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.
