[v3] KVM: x86/mmu: refine memtype related mmu zap

[PATCH v3 03/11] KVM: x86/mmu: Use KVM honors guest MTRRs helper when CR0.CD toggles

Posted by Yan Zhao 2 years, 7 months ago

Call helper to check if guest MTRRs are honored by KVM MMU before zapping,
as values of guest CR0.CD will only affect memory types of KVM TDP when
guest MTRRs are honored.

Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
---
 arch/x86/kvm/x86.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9e7186864542..6693daeb5686 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -942,7 +942,7 @@ void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned lon
 		kvm_mmu_reset_context(vcpu);
 
 	if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
-	    kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
+	    kvm_mmu_honors_guest_mtrrs(vcpu->kvm) &&
 	    !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
 		kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
 }
-- 
2.17.1

Re: [PATCH v3 03/11] KVM: x86/mmu: Use KVM honors guest MTRRs helper when CR0.CD toggles

Posted by Sean Christopherson 2 years, 7 months ago

On Fri, Jun 16, 2023, Yan Zhao wrote:
> Call helper to check if guest MTRRs are honored by KVM MMU before zapping,

Nit, state the effect, not what the code literally does.  The important part is
that the end result is that KVM will zap if and only if guest MTRRs are being
honored, e.g.

  Zap SPTEs when CR0.CD is toggled if and only if KVM's MMU is honoring
  guest MTRRs, which is the only time that KVM incorporates the guest's
  CR0.CD into the final memtype.

> as values of guest CR0.CD will only affect memory types of KVM TDP when
> guest MTRRs are honored.
> 
> Suggested-by: Chao Gao <chao.gao@intel.com>
> Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
> ---
>  arch/x86/kvm/x86.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 9e7186864542..6693daeb5686 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -942,7 +942,7 @@ void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0, unsigned lon
>  		kvm_mmu_reset_context(vcpu);
>  
>  	if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
> -	    kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
> +	    kvm_mmu_honors_guest_mtrrs(vcpu->kvm) &&
>  	    !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
>  		kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
>  }
> -- 
> 2.17.1
>

Re: [PATCH v3 03/11] KVM: x86/mmu: Use KVM honors guest MTRRs helper when CR0.CD toggles

Posted by Yan Zhao 2 years, 7 months ago

On Wed, Jun 28, 2023 at 02:59:00PM -0700, Sean Christopherson wrote:
> On Fri, Jun 16, 2023, Yan Zhao wrote:
> > Call helper to check if guest MTRRs are honored by KVM MMU before zapping,
> 
> Nit, state the effect, not what the code literally does.  The important part is
> that the end result is that KVM will zap if and only if guest MTRRs are being
> honored, e.g.
> 
>   Zap SPTEs when CR0.CD is toggled if and only if KVM's MMU is honoring
>   guest MTRRs, which is the only time that KVM incorporates the guest's
>   CR0.CD into the final memtype.
> 
Thanks! Will update it.