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

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