Re: [kvm-unit-tests PATCH] x86: svm: low CR3 bits are not MBZ

[Krish Sadhukhan <krish.sadhukhan@oracle.com>]

On 8/17/20 11:38 PM, Paolo Bonzini wrote:
> On 05/08/20 01:13, Krish Sadhukhan wrote:
>> I did some experiments on the processor behavior on an Epyc 2 system via
>> KVM:
>>
>>    1. MBZ bits:  VMRUN passes even if these bits are set to 1 and
>> guest is exiting with exit code of            SVM_EXIT_VMMCALL.
>> According to the APM, this settting should constitute an invalid guest
>> state and hence I should get and exit code of SVM_EXIT_ERR. There's no
>> KVM check in place for these CR3 bits, so the check is all done in
>> hardware.
>>
>>    2. non-MBZ reserved bits:  Based on Nadav Amit's suggestion, I set
>> the 'not present' bit in an upper level NPT in order to trigger an NPF
>> and I did get an exit code of SVM_EXIT_NPF when I set any of these bits.
>> I am hoping that the processor has done the consistency check before it
>> tripped on NPF and not the other way around, so that our test is useful :
>>
>>     In PAE-legacy and non-PAE-legacy modes, the guest doesn't exit
>> with SVM_EXIT_VMMCALL when these bits are set to 0. I am not sure if I
>> am missing any special setting for the PAE-legacy and non-PAE-legacy
>> modes. In long-mode, however, the processor seems to behave as per APM,
>> i.e., guest exits with SVM_EXIT_VMMCALL when these bits are set to 0.
> Are you going to send patches for this?


Yes, I am working on it. I need to complete some more investigation.

>
> Thanks,
>
> Paolo
>