linux-kernel - Re: [PATCH v2 3/4] x86/bugs: KVM: Add support for SRSO_MSR

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Message-ID: <20250108194520.GIZ37V0OVGLtRAWSF_@fat_crate.local>
Date: Wed, 8 Jan 2025 20:45:20 +0100
From: Borislav Petkov <bp@...en8.de>
To: Jim Mattson <jmattson@...gle.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Borislav Petkov <bp@...nel.org>, X86 ML <x86@...nel.org>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Josh Poimboeuf <jpoimboe@...hat.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	KVM <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] x86/bugs: KVM: Add support for SRSO_MSR_FIX

On Wed, Jan 08, 2025 at 11:43:14AM -0800, Jim Mattson wrote:
> > We don't need safe-RET with SRSO_USER_KERNEL_NO=1. And there's no safe-RET for
> > virt only. So IBPB-on-VMEXIT is the next best thing. The good thing is, those
> > machines have BpSpecReduce too so you won't be doing IBPB-on-VMEXIT either but
> > what we're talking about here - BpSpecReduce.
> 
> I'm suggesting that IBPB-on-VMexit is probably the *worst* thing.

I know what you're suggesting and I don't think so but I'd need to look at the
numbers.

> If it weren't for BpSpecReduce, I would want safe-RET for virt only.

Read my reply again.

> (Well, if it weren't for ASI, I would want that, anyway.)

I'm sure Brendan is waiting for reviews there.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette