Re: [PATCH v2 3/6] KVM: x86/mmu: only zap EPT when guest MTRR changes

Chao Gao
2023-05-10T05:40:52Z

On Tue, May 09, 2023 at 09:51:43PM +0800, Yan Zhao wrote:
>Call new helper kvm_zap_gfn_for_memtype() to skip zap mmu if EPT is not
>enabled.
>
>When guest MTRR changes and it's desired to zap TDP entries to remove
>stale mappings, only do it when EPT is enabled, because only memory type
>of EPT leaf is affected by guest MTRR with noncoherent DMA present.
>
>Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
>---
> arch/x86/kvm/mtrr.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
>diff --git a/arch/x86/kvm/mtrr.c b/arch/x86/kvm/mtrr.c
>index 9fac1ec03463..62ebb9978156 100644
>--- a/arch/x86/kvm/mtrr.c
>+++ b/arch/x86/kvm/mtrr.c
>@@ -330,7 +330,7 @@ static void update_mtrr(struct kvm_vcpu *vcpu, u32 msr)
> var_mtrr_range(&mtrr_state->var_ranges[index], &start, &end);
> }
>
>- kvm_zap_gfn_range(vcpu->kvm, gpa_to_gfn(start), gpa_to_gfn(end));
>+ kvm_zap_gfn_for_memtype(vcpu->kvm, gpa_to_gfn(start), gpa_to_gfn(end));

I am wondering if the check of shadow_memtype_mask (now inside the
kvm_zap_gfn_for_memtype()) should be moved to the beginning of update_mtrr().
Because if EPT isn't enabled, computing @start/@end is useless and can be
skipped.

> }
>
> static bool var_mtrr_range_is_valid(struct kvm_mtrr_range *range)
>--
>2.17.1
>