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? Thanks, Paolo
