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

[Xiaoyao Li]

On 8/11/2026 8:38 AM, Edgecombe, Rick P wrote:
> On Mon, 2026-08-10 at 19:21 +0800, Xiaoyao Li wrote:
> > Get and check the exit reason from the low 16 bits of vp_enter_ret, and
> > store the synthesized/transformed exit reason in the "basic" field.
> >
> > Some bits in the upper 16 bits in the exit reason have their own meanings
> > and they might be 1.  When handling the exit reason, only do handling on
> > the lower 16 bits and keep the upper 16 bits unchanged.  This change
> > also helps remove the additional check in tdx_failed_vmentry().
> >
> > Note, due to the synthesized invalid exit reason, -1, is changed to
> > assigned to the "basic" field, adjust the checking in tdx_get_exit_info()
> > accordingly.
> >
> > Fixes: 095b71a03f49 ("KVM: TDX: Add a place holder to handle TDX VM exit")
> > Fixes: c42856af8f70 ("KVM: TDX: Add a place holder for handler of TDX hypercalls (TDG.VP.VMCALL)")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> > ---
> > Changes in v2:
> >   - new patch
> > ---
> >   arch/x86/kvm/vmx/tdx.c | 35 ++++++++++++++++++++++-------------
> >   1 file changed, 22 insertions(+), 13 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > index 7338ac0af693..a89885d550c9 100644
> > --- a/arch/x86/kvm/vmx/tdx.c
> > +++ b/arch/x86/kvm/vmx/tdx.c
> > @@ -921,10 +921,10 @@ static __always_inline u32 tdcall_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
> >   	return EXIT_REASON_TDCALL;
> >   }
> >   
> > -static __always_inline u32 tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
> > +static __always_inline union vmx_exit_reason tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
> >   {
> >   	struct vcpu_tdx *tdx = to_tdx(vcpu);
> > -	u32 exit_reason;
> > +	union vmx_exit_reason exit_reason;
> >   
> >   	switch (tdx->vp_enter_ret & TDX_SEAMCALL_STATUS_MASK) {
> >   	case TDX_SUCCESS:
> > @@ -934,23 +934,33 @@ static __always_inline u32 tdx_to_vmx_exit_reason(struct kvm_vcpu *vcpu)
> >   	case TDX_NON_RECOVERABLE_TD_WRONG_APIC_MODE:
> >   		break;
> >   	default:
> > -		return -1u;
> > +		/*
> > +		 * Synthesize an invalid bogus Exit Reason, as the TDX-Module
>
> I think this blurb came from Sean, but can we standardize on "TDX module"? The
> code currently uses "TDX module" and "TDX-module" and "TDX-module" used much
> less. I also don't see why it needs the "-".

Will change it to "TDX module".

> > +		 * never attempted to run the vCPU, i.e. the Exit Reason is
> > +		 * undefined, but this is NOT a failed VM-Enter.
> > +		 */
> > +		return (union vmx_exit_reason) {
> > +			.basic = -1,
> > +		};
> >   	}
> >   
> > -	exit_reason = tdx->vp_enter_ret;
> > +	exit_reason.full = (u32)tdx->vp_enter_ret;
> >   
> > -	switch (exit_reason) {
> > +	switch (exit_reason.basic) {
> >   	case EXIT_REASON_TDCALL:
> >   		if (tdvmcall_exit_type(vcpu))
> > -			return EXIT_REASON_VMCALL;
> > -
> > -		return tdcall_to_vmx_exit_reason(vcpu);
> > +			exit_reason.basic = EXIT_REASON_VMCALL;
> > +		else
> > +			exit_reason.basic = tdcall_to_vmx_exit_reason(vcpu);
> > +		break;
> >   	case EXIT_REASON_EPT_MISCONFIG:
> >   		/*
> >   		 * Defer KVM_BUG_ON() until tdx_handle_exit() because this is in
> >   		 * non-instrumentable code with interrupts disabled.
> >   		 */
> > -		return -1u;
> > +		return (union vmx_exit_reason) {
> > +			.basic = -1,
> > +		};
>
> We could make this return instead be a goto err; that returns this. Bonus is the
> comment on the other one can cover them both. What do you think?

Given 1) this patch is here mainly to avoid the false-positive on 
bus_lock_detected after the next patch, 2) the whole series is targeted 
for stable kernels, and 3) this part will change as suggested by [1]

I think we can just leave it as-is to make the change as simple as possible.

[1] https://lore.kernel.org/all/anXxBzO41_5eaaOI@xxxxxxxxxx/