linux-kernel - Re: [BUG] x86/mm: regression after 4a02ed8e1cc3

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Message-ID: <CAG48ez2ck2QaxZ6G1Qrp9p0brFecrnf+KRc7Uk8c9kMJqSOswg@mail.gmail.com>
Date: Tue, 2 Sep 2025 18:31:49 +0200
From: Jann Horn <jannh@...gle.com>
To: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
Cc: Rik van Riel <riel@...riel.com>, x86@...nel.org, linux-kernel@...r.kernel.org, 
	bp@...en8.de, peterz@...radead.org, dave.hansen@...ux.intel.com, 
	zhengqi.arch@...edance.com, nadav.amit@...il.com, thomas.lendacky@....com, 
	kernel-team@...a.com, linux-mm@...ck.org, akpm@...ux-foundation.org, 
	jackmanb@...gle.com, mhklinux@...look.com, andrew.cooper3@...rix.com, 
	Manali.Shukla@....com, mingo@...nel.org, Dave Hansen <dave.hansen@...el.com>, 
	baolu.lu@...el.com, david.guckian@...el.com, damian.muszynski@...el.com
Subject: Re: [BUG] x86/mm: regression after 4a02ed8e1cc3

On Tue, Sep 2, 2025 at 5:44 PM Giovanni Cabiddu
<giovanni.cabiddu@...el.com> wrote:
> On Tue, Feb 25, 2025 at 10:00:36PM -0500, Rik van Riel wrote:
> > Reduce code duplication by consolidating the decision point
> > for whether to do individual invalidations or a full flush
> > inside get_flush_tlb_info.
> >
> > Signed-off-by: Rik van Riel <riel@...riel.com>
> > Suggested-by: Dave Hansen <dave.hansen@...el.com>
> > Tested-by: Michael Kelley <mhklinux@...look.com>
> > Acked-by: Dave Hansen <dave.hansen@...el.com>
> > Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>
> > ---
> After 4a02ed8e1cc3 ("x86/mm: Consolidate full flush threshold
> decision"), we've seen data corruption in DMAd buffers when testing SVA.

If it's not too much effort, you could try to see whether bumping
/sys/kernel/debug/x86/tlb_single_page_flush_ceiling to some relatively
large value (maybe something like 262144, which is 512*512) causes you
to see the same kind of issue before commit 4a02ed8e1cc3. (Note that
increasing tlb_single_page_flush_ceiling costs performance, and
putting an overly big value in there will probably make the system
completely unresponsive.)