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From:   isaku.yamahata@intel.com
To:     kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     isaku.yamahata@intel.com, isaku.yamahata@gmail.com,
        Paolo Bonzini <pbonzini@redhat.com>, erdemaktas@google.com,
        Sean Christopherson <seanjc@google.com>,
        Sagi Shahar <sagis@google.com>
Subject: [RFC PATCH v6 086/104] KVM: TDX: handle ept violation/misconfig exit
Date:   Thu,  5 May 2022 11:15:20 -0700
Message-Id: <b5527f06a64678b260196ea67386c98be32f43dd.1651774250.git.isaku.yamahata@intel.com>
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From: Isaku Yamahata <isaku.yamahata@intel.com>

On EPT violation, call a common function, __vmx_handle_ept_violation() to
trigger x86 MMU code.  On EPT misconfiguration, exit to ring 3 with
KVM_EXIT_UNKNOWN.  because EPT misconfiguration can't happen as MMIO is
trigged by TDG.VP.VMCALL. No point to set a misconfiguration value for the
fast path.

Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
---
 arch/x86/kvm/vmx/tdx.c | 46 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 1f31dead31f2..82bfdb05e67b 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1191,6 +1191,48 @@ void tdx_deliver_interrupt(struct kvm_lapic *apic, int delivery_mode,
 	__vmx_deliver_posted_interrupt(vcpu, &tdx->pi_desc, vector);
 }
 
+static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
+{
+	unsigned long exit_qual;
+
+	if (kvm_is_private_gpa(vcpu->kvm, tdexit_gpa(vcpu))) {
+		/*
+		 * Always treat SEPT violations as write faults.  Ignore the
+		 * EXIT_QUALIFICATION reported by TDX-SEAM for SEPT violations.
+		 * TD private pages are always RWX in the SEPT tables,
+		 * i.e. they're always mapped writable.  Just as importantly,
+		 * treating SEPT violations as write faults is necessary to
+		 * avoid COW allocations, which will cause TDAUGPAGE failures
+		 * due to aliasing a single HPA to multiple GPAs.
+		 */
+#define TDX_SEPT_VIOLATION_EXIT_QUAL	EPT_VIOLATION_ACC_WRITE
+		exit_qual = TDX_SEPT_VIOLATION_EXIT_QUAL;
+	} else {
+		exit_qual = tdexit_exit_qual(vcpu);;
+		if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
+			pr_warn("kvm: TDX instr fetch to shared GPA = 0x%lx @ RIP = 0x%lx\n",
+				tdexit_gpa(vcpu), kvm_rip_read(vcpu));
+			vcpu->run->exit_reason = KVM_EXIT_EXCEPTION;
+			vcpu->run->ex.exception = PF_VECTOR;
+			vcpu->run->ex.error_code = exit_qual;
+			return 0;
+		}
+	}
+
+	trace_kvm_page_fault(tdexit_gpa(vcpu), exit_qual);
+	return __vmx_handle_ept_violation(vcpu, tdexit_gpa(vcpu), exit_qual);
+}
+
+static int tdx_handle_ept_misconfig(struct kvm_vcpu *vcpu)
+{
+	WARN_ON(1);
+
+	vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
+	vcpu->run->hw.hardware_exit_reason = EXIT_REASON_EPT_MISCONFIG;
+
+	return 0;
+}
+
 int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
 {
 	union tdx_exit_reason exit_reason = to_tdx(vcpu)->exit_reason;
@@ -1209,6 +1251,10 @@ int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
 	WARN_ON_ONCE(fastpath != EXIT_FASTPATH_NONE);
 
 	switch (exit_reason.basic) {
+	case EXIT_REASON_EPT_VIOLATION:
+		return tdx_handle_ept_violation(vcpu);
+	case EXIT_REASON_EPT_MISCONFIG:
+		return tdx_handle_ept_misconfig(vcpu);
 	case EXIT_REASON_OTHER_SMI:
 		/*
 		 * If reach here, it's not a Machine Check System Management
-- 
2.25.1