linux-kernel - [PATCH 3/4] KVM: x86/mmu: Make sure pfn is not changed for spurious fault

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Message-ID: <20250207030900.1808-1-yan.y.zhao@intel.com>
Date: Fri,  7 Feb 2025 11:09:00 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: pbonzini@...hat.com,
	seanjc@...gle.com
Cc: rick.p.edgecombe@...el.com,
	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	Yan Zhao <yan.y.zhao@...el.com>
Subject: [PATCH 3/4] KVM: x86/mmu: Make sure pfn is not changed for spurious fault

Make sure pfn is not changed for a spurious fault by warning in the TDP
MMU. For shadow path, only treat a prefetch fault as spurious when pfn is
not changed, since the rmap removal and add are required when pfn is
changed.

Cc: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Yan Zhao <yan.y.zhao@...el.com>
---
 arch/x86/kvm/mmu/mmu.c     | 3 ++-
 arch/x86/kvm/mmu/tdp_mmu.c | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 3d74e680006f..47fd3712afe6 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2846,7 +2846,8 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, struct kvm_memory_slot *slot,
 	}
 
 	if (is_shadow_present_pte(*sptep)) {
-		if (prefetch && is_last_spte(*sptep, level))
+		if (prefetch && is_last_spte(*sptep, level) &&
+		    pfn == spte_to_pfn(*sptep))
 			return RET_PF_SPURIOUS;
 
 		/*
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 5f9e7374220e..8b37e4f542f3 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -1139,7 +1139,8 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
 
 	if (is_shadow_present_pte(iter->old_spte) &&
 	    is_access_allowed(fault, iter->old_spte) &&
-	    is_last_spte(iter->old_spte, iter->level))
+	    is_last_spte(iter->old_spte, iter->level) &&
+	    !WARN_ON_ONCE(fault->pfn != spte_to_pfn(iter->old_spte)))
 		return RET_PF_SPURIOUS;
 
 	if (unlikely(!fault->slot))
-- 
2.43.2