Jim Mattson <jmattson@xxxxxxxxxx> writes: > On Fri, Feb 12, 2021 at 6:49 AM Bandan Das <bsd@xxxxxxxxxx> wrote: >> >> Paolo Bonzini <pbonzini@xxxxxxxxxx> writes: >> >> > On 11/02/21 22:22, Bandan Das wrote: >> >> The pcid-disabled test from kvm-unit-tests fails on a Milan host because the >> >> processor injects a #GP while the test expects #UD. While setting the intercept >> >> when the guest has it disabled seemed like the obvious thing to do, Babu Moger (AMD) >> >> pointed me to an earlier discussion here - https://lkml.org/lkml/2020/6/11/949 >> >> >> >> Jim points out there that #GP has precedence over the intercept bit when invpcid is >> >> called with CPL > 0 and so even if we intercept invpcid, the guest would end up with getting >> >> and "incorrect" exception. To inject the right exception, I created an entry for the instruction >> >> in the emulator to decode it successfully and then inject a UD instead of a GP when >> >> the guest has it disabled. >> >> >> >> Bandan Das (3): >> >> KVM: Add a stub for invpcid in the emulator table >> >> KVM: SVM: Handle invpcid during gp interception >> >> KVM: SVM: check if we need to track GP intercept for invpcid >> >> >> >> arch/x86/kvm/emulate.c | 3 ++- >> >> arch/x86/kvm/svm/svm.c | 22 +++++++++++++++++++++- >> >> 2 files changed, 23 insertions(+), 2 deletions(-) >> >> >> > >> > Isn't this the same thing that "[PATCH 1/3] KVM: SVM: Intercept >> > INVPCID when it's disabled to inject #UD" also does? >> > >> Yeah, Babu pointed me to Sean's series after I posted mine. >> 1/3 indeed will fix the kvm-unit-test failure. IIUC, It doesn't look like it >> handles the case for the guest executing invpcid at CPL > 0 when it's >> disabled for the guest - #GP takes precedence over intercepts and will >> be incorrectly injected instead of an #UD. > > I know I was the one to complain about the #GP, but... > > As a general rule, kvm cannot always guarantee a #UD for an > instruction that is hidden from the guest. Consider, for example, > popcnt, aesenc, vzeroall, movbe, addcx, clwb, ... > I'm pretty sure that Paolo has brought this up in the past when I've > made similar complaints. Ofcourse, even for vm instructions failures, the fixup table always jumps to a ud2. I was just trying to address the concern because it is possible to inject the correct exception via decoding the instruction. Bandan
