Re: [PATCH] KVM: x86: fix a typo in __try_cmpxchg_user that caused cmpxchg to be not atomic

Maxim Levitsky
2022-05-16T13:14:45Z

On Thu, 2022-05-12 at 21:27 +0000, Sean Christopherson wrote:
> On Thu, May 12, 2022, Paolo Bonzini wrote:
> > On 5/12/22 12:14, Maxim Levitsky wrote:
> > > Yes, this is the root cause of the TDP mmu leak I was doing debug of in the last week.
> > > Non working cmpxchg on which TDP mmu relies makes it install two differnt shadow pages
> > > under same spte.
> >
> > Awesome! And queued, thanks.
>
> If you haven't done so already, can you add
>
> Cc: stable@vger.kernel.org

When I posted my patch, I checked that the patch didn't reach mainline yet,
so I assumed that it won't be in -stable either yet, although it was CCed there.

>
> Also, given that we have concrete proof that not honoring atomic accesses can have
> dire consequences for the guest, what about adding a capability to turn the emul_write
> path into an emulation error?
>

This is a good idea. It might though break some guests - I did see that
warning few times, that is why I wasn't alert by the fact that it started showing up more often.

I'll take a look at this soon.

Best regards,
Maxim Levitsky