linux-kernel - [PATCH 6/9] KVM: x86/mmu: Print SPTEs on unexpected #VE

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Date: Fri, 17 May 2024 17:04:27 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 6/9] KVM: x86/mmu: Print SPTEs on unexpected #VE

Print the SPTEs that correspond to the faulting GPA on an unexpected EPT
Violation #VE to help the user debug failures, e.g. to pinpoint which SPTE
didn't have SUPPRESS_VE set.

Opportunistically assert that the underlying exit reason was indeed an EPT
Violation, as the CPU has *really* gone off the rails if a #VE occurs due
to a completely unexpected exit reason.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/mmu/mmu.c          | 42 ++++++++++++++++++++++++++-------
 arch/x86/kvm/vmx/vmx.c          |  5 ++++
 3 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index aabf1648a56a..9bb2e164c523 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2159,6 +2159,7 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu);
 
 int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 		       void *insn, int insn_len);
+void kvm_mmu_print_sptes(struct kvm_vcpu *vcpu, gpa_t gpa, const char *msg);
 void kvm_mmu_invlpg(struct kvm_vcpu *vcpu, gva_t gva);
 void kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 			     u64 addr, unsigned long roots);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d2af077d8b34..f2c9580d9588 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -4124,6 +4124,22 @@ static int get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes, int *root_level
 	return leaf;
 }
 
+static int get_sptes_lockless(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes,
+			      int *root_level)
+{
+	int leaf;
+
+	walk_shadow_page_lockless_begin(vcpu);
+
+	if (is_tdp_mmu_active(vcpu))
+		leaf = kvm_tdp_mmu_get_walk(vcpu, addr, sptes, root_level);
+	else
+		leaf = get_walk(vcpu, addr, sptes, root_level);
+
+	walk_shadow_page_lockless_end(vcpu);
+	return leaf;
+}
+
 /* return true if reserved bit(s) are detected on a valid, non-MMIO SPTE. */
 static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
 {
@@ -4132,15 +4148,7 @@ static bool get_mmio_spte(struct kvm_vcpu *vcpu, u64 addr, u64 *sptep)
 	int root, leaf, level;
 	bool reserved = false;
 
-	walk_shadow_page_lockless_begin(vcpu);
-
-	if (is_tdp_mmu_active(vcpu))
-		leaf = kvm_tdp_mmu_get_walk(vcpu, addr, sptes, &root);
-	else
-		leaf = get_walk(vcpu, addr, sptes, &root);
-
-	walk_shadow_page_lockless_end(vcpu);
-
+	leaf = get_sptes_lockless(vcpu, addr, sptes, &root);
 	if (unlikely(leaf < 0)) {
 		*sptep = 0ull;
 		return reserved;
@@ -5963,6 +5971,22 @@ int noinline kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 err
 }
 EXPORT_SYMBOL_GPL(kvm_mmu_page_fault);
 
+void kvm_mmu_print_sptes(struct kvm_vcpu *vcpu, gpa_t gpa, const char *msg)
+{
+	u64 sptes[PT64_ROOT_MAX_LEVEL + 1];
+	int root_level, leaf, level;
+
+	leaf = get_sptes_lockless(vcpu, gpa, sptes, &root_level);
+	if (unlikely(leaf < 0))
+		return;
+
+	pr_err("%s %llx", msg, gpa);
+	for (level = root_level; level >= leaf; level--)
+		pr_cont(", spte[%d] = 0x%llx", level, sptes[level]);
+	pr_cont("\n");
+}
+EXPORT_SYMBOL_GPL(kvm_mmu_print_sptes);
+
 static void __kvm_mmu_invalidate_addr(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 				      u64 addr, hpa_t root_hpa)
 {
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 0c68643d982b..2a3fce61c785 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5218,7 +5218,12 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 		return handle_ud(vcpu);
 
 	if (KVM_BUG_ON(is_ve_fault(intr_info), vcpu->kvm)) {
+		struct vmx_ve_information *ve_info = vmx->ve_info;
+
+		WARN_ONCE(ve_info->exit_reason != EXIT_REASON_EPT_VIOLATION,
+			  "Unexpected #VE on VM-Exit reason 0x%x", ve_info->exit_reason);
 		dump_vmcs(vcpu);
+		kvm_mmu_print_sptes(vcpu, ve_info->guest_physical_address, "#VE");
 		return -EIO;
 	}
 
-- 
2.45.0.215.g3402c0e53f-goog