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

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Message-ID: <aLciEF5kNHDcRFvP@gcabiddu-mobl.ger.corp.intel.com>
Date: Tue, 2 Sep 2025 17:57:52 +0100
From: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
To: Jann Horn <jannh@...gle.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 02, 2025 at 06:31:49PM +0200, Jann Horn wrote:
> 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.)
Thanks. We will try to increase tlb_single_page_flush_ceiling before
4a02ed8e1cc3.

I'm not familiar with this code, but based on the commit message,
4a02ed8e1cc3 appears to be a refactor. However, that doesn't seem to be
the case.
Before the commit, mmu_notifier_arch_invalidate_secondary_tlbs() was
getting a modified value for start and end. After the commit it appears
to be using the original values instead. Was this intentional?

Regards,

-- 
Giovanni