lkml.org 
[lkml]   [2020]   [Jun]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH] Fix undefined operation VMXOFF during reboot and crash
On Wed, Jun 10, 2020 at 5:00 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> On Wed, Jun 10, 2020 at 02:59:19PM -0700, Andy Lutomirski wrote:
> >
> >
> > > On Jun 10, 2020, at 11:21 AM, David P. Reed <dpreed@deepplum.com> wrote:
> > >
> > > If a panic/reboot occurs when CR4 has VMX enabled, a VMXOFF is
> > > done on all CPUS, to allow the INIT IPI to function, since
> > > INIT is suppressed when CPUs are in VMX root operation.
> > > However, VMXOFF causes an undefined operation fault if the CPU is not
> > > in VMX operation, that is, VMXON has not been executed, or VMXOFF
> > > has been executed, but VMX is enabled.
> >
> > I’m surprised. Wouldn’t this mean that emergency reboots always fail it a VM
> > is running? I would think someone would have noticed before.
>
> The call to cpu_vmxoff() is conditioned on CR4.VMXE==1, which KVM toggles in
> tandem with VMXON and VMXOFF. Out of tree hypervisors presumably do the
> same. That's obviously not atomic though, e.g. VMXOFF will #UD if the
> vmxoff_nmi() NMI arrives between CR4.VMXE=1 and VMXON, or between VMXOFF
> and CR4.VMXE=0.

It would be nice for the commit message to say "this happens when
nmxoff_nmi() races with KVM's VMXON/VMXOFF toggling". Or the commit
message should say something else if the bug happens for a different
reason.

The race with KVM should be quite unusual, since it involves rebooting
concurrently with loading or unloading KVM.

\
 
 \ /
  Last update: 2020-06-11 02:16    [W:0.067 / U:2.220 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site