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

[Sean Christopherson <seanjc@google.com>]

On Mon, Aug 10, 2026, Xiaoyao Li wrote:
> On 8/10/2026 7:39 PM, sashiko-bot@kernel.org 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) {
		<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/anXxBzO41_5eaaOI@google.com