Re: [PATCH 4/7] KVM: SVM: Populate FRED event data on event injection

[Shivansh Dhiman]

Hey Paolo,

On 06-03-2026 17:01, Paolo Bonzini wrote:
> On 1/29/26 07:36, Shivansh Dhiman wrote:
>> From: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
>>
>> Set injected-event data (in EVENTINJDATA) when injecting an event,
>> use EXITINTDATA for populating the injected-event data during
>> reinjection.
>>
>> Unlike IDT using some extra CPU register as part of an event
>> context, e.g., %cr2 for #PF, FRED saves a complete event context
>> in its stack frame, e.g., FRED saves the faulting linear address
>> of a #PF into the event data field defined in its stack frame.
>>
>> Populate the EVENTINJDATA during event injection. The event data
>> will be pushed into a FRED stack frame for VM entries that inject
>> an event using FRED event delivery.
>>
>> Signed-off-by: Neeraj Upadhyay <Neeraj.Upadhyay@xxxxxxx>
>> Co-developed-by: Shivansh Dhiman <shivansh.dhiman@xxxxxxx>
>> Signed-off-by: Shivansh Dhiman <shivansh.dhiman@xxxxxxx>
>> ---
>>   arch/x86/kvm/svm/svm.c | 22 ++++++++++++++++++----
>>   1 file changed, 18 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
>> index ddd8941af6f0..693b46d715b4 100644
>> --- a/arch/x86/kvm/svm/svm.c
>> +++ b/arch/x86/kvm/svm/svm.c
>> @@ -374,6 +374,10 @@ static void svm_inject_exception(struct kvm_vcpu *vcpu)
>>               | SVM_EVTINJ_VALID
>>               | (ex->has_error_code ? SVM_EVTINJ_VALID_ERR : 0)
>>               | SVM_EVTINJ_TYPE_EXEPT;
>> +
>> +     if (is_fred_enabled(vcpu))
>> +             svm->vmcb->control.event_inj_data = ex->event_data;
>> +
>>       svm->vmcb->control.event_inj_err = ex->error_code;
>>   }
>>
>> @@ -4066,7 +4070,7 @@ static void svm_complete_soft_interrupt(struct kvm_vcpu *vcpu, u8 vector,
>>               kvm_rip_write(vcpu, svm->soft_int_old_rip);
>>   }
>>
>> -static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
>> +static void svm_complete_interrupts(struct kvm_vcpu *vcpu, bool reinject_on_vmexit)
>>   {
>>       struct vcpu_svm *svm = to_svm(vcpu);
>>       u8 vector;
>> @@ -4111,6 +4115,7 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
>>               break;
>>       case SVM_EXITINTINFO_TYPE_EXEPT: {
>>               u32 error_code = 0;
>> +             u64 event_data = 0;
>>
>>               /*
>>                * Never re-inject a #VC exception.
>> @@ -4121,9 +4126,18 @@ static void svm_complete_interrupts(struct kvm_vcpu *vcpu)
>>               if (exitintinfo & SVM_EXITINTINFO_VALID_ERR)
>>                       error_code = svm->vmcb->control.exit_int_info_err;
>>
>> +             /*
>> +              * FRED requires an additional field to pass injected-event
>> +              * data to the guest.
>> +              */
>> +             if (is_fred_enabled(vcpu) && (vector == PF_VECTOR || vector == DB_VECTOR))
>> +                     event_data = reinject_on_vmexit ?
>> +                                     svm->vmcb->control.exit_int_data :
>> +                                     svm->vmcb->control.event_inj_data;
> 
> The new argument is not needed, just...

Agreed. That'll simplify this to:

        if (is_fred_enabled(vcpu) && (vector == PF_VECTOR || vector == DB_VECTOR))
                event_data = svm->vmcb->control.exit_int_data;

> 
>> @@ -4146,7 +4160,7 @@ static void svm_cancel_injection(struct kvm_vcpu *vcpu)
>>       control->exit_int_info = control->event_inj;
>>       control->exit_int_info_err = control->event_inj_err;
> 
> ... move event_inj into exit_int here, similar to the other fields:
> 
>        control->exit_int_data = control->event_inj_data;

Ack.

- Shivansh

> 
> Paolo
> 
>>       control->event_inj = 0;
>> -     svm_complete_interrupts(vcpu);
>> +     svm_complete_interrupts(vcpu, false);
>>   }
>>
>>   static int svm_vcpu_pre_run(struct kvm_vcpu *vcpu)
>> @@ -4382,7 +4396,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu, u64 run_flags)
>>
>>       trace_kvm_exit(vcpu, KVM_ISA_SVM);
>>
>> -     svm_complete_interrupts(vcpu);
>> +     svm_complete_interrupts(vcpu, true);
>>
>>       return svm_exit_handlers_fastpath(vcpu);
>>   }
>