linux-kernel - Re: [PATCH v2 4/6] x86/bugs: Use a static branch to guard IBPB on vCPU switch

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Message-ID: <Z7_C8a9oGp8lskhh@google.com>
Date: Wed, 26 Feb 2025 17:42:09 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Yosry Ahmed <yosry.ahmed@...ux.dev>
Cc: x86@...nel.org, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
	"H. Peter Anvin" <hpa@...or.com>, Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, 
	Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Josh Poimboeuf <jpoimboe@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, 
	Jim Mattson <jmattson@...gle.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] x86/bugs: Use a static branch to guard IBPB on
 vCPU switch

On Thu, Feb 27, 2025, Yosry Ahmed wrote:
> Instead of using X86_FEATURE_USE_IBPB to guard the IBPB execution in KVM
> when a new vCPU is loaded, introduce a static branch, similar to
> switch_mm_*_ibpb.
> 
> This makes it obvious in spectre_v2_user_select_mitigation() what
> exactly is being toggled, instead of the unclear X86_FEATURE_USE_IBPB
> (which will be shortly removed). It also provides more fine-grained
> control, making it simpler to change/add paths that control the IBPB in
> the vCPU switch path without affecting other IBPBs.
> 
> Signed-off-by: Yosry Ahmed <yosry.ahmed@...ux.dev>
> Acked-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---

Acked-by: Sean Christopherson <seanjc@...gle.com>