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
