linux-kernel - Re: Re: Re: Re: [PATCH] x86/bugs: KVM: Add support for SRSO_MSR

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Message-ID: <Z6_mY3a_FH-Zw4MC@google.com>
Date: Sat, 15 Feb 2025 00:57:07 +0000
From: Yosry Ahmed <yosry.ahmed@...ux.dev>
To: Borislav Petkov <bp@...en8.de>
Cc: Patrick Bellasi <derkling@...gle.com>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, x86@...nel.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Patrick Bellasi <derkling@...bug.net>,
	Brendan Jackman <jackmanb@...gle.com>
Subject: Re: Re: Re: Re: [PATCH] x86/bugs: KVM: Add support for SRSO_MSR_FIX

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