Re: [PATCH v7 1/2] i386: kvm: extend kvm_{get, put}_vcpu_events to support pending triple fault

[Chenyi Qiang <chenyi.qiang@intel.com>]

On 9/27/2022 9:14 PM, Paolo Bonzini wrote:
> On 9/23/22 09:33, Chenyi Qiang wrote:
>> For the direct triple faults, i.e. hardware detected and KVM morphed
>> to VM-Exit, KVM will never lose them. But for triple faults sythesized
>> by KVM, e.g. the RSM path, if KVM exits to userspace before the request
>> is serviced, userspace could migrate the VM and lose the triple fault.
>>
>> A new flag KVM_VCPUEVENT_VALID_TRIPLE_FAULT is defined to signal that
>> the event.triple_fault_pending field contains a valid state if the
>> KVM_CAP_X86_TRIPLE_FAULT_EVENT capability is enabled.
> 
> Note that you are not transmitting the field on migration.  You need
> this on top:
> 
> diff --git a/target/i386/cpu.h b/target/i386/cpu.h
> index b97d182e28..d4124973ce 100644
> --- a/target/i386/cpu.h
> +++ b/target/i386/cpu.h
> @@ -1739,7 +1739,7 @@ typedef struct CPUArchState {
>       uint8_t has_error_code;
>       uint8_t exception_has_payload;
>       uint64_t exception_payload;
> -    bool triple_fault_pending;
> +    uint8_t triple_fault_pending;
>       uint32_t ins_len;
>       uint32_t sipi_vector;
>       bool tsc_valid;
> diff --git a/target/i386/machine.c b/target/i386/machine.c
> index cecd476e98..310b125235 100644
> --- a/target/i386/machine.c
> +++ b/target/i386/machine.c
> @@ -1562,6 +1562,25 @@ static const VMStateDescription vmstate_arch_lbr = {
>       }
>   };
> 
> +static bool triple_fault_needed(void *opaque)
> +{
> +    X86CPU *cpu = opaque;
> +    CPUX86State *env = &cpu->env;
> +
> +    return env->triple_fault_pending;
> +}
> +
> +static const VMStateDescription vmstate_triple_fault = {
> +    .name = "cpu/triple_fault",
> +    .version_id = 1,
> +    .minimum_version_id = 1,
> +    .needed = triple_fault_needed,
> +    .fields = (VMStateField[]) {
> +        VMSTATE_UINT8(env.triple_fault_pending, X86CPU),
> +        VMSTATE_END_OF_LIST()
> +    }
> +};
> +
>   const VMStateDescription vmstate_x86_cpu = {
>       .name = "cpu",
>       .version_id = 12,
> @@ -1706,6 +1725,7 @@ const VMStateDescription vmstate_x86_cpu = {
>           &vmstate_amx_xtile,
>   #endif
>           &vmstate_arch_lbr,
> +        &vmstate_triple_fault,
>           NULL
>       }
>   };

Thanks Paolo for your review!

I'll add this in next version.

>