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

Borislav Petkov
2025-02-14T20:10:28Z

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.

Thx.

--
Regards/Gruss,
Boris.