linux-kernel - Re: [PATCH v4 3/8] x86/bugs: Use an X86_FEATURE_xxx flag for the MMIO Stale Data mitigation

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Message-ID: <20251112182435.od5oelwiitdueork@desk>
Date: Wed, 12 Nov 2025 10:24:35 -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 3/8] x86/bugs: Use an X86_FEATURE_xxx flag for the
 MMIO Stale Data mitigation

On Wed, Nov 12, 2025 at 03:46:55PM +0100, Borislav Petkov wrote:
> > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> > index 7129eb44adad..d1d7b5ec6425 100644
> > --- a/arch/x86/include/asm/cpufeatures.h
> > +++ b/arch/x86/include/asm/cpufeatures.h
> > @@ -501,6 +501,7 @@
> >  #define X86_FEATURE_ABMC		(21*32+15) /* Assignable Bandwidth Monitoring Counters */
> >  #define X86_FEATURE_MSR_IMM		(21*32+16) /* MSR immediate form instructions */
> >  #define X86_FEATURE_X2AVIC_EXT		(21*32+17) /* AMD SVM x2AVIC support for 4k vCPUs */
> > +#define X86_FEATURE_CLEAR_CPU_BUF_MMIO	(21*32+18) /* Clear CPU buffers using VERW before VMRUN, iff the vCPU can access host MMIO*/
> 							   ^^^^^^^
> 
> Yes, you can break the line and format it properly. :-)
> 
> Also, this should be called then
> 
> X86_FEATURE_CLEAR_CPU_BUF_VM_MMIO
> 
> as it is a VM-thing too.

+1. This is a VM-only flag.