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

Reinette Chatre
2024-04-30T20:49:04Z

Hi Isaku,

On 4/3/2024 11:42 AM, Isaku Yamahata wrote:
> On Mon, Apr 01, 2024 at 12:10:58PM +0800,
> Chao Gao <chao.gao@intel.com> wrote:
>
>>> +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.
>
> Yes.
>
>
>> Maybe KVM_BUG_ON() is more appropriate as it signifies a potential bug.
>
> Bug of what component? CPU. If so, I think KVM_EXIT_INTERNAL_ERROR +
> KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON is more appropriate.
>

Is below what you have in mind?

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 499c6cd9633f..bd30b4c4d710 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -1305,11 +1305,18 @@ static int tdx_handle_ept_violation(struct kvm_vcpu *vcpu)
} else {
exit_qual = tdexit_exit_qual(vcpu);
if (exit_qual & EPT_VIOLATION_ACC_INSTR) {
+ /*
+ * Instruction fetch in TD from shared memory
+ * causes a #PF.
+ */
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;
+ 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_VIOLATION;
+ vcpu->run->internal.data[1] = vcpu->arch.last_vmentry_cpu;
return 0;
}
}

Thank you

Reinette