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

[Xiaoyao Li <xiaoyao.li@intel.com>]

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@vger.kernel.org
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>> 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@google.com/