Re: [RFC PATCH] KVM: x86: Protect the unused bits in MSR exiting flags

[Sean Christopherson <seanjc@google.com>]

On Tue, Jul 19, 2022, Paolo Bonzini wrote:
> On 7/14/22 18:13, Aaron Lewis wrote:
> > ---
> > 
> > Posting as an RFC to get feedback whether it's too late to protect the
> > unused flag bits.  My hope is this feature is still new enough, and not
> > widely used enough, and this change is reasonable enough to be able to be
> > corrected.  These bits should have been protected from the start, but
> > unfortunately they were not.
> > 
> > Another option would be to correct this by adding a quirk, but fixing
> > it that has its down sides.   It complicates the code more than it
> > would otherwise be, and complicates the usage for anyone using any new
> > features introduce in the future because they would also have to enable
> > a quirk.  For long term simplicity my hope is to be able to just patch
> > the original change.
> 
> Yes, let's do it this way.

Heh, which way is "this way"?

  (a) Fix KVM_CAP_X86_USER_SPACE_MSR and cross our fingers
  (b) Add a quirk
  (c) ???