linux-kernel - [PATCH 19/22] KVM: x86: Update retry protection fields when forcing retry on emulation failure

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Message-ID: <20240809190319.1710470-20-seanjc@google.com>
Date: Fri,  9 Aug 2024 12:03:16 -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, 
	Peter Gonda <pgonda@...gle.com>, Michael Roth <michael.roth@....com>, 
	Vishal Annapurve <vannapurve@...gle.com>, Ackerly Tng <ackerleytng@...gle.com>
Subject: [PATCH 19/22] KVM: x86: Update retry protection fields when forcing
 retry on emulation failure

When retrying the faulting instruction after emulation failure, refresh
the infinite loop protection fields even if no shadow pages were zapped,
i.e. avoid hitting an infinite loop even when retrying the instruction as
a last-ditch effort to avoid terminating the guest.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/include/asm/kvm_host.h | 10 +++++++++-
 arch/x86/kvm/mmu/mmu.c          | 12 +++++++-----
 arch/x86/kvm/x86.c              |  2 +-
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 25a3d84ca5e2..b3a2793fc89c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -2132,7 +2132,15 @@ int kvm_get_nr_pending_nmis(struct kvm_vcpu *vcpu);
 void kvm_update_dr7(struct kvm_vcpu *vcpu);
 
 int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn);
-bool kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa);
+bool __kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
+				       bool always_retry);
+
+static inline bool kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu,
+						   gpa_t cr2_or_gpa)
+{
+	return __kvm_mmu_unprotect_gfn_and_retry(vcpu, cr2_or_gpa, false);
+}
+
 void kvm_mmu_free_roots(struct kvm *kvm, struct kvm_mmu *mmu,
 			ulong roots_to_free);
 void kvm_mmu_free_guest_mode_roots(struct kvm *kvm, struct kvm_mmu *mmu);
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d3c0220ff7ee..59af085a6e8e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2731,22 +2731,24 @@ int kvm_mmu_unprotect_page(struct kvm *kvm, gfn_t gfn)
 	return r;
 }
 
-bool kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa)
+bool __kvm_mmu_unprotect_gfn_and_retry(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
+				       bool always_retry)
 {
 	gpa_t gpa = cr2_or_gpa;
-	bool r;
+	bool r = false;
 
 	if (!vcpu->kvm->arch.indirect_shadow_pages)
-		return false;
+		goto out;
 
 	if (!vcpu->arch.mmu->root_role.direct) {
 		gpa = kvm_mmu_gva_to_gpa_write(vcpu, cr2_or_gpa, NULL);
 		if (gpa == INVALID_GPA)
-			return false;
+			goto out;
 	}
 
 	r = kvm_mmu_unprotect_page(vcpu->kvm, gpa_to_gfn(gpa));
-	if (r) {
+out:
+	if (r || always_retry) {
 		vcpu->arch.last_retry_eip = kvm_rip_read(vcpu);
 		vcpu->arch.last_retry_addr = cr2_or_gpa;
 	}
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ddeda91b0530..65531768bb1e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8888,7 +8888,7 @@ static bool reexecute_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
 	 * guest to let the CPU re-execute the instruction in the hope that the
 	 * CPU can cleanly execute the instruction that KVM failed to emulate.
 	 */
-	kvm_mmu_unprotect_gfn_and_retry(vcpu, cr2_or_gpa);
+	__kvm_mmu_unprotect_gfn_and_retry(vcpu, cr2_or_gpa, true);
 
 	/*
 	 * Retry even if _this_ vCPU didn't unprotect the gfn, as it's possible
-- 
2.46.0.76.ge559c4bf1a-goog