linux-kernel - Re: [PATCH v13 06/14] x86/mm: use broadcast TLB flushing for page reclaim TLB flushing

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Message-ID: <297b28e9ef9f4cd983ae2e3dd4cf1fce8b74d0f1.camel@surriel.com>
Date: Wed, 26 Feb 2025 12:02:47 -0500
From: Rik van Riel <riel@...riel.com>
To: Tom Lendacky <thomas.lendacky@....com>, Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, peterz@...radead.org, 
	dave.hansen@...ux.intel.com, zhengqi.arch@...edance.com,
 nadav.amit@...il.com, 	kernel-team@...a.com, linux-mm@...ck.org,
 akpm@...ux-foundation.org, 	jackmanb@...gle.com, jannh@...gle.com,
 mhklinux@...look.com, 	andrew.cooper3@...rix.com, Manali.Shukla@....com,
 mingo@...nel.org
Subject: Re: [PATCH v13 06/14] x86/mm: use broadcast TLB flushing for page
 reclaim TLB flushing

On Wed, 2025-02-26 at 11:00 -0600, Tom Lendacky wrote:
> On 2/25/25 15:03, Borislav Petkov wrote:
> > On Tue, Feb 25, 2025 at 09:38:03PM +0100, Borislav Petkov wrote:
> > > On Tue, Feb 25, 2025 at 02:17:20PM -0500, Rik van Riel wrote:
> > > > Who do we need to ask to confirm that reading?
> > > 
> > > Lemme figure it out.
> > 
> > Confirmed - that really is the case.
> 
> Hmmm... since this is for host/hypervisor TLB handling, this makes me
> think that we should always be setting the ASID valid bit with 0 for
> the
> ASID value in EDX[15:0] on all INVLPGB instructions in this series.
> Otherwise we will also be flushing any guest ASID TLB entries that
> match
> the conditions, when that isn't intended.

The ASID is always zero in this series.

We only ever use the PCID for address space identification.

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