[PATCH 3/3] KVM: x86/mmu: Reword a misleading comment about checking gpte_changed()
From: Sean Christopherson
Date: Fri Aug 02 2024 - 16:39:54 EST
Rewrite the comment in FNAME(fetch) to explain why KVM needs to check that
the gPTE is still fresh before continuing the shadow page walk, even if
KVM already has a linked shadow page for the gPTE in question.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/paging_tmpl.h | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 480c54122991..405bd7ceee2a 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -695,8 +695,14 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
return RET_PF_RETRY;
/*
- * Verify that the gpte in the page we've just write
- * protected is still there.
+ * Verify that the gpte in the page, which is now either
+ * write-protected or unsync, wasn't modified between the fault
+ * and acquiring mmu_lock. This needs to be done even when
+ * reusing an existing shadow page to ensure the information
+ * gathered by the walker matches the information stored in the
+ * shadow page (which could have been modified by a different
+ * vCPU even if the page was already linked). Holding mmu_lock
+ * prevents the shadow page from changing after this point.
*/
if (FNAME(gpte_changed)(vcpu, gw, it.level - 1))
return RET_PF_RETRY;
--
2.46.0.rc2.264.g509ed76dc8-goog