On Mon, May 17, 2021, Paolo Bonzini wrote: > On 14/05/21 07:11, Andy Lutomirski wrote: > > I don't even want to think about what happens if a perf NMI hits and > > accesses host user memory while the guest PKRU is live (on VMX -- I > > think this can't happen on SVM). > > This is indeed a problem, which indeed cannot happen on SVM but is there on > VMX. Note that the function above is not handling all of the xstate, it's > handling the *XSAVE state*, that is XCR0, XSS and PKRU. Thus the window is > small, but it's there. > > Is it solvable at all, without having PKRU fields in the VMCS (and without > masking NMIs in the LAPIC which would be too expensive)? Dave, Sean, what > do you think? The least awful solution would be to have the NMI handler restore the host's PKRU. The NMI handler would need to save/restore the register, a la CR2, but the whole thing could be optimized to run if and only if the NMI lands in the window where the guest's PKRU is loaded.
