, the cost of reverting this change is likely
lower than the ongoing cost of maintaining weird, arbitrary code.

No functional change intended.

Cc: Mathias Krause <minipli@grsecurity.net>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/smm.c        | 8 ++++----
 arch/x86/kvm/vmx/nested.c | 2 +-
 arch/x86/kvm/x86.c        | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

Comments

Mathias Krause Feb. 9, 2024, 10:30 p.m. UTC | #1 
On 09.02.24 23:07, Sean Christopherson wrote:
> Bite the bullet, and open code all direct reads of DR6 and DR7.  KVM
> currently has a mix of open coded accesses and calls to kvm_get_dr(),
> which is confusing and ugly because there's no rhyme or reason as to why
> any particular chunk of code uses kvm_get_dr().
> 
> The obvious alternative is to force all accesses through kvm_get_dr(),
> but it's not at all clear that doing so would be a net positive, e.g. even
> if KVM ends up wanting/needing to force all reads through a common helper,
> e.g. to play caching games, the cost of reverting this change is likely
> lower than the ongoing cost of maintaining weird, arbitrary code.
> 
> No functional change intended.
> 
> Cc: Mathias Krause <minipli@grsecurity.net>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  arch/x86/kvm/smm.c        | 8 ++++----
>  arch/x86/kvm/vmx/nested.c | 2 +-
>  arch/x86/kvm/x86.c        | 2 +-
>  3 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
> index 19a7a0a31953..d06d43d8d2aa 100644
> --- a/arch/x86/kvm/smm.c
> +++ b/arch/x86/kvm/smm.c
> @@ -194,8 +194,8 @@ static void enter_smm_save_state_32(struct kvm_vcpu *vcpu,
>  	for (i = 0; i < 8; i++)
>  		smram->gprs[i] = kvm_register_read_raw(vcpu, i);
>  
> -	smram->dr6     = (u32)kvm_get_dr(vcpu, 6);
> -	smram->dr7     = (u32)kvm_get_dr(vcpu, 7);
> +	smram->dr6     = (u32)vcpu->arch.dr6;
> +	smram->dr7     = (u32)vcpu->arch.dr7;
>  
>  	enter_smm_save_seg_32(vcpu, &smram->tr, &smram->tr_sel, VCPU_SREG_TR);
>  	enter_smm_save_seg_32(vcpu, &smram->ldtr, &smram->ldtr_sel, VCPU_SREG_LDTR);
> @@ -236,8 +236,8 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
>  	smram->rip    = kvm_rip_read(vcpu);
>  	smram->rflags = kvm_get_rflags(vcpu);
>  
> -	smram->dr6 = kvm_get_dr(vcpu, 6);
> -	smram->dr7 = kvm_get_dr(vcpu, 7);
> +	smram->dr6 = vcpu->arch.dr6;
> +	smram->dr7 = vcpu->arch.dr7;
>  
>  	smram->cr0 = kvm_read_cr0(vcpu);
>  	smram->cr3 = kvm_read_cr3(vcpu);
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 28d1088a1770..d05ddf751491 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -4433,7 +4433,7 @@ static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
>  		(vm_entry_controls_get(to_vmx(vcpu)) & VM_ENTRY_IA32E_MODE);
>  
>  	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_DEBUG_CONTROLS)
> -		vmcs12->guest_dr7 = kvm_get_dr(vcpu, 7);
> +		vmcs12->guest_dr7 = vcpu->arch.dr7;
>  
>  	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_IA32_EFER)
>  		vmcs12->guest_ia32_efer = vcpu->arch.efer;
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bfffc13f91e6..5a08d895bde6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5510,7 +5510,7 @@ static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
>  	for (i = 0; i < ARRAY_SIZE(vcpu->arch.db); i++)
>  		dbgregs->db[i] = vcpu->arch.db[i];
>  
> -	dbgregs->dr6 = kvm_get_dr(vcpu, 6);
> +	dbgregs->dr6 = vcpu->arch.dr6;
>  	dbgregs->dr7 = vcpu->arch.dr7;
>  }
>  

Reviewed-by: Mathias Krause <minipli@grsecurity.net>

Nice cleanup. Thanks a lot, Sean!
diff mbox series

Patch

diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index 19a7a0a31953..d06d43d8d2aa 100644
--- a/arch/x86/kvm/smm.c
+++ b/arch/x86/kvm/smm.c
@@ -194,8 +194,8 @@  static void enter_smm_save_state_32(struct kvm_vcpu *vcpu,
 	for (i = 0; i < 8; i++)
 		smram->gprs[i] = kvm_register_read_raw(vcpu, i);
 
-	smram->dr6     = (u32)kvm_get_dr(vcpu, 6);
-	smram->dr7     = (u32)kvm_get_dr(vcpu, 7);
+	smram->dr6     = (u32)vcpu->arch.dr6;
+	smram->dr7     = (u32)vcpu->arch.dr7;
 
 	enter_smm_save_seg_32(vcpu, &smram->tr, &smram->tr_sel, VCPU_SREG_TR);
 	enter_smm_save_seg_32(vcpu, &smram->ldtr, &smram->ldtr_sel, VCPU_SREG_LDTR);
@@ -236,8 +236,8 @@  static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
 	smram->rip    = kvm_rip_read(vcpu);
 	smram->rflags = kvm_get_rflags(vcpu);
 
-	smram->dr6 = kvm_get_dr(vcpu, 6);
-	smram->dr7 = kvm_get_dr(vcpu, 7);
+	smram->dr6 = vcpu->arch.dr6;
+	smram->dr7 = vcpu->arch.dr7;
 
 	smram->cr0 = kvm_read_cr0(vcpu);
 	smram->cr3 = kvm_read_cr3(vcpu);
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 28d1088a1770..d05ddf751491 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4433,7 +4433,7 @@  static void sync_vmcs02_to_vmcs12(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12)
 		(vm_entry_controls_get(to_vmx(vcpu)) & VM_ENTRY_IA32E_MODE);
 
 	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_DEBUG_CONTROLS)
-		vmcs12->guest_dr7 = kvm_get_dr(vcpu, 7);
+		vmcs12->guest_dr7 = vcpu->arch.dr7;
 
 	if (vmcs12->vm_exit_controls & VM_EXIT_SAVE_IA32_EFER)
 		vmcs12->guest_ia32_efer = vcpu->arch.efer;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bfffc13f91e6..5a08d895bde6 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5510,7 +5510,7 @@  static void kvm_vcpu_ioctl_x86_get_debugregs(struct kvm_vcpu *vcpu,
 	for (i = 0; i < ARRAY_SIZE(vcpu->arch.db); i++)
 		dbgregs->db[i] = vcpu->arch.db[i];
 
-	dbgregs->dr6 = kvm_get_dr(vcpu, 6);
+	dbgregs->dr6 = vcpu->arch.dr6;
 	dbgregs->dr7 = vcpu->arch.dr7;
 }