linux-kernel - Re: [PATCH v4 1/8] x86/bugs: Use VM_CLEAR_CPU

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Message-ID: <20251112181905.nvdurg5zsogixp4z@desk>
Date: Wed, 12 Nov 2025 10:19:05 -0800
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Brendan Jackman <jackmanb@...gle.com>
Subject: Re: [PATCH v4 1/8] x86/bugs: Use VM_CLEAR_CPU_BUFFERS in VMX as well

On Wed, Nov 12, 2025 at 11:23:36AM +0100, Borislav Petkov wrote:
> On Tue, Nov 11, 2025 at 02:03:40PM -0800, Sean Christopherson wrote:
> > How about:
> > 
> > /* If necessary, emit VERW on exit-to-userspace to clear CPU buffers. */
> > #define CLEAR_CPU_BUFFERS \
> > 	ALTERNATIVE "", __CLEAR_CPU_BUFFERS, X86_FEATURE_CLEAR_CPU_BUF
> 
> By the "If necessary" you mean whether X86_FEATURE_CLEAR_CPU_BUF is set or
> not, I presume...
> 
> I was just wondering whether this macro is going to be used somewhere else
> *except* on the kernel->user vector.

I believe the intent is to use it only at kernel->user transition.