Re: Re: Re: Re: [PATCH] x86/bugs: KVM: Add support for SRSO_MSR_FIX

Yosry Ahmed
2025-02-15T00:57:25Z

On Fri, Feb 14, 2025 at 09:10:05PM +0100, Borislav Petkov wrote:
> On Thu, Feb 13, 2025 at 05:50:57PM +0000, Patrick Bellasi wrote:
> > The "should be set identically across all processors in the system" makes me
> > wondering if using the "KVM's user_return approach" proposed here is robust
> > enough. Could this not lead to the bit being possibly set only on some CPU
> > but not others?
>
> That's fine, we should update that paper.
>
> > If BpSpecReduce does not prevent training, but only the training from being
> > used, should not we keep it consistently set after a guest has run, or until an
> > IBPB is executed?
>
> After talking with folks internally, you're probably right. We should slap an
> IBPB before clearing. Which means, I cannot use the MSR return slots anymore.
> I will have to resurrect some of the other solutions we had lined up...
>
> Stay tuned.

Thanks for working on this!

Should this patch (and the two previously merged patches) be backported
to stable? I noticed they did not have CC:stable.

>
> Thx.
>
> --
> Regards/Gruss,
> Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette