Re: [PATCH v4 1/3] KVM: X86: Extend KVM_SET_VCPU_EVENTS to inject a SHUTDOWN event

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

On 3/11/2022 1:43 AM, Sean Christopherson wrote:
> On Thu, Mar 10, 2022, Chenyi Qiang wrote:
>> In some fatal case, the target vcpu would run into unexpected behavior
>> and should get shutdown (e.g. VM context is corrupted and not valid in
>> VMCS). User space would be informed in such case. To kill the target
>> vcpu, extend KVM_SET_VCPU_EVENTS ioctl to inject a synthesized SHUTDOWN
>> event with a new bit set in flags field. KVM would accordingly make
>> KVM_REQ_TRIPLE_FAULT request to trigger the real shutdown exit. Noting
>> that the KVM_REQ_TRIPLE_FAULT request also applies to the nested case,
>> so that only the target L2 vcpu would be killed.
>>
>> Signed-off-by: Chenyi Qiang <chenyi.qiang@intel.com>
>> ---
>>   Documentation/virt/kvm/api.rst  | 3 +++
>>   arch/x86/include/uapi/asm/kvm.h | 1 +
>>   arch/x86/kvm/x86.c              | 6 +++++-
>>   3 files changed, 9 insertions(+), 1 deletion(-)
>>
>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>> index 691ff84444bd..d1971ef613e7 100644
>> --- a/Documentation/virt/kvm/api.rst
>> +++ b/Documentation/virt/kvm/api.rst
>> @@ -1241,6 +1241,9 @@ can be set in the flags field to signal that the
>>   exception_has_payload, exception_payload, and exception.pending fields
>>   contain a valid state and shall be written into the VCPU.
>>   
>> +KVM_VCPUEVENT_SHUTDOWN can be set in flags field to synthesize a SHUTDOWN
>> +event for a vcpu from user space.
>> +
>>   ARM/ARM64:
>>   ^^^^^^^^^^
>>   
>> diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h
>> index bf6e96011dfe..44757bd6122d 100644
>> --- a/arch/x86/include/uapi/asm/kvm.h
>> +++ b/arch/x86/include/uapi/asm/kvm.h
>> @@ -325,6 +325,7 @@ struct kvm_reinject_control {
>>   #define KVM_VCPUEVENT_VALID_SHADOW	0x00000004
>>   #define KVM_VCPUEVENT_VALID_SMM		0x00000008
>>   #define KVM_VCPUEVENT_VALID_PAYLOAD	0x00000010
>> +#define KVM_VCPUEVENT_SHUTDOWN		0x00000020
>>   
>>   /* Interrupt shadow states */
>>   #define KVM_X86_SHADOW_INT_MOV_SS	0x01
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 4fa4d8269e5b..53c8592066c8 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -4903,7 +4903,8 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>>   			      | KVM_VCPUEVENT_VALID_SIPI_VECTOR
>>   			      | KVM_VCPUEVENT_VALID_SHADOW
>>   			      | KVM_VCPUEVENT_VALID_SMM
>> -			      | KVM_VCPUEVENT_VALID_PAYLOAD))
>> +			      | KVM_VCPUEVENT_VALID_PAYLOAD
>> +			      | KVM_VCPUEVENT_SHUTDOWN))
>>   		return -EINVAL;
>>   
>>   	if (events->flags & KVM_VCPUEVENT_VALID_PAYLOAD) {
>> @@ -4976,6 +4977,9 @@ static int kvm_vcpu_ioctl_x86_set_vcpu_events(struct kvm_vcpu *vcpu,
>>   		}
>>   	}
>>   
>> +	if (events->flags & KVM_VCPUEVENT_SHUTDOWN)
>> +		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
> 
> Huh.  I think we need to make this bidirection and add it to get_vcpu_events()
> as well, and treat it as a bug fix.  In direct triple fault cases, i.e. hardware
> detected and morphed to VM-Exit, KVM will never lose the triple fault.  But for
> triple faults sythesized by KVM, e.g. the RSM path or nested_vmx_abort(), if KVM
> exits to userspace before the request is serviced, userspace could migrate the
> VM and lose the triple fault.

Good catch. Then the name of this definition is not quit fit now. How 
about changing to KVM_VCPUEVENT_SYTHESIZED_TRIPLE_FAULT?