linux-kernel - Re: [PATCH v19 101/130] KVM: TDX: handle ept violation/misconfig exit

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Message-ID: <Zgoz0sizgEZhnQ98@chao-email>
Date: Mon, 1 Apr 2024 12:10:58 +0800
From: Chao Gao <chao.gao@...el.com>
To: <isaku.yamahata@...el.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<isaku.yamahata@...il.com>, Paolo Bonzini <pbonzini@...hat.com>,
	<erdemaktas@...gle.com>, Sean Christopherson <seanjc@...gle.com>, Sagi Shahar
	<sagis@...gle.com>, Kai Huang <kai.huang@...el.com>, <chen.bo@...el.com>,
	<hang.yuan@...el.com>, <tina.zhang@...el.com>
Subject: Re: [PATCH v19 101/130] KVM: TDX: handle ept violation/misconfig exit

>+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) {

Unless the CPU has a bug, instruction fetch in TD from shared memory causes a
#PF. I think you can add a comment for this.

Maybe KVM_BUG_ON() is more appropriate as it signifies a potential bug.

>+			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(vcpu, 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_ONCE(1);
>+
>+	vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
>+	vcpu->run->internal.suberror = KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
>+	vcpu->run->internal.ndata = 2;
>+	vcpu->run->internal.data[0] = EXIT_REASON_EPT_MISCONFIG;
>+	vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
>+
>+	return 0;
>+}
>+
> int tdx_handle_exit(struct kvm_vcpu *vcpu, fastpath_t fastpath)
> {
> 	union tdx_exit_reason exit_reason = to_tdx(vcpu)->exit_reason;
>@@ -1345,6 +1390,10 @@ 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);

Handling EPT misconfiguration can be dropped because the "default" case handles
all unexpected exits in the same way


> 	case EXIT_REASON_OTHER_SMI:
> 		/*
> 		 * If reach here, it's not a Machine Check System Management
>-- 
>2.25.1
>
>