Re: [PATCH v2 1/6] KVM: x86/mmu: add a new mmu zap helper to indicate memtype changes

[Chao Gao]

On Tue, May 09, 2023 at 09:50:06PM +0800, Yan Zhao wrote:
>Add a helper to indicate that the kvm_zap_gfn_range() request is to update
>memory type.
>
>Then the zap can be avoided in cases:
>1. TDP is not enabled.
>2. EPT is not enabled.
>
>This is because only memory type of EPT leaf entries are subjected to
>change when noncoherent DMA/guest CR0.CD/guest MTRR settings change.
>
>Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
>---
> arch/x86/kvm/mmu.h     |  1 +
> arch/x86/kvm/mmu/mmu.c | 16 ++++++++++++++++
> 2 files changed, 17 insertions(+)
>
>diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
>index 92d5a1924fc1..a04577afbc71 100644
>--- a/arch/x86/kvm/mmu.h
>+++ b/arch/x86/kvm/mmu.h
>@@ -236,6 +236,7 @@ static inline u8 permission_fault(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
> }
> 
> void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);
>+void kvm_zap_gfn_for_memtype(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end);
> 
> int kvm_arch_write_log_dirty(struct kvm_vcpu *vcpu);
> 
>diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>index c8961f45e3b1..2706754794d1 100644
>--- a/arch/x86/kvm/mmu/mmu.c
>+++ b/arch/x86/kvm/mmu/mmu.c
>@@ -6272,6 +6272,22 @@ static bool kvm_rmap_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_e
> 	return flush;
> }
> 
>+/*
>+ * Invalidate (zap) TDP SPTEs that cover GFNs from gfn_start and up to gfn_end
>+ * (not including it) for reason of memory type being updated.
>+ */
>+void kvm_zap_gfn_for_memtype(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
>+{
>+	/* Currently only memory type of EPT leaf entries are affected by
>+	 * guest CR0.CD and guest MTRR.
>+	 * So skip invalidation (zap) in other cases
>+	 */
>+	if (!shadow_memtype_mask)

Do you need to check kvm_arch_has_noncoherent_dma()? if yes, maybe just extract
the first if() statement and its associated comment from kvm_tdp_page_fault()?

>+		return;
>+
>+	kvm_zap_gfn_range(kvm, gpa_to_gfn(0), gpa_to_gfn(~0ULL));

This should be:

	kvm_zap_gfn_range(kvm, start, end);

>+}
>+
> /*
>  * Invalidate (zap) SPTEs that cover GFNs from gfn_start and up to gfn_end
>  * (not including it)
>-- 
>2.17.1
>