linux-kernel - [PATCH] KVM: VMX: Always reflect SGX EPCM #PFs back into the guest

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Message-ID: <20251121222018.348987-1-seanjc@google.com>
Date: Fri, 21 Nov 2025 14:20:18 -0800
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, 
	Kai Huang <kai.huang@...el.com>
Subject: [PATCH] KVM: VMX: Always reflect SGX EPCM #PFs back into the guest

When handling intercepted #PFs, reflect EPCM (Enclave Page Cache Map)
violations, i.e. #PFs with the SGX flag set, back into the guest.  KVM
doesn't shadow EPCM entries (the EPCM deals only with virtual/linear
addresses), and so EPCM violation cannot be due to KVM interference,
and more importantly can't be resolved by KVM.

On pre-SGX2 hardware, EPCM violations are delivered as #GP(0) faults, but
on SGX2+ hardware, they are delivered as #PF(SGX).  Failure to account for
the SGX2 behavior could put a vCPU into an infinite loop due to KVM not
realizing the #PF is the guest's responsibility.

Take care to deliver the EPCM violation as a #GP(0) if the _guest_ CPU
model is only SGX1.

Fixes: 72add915fbd5 ("KVM: VMX: Enable SGX virtualization for SGX1, SGX2 and LC")
Cc: Kai Huang <kai.huang@...el.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---

SGX side of things is compile tested only.

 arch/x86/kvm/vmx/vmx.c | 58 ++++++++++++++++++++++++++++++++----------
 1 file changed, 44 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 4cbe8c84b636..7c4080d780b5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5303,12 +5303,53 @@ static bool is_xfd_nm_fault(struct kvm_vcpu *vcpu)
 	       !kvm_is_cr0_bit_set(vcpu, X86_CR0_TS);
 }
 
+static int vmx_handle_page_fault(struct kvm_vcpu *vcpu, u32 error_code)
+{
+	unsigned long cr2 = vmx_get_exit_qual(vcpu);
+
+	if (vcpu->arch.apf.host_apf_flags)
+		goto handle_pf;
+
+	/* When using EPT, KVM intercepts #PF only to detect illegal GPAs. */
+	WARN_ON_ONCE(enable_ept && !allow_smaller_maxphyaddr);
+
+	/*
+	 * On SGX2 hardware, EPCM violations are delivered as #PF with the SGX
+	 * flag set in the error code (SGX1 hardware generates #GP(0)).  EPCM
+	 * violations have nothing to do with shadow paging and can never be
+	 * resolved by KVM; always reflect them into the guest.
+	 */
+	if (error_code & PFERR_SGX_MASK) {
+		WARN_ON_ONCE(!IS_ENABLED(CONFIG_X86_SGX_KVM) ||
+			     !cpu_feature_enabled(X86_FEATURE_SGX2));
+
+		if (guest_cpu_cap_has(vcpu, X86_FEATURE_SGX2))
+			kvm_fixup_and_inject_pf_error(vcpu, cr2, error_code);
+		else
+			kvm_inject_gp(vcpu, 0);
+		return 1;
+	}
+
+	/*
+	 * If EPT is enabled, fixup and inject the #PF.  KVM intercepts #PFs
+	 * only to set PFERR_RSVD as appropriate (hardware won't set RSVD due
+	 * to the GPA being legal with respect to host.MAXPHYADDR).
+	 */
+	if (enable_ept) {
+		kvm_fixup_and_inject_pf_error(vcpu, cr2, error_code);
+		return 1;
+	}
+
+handle_pf:
+	return kvm_handle_page_fault(vcpu, error_code, cr2, NULL, 0);
+}
+
 static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 {
 	struct vcpu_vmx *vmx = to_vmx(vcpu);
 	struct kvm_run *kvm_run = vcpu->run;
 	u32 intr_info, ex_no, error_code;
-	unsigned long cr2, dr6;
+	unsigned long dr6;
 	u32 vect_info;
 
 	vect_info = vmx->idt_vectoring_info;
@@ -5383,19 +5424,8 @@ static int handle_exception_nmi(struct kvm_vcpu *vcpu)
 		return 0;
 	}
 
-	if (is_page_fault(intr_info)) {
-		cr2 = vmx_get_exit_qual(vcpu);
-		if (enable_ept && !vcpu->arch.apf.host_apf_flags) {
-			/*
-			 * EPT will cause page fault only if we need to
-			 * detect illegal GPAs.
-			 */
-			WARN_ON_ONCE(!allow_smaller_maxphyaddr);
-			kvm_fixup_and_inject_pf_error(vcpu, cr2, error_code);
-			return 1;
-		} else
-			return kvm_handle_page_fault(vcpu, error_code, cr2, NULL, 0);
-	}
+	if (is_page_fault(intr_info))
+		return vmx_handle_page_fault(vcpu, error_code);
 
 	ex_no = intr_info & INTR_INFO_VECTOR_MASK;
 

base-commit: 0c3b67dddd1051015f5504389a551ecd260488a5
-- 
2.52.0.rc2.455.g230fcf2819-goog