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

Chao Gao
2024-04-01T04:11:12Z

>+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
>
>