Re: [PATCH v2 2/3] KVM: TDX: Fix the exit reason handling

On 8/11/2026 8:04 AM, Sean Christopherson wrote:
> On Mon, Aug 10, 2026, Sean Christopherson wrote:
>> On Mon, Aug 10, 2026, Xiaoyao Li wrote:
>>> On 8/10/2026 7:39 PM, [email protected] wrote:
>>>>> @@ -2147,7 +2156,7 @@ void tdx_get_exit_info(struct kvm_vcpu *vcpu, u32 *reason,
>>>>>    	struct vcpu_tdx *tdx = to_tdx(vcpu);
>>>>>    	*reason = tdx->vt.exit_reason.full;
>>>>> -	if (*reason != -1u) {
>>>>> +	if (tdx->vt.exit_reason.basic != -1) {
>>>> [Severity: Medium]
>>>> Will this check always evaluate to true due to C integer promotion rules?
>>>>
>>>> The basic field in union vmx_exit_reason is a 16-bit unsigned bitfield. When
>>>> comparing it to -1, the unsigned 16-bit value is promoted to a signed 32-bit
>>>> integer. If the value was set to -1 (65535), the comparison evaluates as
>>>> 65535 != -1, which is always true.
>>>>
>>>
>>> Well, how about something below on top of this patch?
>>
>> No, we need to not rely on magic exit_reason.basic values.  Can't this be?
>>
>> 	if ((tdx->vp_enter_ret & TDX_SW_ERROR) != TDX_SW_ERROR) {
> 
> This would arguably be a bug fix as well, because the "real" EXIT_REASON_EPT_MISCONFIG
> path gets a false negative.  E.g. when getting information for an EPT Misconfig
> for the tracepoint, KVM really should print all information, not zeros.
> 
> At a glance, this exact change can probably be a separate patch too.

Yeah, this issue can be fixed by the patch which turns real 
EPT_MISCONFIG to TDX_SW_ERROR.

Side topic, tdx_to_vmx_exit_reason() can change EXIT_REASON_TDCALL to 
other Exit Reason. Do we want to print TDCALL instead of the transformed 
reason here?

>> 		<read values>
>> 	} else {
>> 		<zero values>
>> 	}
>>
>> We'd need to use the unsafe version if we go with my suggestion[*], but other
>> than that wrinkle, the above seems like the obviously correct fix (maybe too
>> obvious)?
>>
>> [*] https://lore.kernel.org/all/[email protected]