linux-kernel - Re: [PATCH v2] mm: madvise: use walk_page_range_vma() instead of walk_page

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Message-ID: <4f1edbf8-eb6a-4081-8b49-c9d1a5f85748@lucifer.local>
Date: Mon, 9 Jun 2025 12:12:17 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Barry Song <21cnbao@...il.com>
Cc: akpm@...ux-foundation.org, Liam.Howlett@...cle.com,
        anshuman.khandual@....com, david@...hat.com, dev.jain@....com,
        jannh@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        lokeshgidra@...gle.com, osalvador@...e.de, ryan.roberts@....com,
        surenb@...gle.com, v-songbaohua@...o.com, vbabka@...e.cz,
        zhengtangquan@...o.com
Subject: Re: [PATCH v2] mm: madvise: use walk_page_range_vma() instead of
 walk_page_range()

On Mon, Jun 09, 2025 at 10:55:13PM +1200, Barry Song wrote:
> > Yeah dear god I missed this oops!
> >
> > Yeah Barry - could you revert this change for the guard region bits please? So
> > this is intentional as we do not want anything non-mm to have access to
> > install_pte.
>
> All my fault! I wrote a multi-process/thread test to issue lots of madvise
> calls, but it looks like I missed INSTALL_GUARD.
>
> Thanks, Ryan & Lorenzo! Does Andrew prefer to pick up the fix below, or
> would it be better to send a new version? He’s handled fixes like this in
> the past—happy to resend if needed.

I'm totally fine with this thanks!

I can't speak for Andrew of course but he highlighted at LSF/MM his
preference for incremental fixes like this so I would say this is probably
his preference also :)

>
> From: Barry Song <v-songbaohua@...o.com>
> Date: Mon, 9 Jun 2025 22:42:13 +1200
> Subject: [PATCH] mm: madvise: revert the walk_page_range_vma change for
>  MADV_GUARD_INSTALL
>
> Fix the broken MADV_GUARD_INSTALL reported by Ryan.
>  # guard-regions.c:719:split_merge:Expected madvise(ptr, 10 * page_size,
>  MADV_GUARD_INSTALL) (-1) == 0 (0)
>
> Reported-by: Ryan Roberts <ryan.roberts@....com>
> Closes: https://lore.kernel.org/linux-mm/671f8164-a90b-48d7-9446-359eb9493500@arm.com/
> Signed-off-by: Barry Song <v-songbaohua@...o.com>
> ---
>  mm/madvise.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/madvise.c b/mm/madvise.c
> index 8382614b71d1..381eedde8f6d 100644
> --- a/mm/madvise.c
> +++ b/mm/madvise.c
> @@ -1141,7 +1141,7 @@ static long madvise_guard_install(struct vm_area_struct *vma,
>  		unsigned long nr_pages = 0;
>
>  		/* Returns < 0 on error, == 0 if success, > 0 if zap needed. */
> -		err = walk_page_range_vma(vma, start, end,
> +		err = walk_page_range_mm(vma->vm_mm, start, end,
>  					 &guard_install_walk_ops, &nr_pages);

Actually ack that only the install needs it, we can keep this fix for the
remove, as that doesn't of course use .install_pte().

Also it's kind of neat to only use the internal one in the instance we need
that and the 'public' interface when we don't.

>  		if (err < 0)
>  			return err;
> --
> 2.39.3 (Apple Git-146)
>

I also did actually test this this time :P and can confirm it fixes the issue.