[PATCH] KVM: nSVM: Additions to optimizing L12 to L2 vmcb.save copies

[PATCH] KVM: nSVM: Additions to optimizing L12 to L2 vmcb.save copies

[Cathy Avery]

Extend using the vmcb12 control clean field to determine which
vmcb12.save registers were marked dirty in order to minimize
register copies by including the CR bit.

This patch also fixes the init of last_vmcb12_gpa by using an invalid
physical address instead of 0.

Tested:
kvm-unit-tests
kvm selftests
Fedora L1 L2

Signed-off-by: Cathy Avery <cavery@redhat.com>
---
 arch/x86/kvm/svm/nested.c | 9 ++++++---
 arch/x86/kvm/svm/svm.c    | 2 +-
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 8523f60adb92..6f9a40e002bc 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -449,9 +449,12 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
 	}
 
 	kvm_set_rflags(&svm->vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);
-	svm_set_efer(&svm->vcpu, vmcb12->save.efer);
-	svm_set_cr0(&svm->vcpu, vmcb12->save.cr0);
-	svm_set_cr4(&svm->vcpu, vmcb12->save.cr4);
+
+	if (unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_CR))) {
+		svm_set_efer(&svm->vcpu, vmcb12->save.efer);
+		svm_set_cr0(&svm->vcpu, vmcb12->save.cr0);
+		svm_set_cr4(&svm->vcpu, vmcb12->save.cr4);
+	}
 
 	svm->vcpu.arch.cr2 = vmcb12->save.cr2;
 
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 271196400495..41f5cd1009ca 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1234,7 +1234,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
 	svm->asid = 0;
 
 	svm->nested.vmcb12_gpa = 0;
-	svm->nested.last_vmcb12_gpa = 0;
+	svm->nested.last_vmcb12_gpa = -1;
 	vcpu->arch.hflags = 0;
 
 	if (!kvm_pause_in_guest(vcpu->kvm)) {
-- 
2.26.2

Re: [PATCH] KVM: nSVM: Additions to optimizing L12 to L2 vmcb.save copies

[Sean Christopherson]

On Wed, Mar 17, 2021, Cathy Avery wrote:
> Extend using the vmcb12 control clean field to determine which
> vmcb12.save registers were marked dirty in order to minimize
> register copies by including the CR bit.
> 
> This patch also fixes the init of last_vmcb12_gpa by using an invalid
> physical address instead of 0.
> 
> Tested:
> kvm-unit-tests
> kvm selftests
> Fedora L1 L2
> 
> Signed-off-by: Cathy Avery <cavery@redhat.com>
> ---
>  arch/x86/kvm/svm/nested.c | 9 ++++++---
>  arch/x86/kvm/svm/svm.c    | 2 +-
>  2 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
> index 8523f60adb92..6f9a40e002bc 100644
> --- a/arch/x86/kvm/svm/nested.c
> +++ b/arch/x86/kvm/svm/nested.c
> @@ -449,9 +449,12 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12
>  	}
>  
>  	kvm_set_rflags(&svm->vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);
> -	svm_set_efer(&svm->vcpu, vmcb12->save.efer);
> -	svm_set_cr0(&svm->vcpu, vmcb12->save.cr0);
> -	svm_set_cr4(&svm->vcpu, vmcb12->save.cr4);
> +
> +	if (unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_CR))) {
> +		svm_set_efer(&svm->vcpu, vmcb12->save.efer);
> +		svm_set_cr0(&svm->vcpu, vmcb12->save.cr0);
> +		svm_set_cr4(&svm->vcpu, vmcb12->save.cr4);

This doesn't seem correct.  Regardless of when vmcb12 was last touched, KVM
still needs to set L2's state in vcpu->arch and set the correct MMU context.

> +	}
>  
>  	svm->vcpu.arch.cr2 = vmcb12->save.cr2;
>  
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 271196400495..41f5cd1009ca 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1234,7 +1234,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
>  	svm->asid = 0;
>  
>  	svm->nested.vmcb12_gpa = 0;
> -	svm->nested.last_vmcb12_gpa = 0;
> +	svm->nested.last_vmcb12_gpa = -1;

INVALID_PAGE would be even better.

>  	vcpu->arch.hflags = 0;
>  
>  	if (!kvm_pause_in_guest(vcpu->kvm)) {
> -- 
> 2.26.2
>