linux-kernel - Re: MMIO and VERW

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Message-ID: <20250318181515.42jf2p5onoueeg3v@desk>
Date: Tue, 18 Mar 2025 11:15:15 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: David Kaplan <david.kaplan@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H . Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
	Brendan Jackman <jackmanb@...gle.com>,
	Derek Manwaring <derekmn@...zon.com>
Subject: Re: MMIO and VERW

On Tue, Mar 18, 2025 at 06:37:08PM +0100, Borislav Petkov wrote:
> On Tue, Mar 18, 2025 at 09:56:45AM -0700, Pawan Gupta wrote:
> > On Tue, Mar 18, 2025 at 05:34:51PM +0100, Borislav Petkov wrote:
> > > On Tue, Mar 18, 2025 at 09:25:05AM -0700, Pawan Gupta wrote:
> > > > Rocket Lake, Comet Lake, Ice Lake with tsx=off only require VERW at
> > > > VMENTER. There are other MMIO affected CPUs that are not affected by MDS
> > > > and do not support TSX or disable it by default.
> > > 
> > > So all those CPUs are only affected by MMIO and not affected by neither of
> > > those:
> > > 
> > > TAA, RFDS, MDS
> > 
> > That is correct, they are not affected by MDS, TAA and RFDS.
> > 
> > > Or is that the case only when TSX is not enabled/not present there?
> > 
> > As per the affected CPU table [1], Ice Lake is not affected by TAA even if
> > TSX is enabled.
> 
> That table is insane - I need at least 4 monitors to stare at it properly. :-P

:D Totally agree. A machine readable format is here:
https://github.com/intel/Intel-affected-processor-list/blob/main/Intel_affected_processor_list.csv

> Anyway, so I'm wondering if we special-case those CPUs and have them select
> a special
> 
> MMIO_MITIGATION_VERW_VM
> 
> case and keep them separate from that whole
> CPUs-can-be-affected-by-multiple-vulns and the mitigation for all of them is
> VERW.
> 
> They will enable mmio_stale_data_clear and will be out of the equation.
> 
> Which will make this other logic simpler.

Likely yes, I will give this a shot and see how it compares with the
currrent implementation. Thanks for the suggestion.