On Tue, Jun 2, 2020 at 7:24 PM Sean Christopherson
<sean.j.christopherson@xxxxxxxxx> wrote:
>
> On Tue, Jun 02, 2020 at 10:33:51AM -0700, Jim Mattson wrote:
> > On Mon, Jun 1, 2020 at 6:21 PM Sean Christopherson
> > <sean.j.christopherson@xxxxxxxxx> wrote:
> > >
> > > On Mon, Jun 01, 2020 at 03:24:15PM -0700, Jim Mattson wrote:
> > > > As we already do in svm, record the last logical processor on which a
> > > > vCPU has run, so that it can be communicated to userspace for
> > > > potential hardware errors.
> > > >
> > > > Signed-off-by: Jim Mattson <jmattson@xxxxxxxxxx>
> > > > Reviewed-by: Oliver Upton <oupton@xxxxxxxxxx>
> > > > Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
> > > > ---
> > > > arch/x86/kvm/vmx/vmx.c | 1 +
> > > > arch/x86/kvm/vmx/vmx.h | 3 +++
> > > > 2 files changed, 4 insertions(+)
> > > >
> > > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > > > index 170cc76a581f..42856970d3b8 100644
> > > > --- a/arch/x86/kvm/vmx/vmx.c
> > > > +++ b/arch/x86/kvm/vmx/vmx.c
> > > > @@ -6730,6 +6730,7 @@ static fastpath_t vmx_vcpu_run(struct kvm_vcpu *vcpu)
> > > > if (vcpu->arch.cr2 != read_cr2())
> > > > write_cr2(vcpu->arch.cr2);
> > > >
> > > > + vmx->last_cpu = vcpu->cpu;
> > >
> > > This is redundant in the EXIT_FASTPATH_REENTER_GUEST case. Setting it
> > > before reenter_guest is technically wrong if emulation_required is true, but
> > > that doesn't seem like it'd be an issue in practice.
> >
> > I really would like to capture the last logical processor to execute
> > VMLAUNCH/VMRESUME (or VMRUN on the AMD side) on behalf of this vCPU.
>
> Does it matter though? The flows that consume the variable are all directly
> in the VM-Exit path.
>
> > > > vmx->fail = __vmx_vcpu_run(vmx, (unsigned long *)&vcpu->arch.regs,
> > > > vmx->loaded_vmcs->launched);
> > > >
> > > > diff --git a/arch/x86/kvm/vmx/vmx.h b/arch/x86/kvm/vmx/vmx.h
> > > > index 672c28f17e49..8a1e833cf4fb 100644
> > > > --- a/arch/x86/kvm/vmx/vmx.h
> > > > +++ b/arch/x86/kvm/vmx/vmx.h
> > > > @@ -302,6 +302,9 @@ struct vcpu_vmx {
> > > > u64 ept_pointer;
> > > >
> > > > struct pt_desc pt_desc;
> > > > +
> > > > + /* which host CPU was used for running this vcpu */
> > > > + unsigned int last_cpu;
> > >
> > > Why not put this in struct kvm_vcpu_arch? I'd also vote to name it
> > > last_run_cpu, as last_cpu is super misleading.
> >
> > I think last_run_cpu may also be misleading, since in the cases of
> > interest, nothing actually 'ran.' Maybe last_attempted_vmentry_cpu?
>
> Ya, that thought crossed my mind as well.
>
> > > And if it's in arch, what about setting it vcpu_enter_guest?
> >
> > As you point out above, this isn't entirely accurate. (But that's the
> > way we roll in kvm, isn't it? :-)
>
> As an alternative to storing the last run/attempted CPU, what about moving
> the "bad VM-Exit" detection into handle_exit_irqoff, or maybe a new hook
> that is called after IRQs are enabled but before preemption is enabled, e.g.
> detect_bad_exit or something? All of the paths in patch 4/4 can easily be
> moved out of handle_exit. VMX would require a little bit of refacotring for
> it's "no handler" check, but that should be minor.
Given the alternatives, I'm willing to compromise my principles wrt
emulation_required. :-) I'll send out v4 soon.
