Re: [PATCH] kvm/i386: Set proper nested state format for SVM

[Paolo Bonzini <pbonzini@redhat.com>]

On 16/11/20 19:25, Tom Lendacky wrote:
> On 11/16/20 12:09 PM, Paolo Bonzini wrote:
>> On 16/11/20 18:02, Tom Lendacky wrote:
>>> From: Tom Lendacky<thomas.lendacky@amd.com>
>>>
>>> Currently, the nested state format is hardcoded to VMX. This will result
>>> in kvm_put_nested_state() returning an error because the KVM SVM support
>>> checks for the nested state to be KVM_STATE_NESTED_FORMAT_SVM. As a
>>> result, kvm_arch_put_registers() errors out early.
>>>
>>> Update the setting of the format based on the virtualization feature:
>>>     VMX - KVM_STATE_NESTED_FORMAT_VMX
>>>     SVM - KVM_STATE_NESTED_FORMAT_SVM
>>
>> Looks good, but what are the symptoms of this in practice?
> 
> I discovered this while testing my SEV-ES patches. When I specified the
> '+svm' feature, the new SEV-ES reset address for the APs wasn't getting
> set because kvm_arch_put_registers() erred out before it could call
> kvm_getput_regs(). This resulted in the guest crashing when OVMF tried to
> start the APs.
> 
> For a non-SEV-ES guest, I'm not sure if other updates could be missed,
> potentially.

Ok, thanks.  It's certainly a potential source of bugs, I've queued the 
patch.

Paolo