Re: [PATCH v3] mm/migrate: Fix do_pages_stat in 32-bit mode

[David Hildenbrand <david@redhat.com>]

On 01.07.25 19:55, Christoph Berg wrote:
> Re: Zi Yan
>> Fixes should be:
>>
>> Fixes: 5b1b561ba73c ("mm: simplify compat_sys_move_pages")
>>
>> Closes could be a link to the bug report.
> 
> Updated, thanks.
> 
>>> This seems to work, but honestly I am wondering, if copy_from_user
>>> needs a special 32-bit case, doesn't copy_to_user need special casing
>>> as well?
> 
> Scratch that, it works because an int[] is copied back, and that's
> always the same size.
> 
> So I think the patch is good to go.
> 
> Christoph
> 
> 

If you have to resend, next time resend the full patch separately, not 
as reply to the previous version.

>  From 426c93d558572248273cf386ca784626ae431413 Mon Sep 17 00:00:00 2001
> From: Christoph Berg <myon@debian.org>
> Date: Tue, 24 Jun 2025 16:44:27 +0200
> Subject: [PATCH v3] mm/migrate: Fix do_pages_stat in 32-bit mode

s/32-bit mode/compat mode/ ?

Because on native 32bit it should be working fine.

> 
> For arrays with more than 16 entries, the old code would incorrectly
> advance the pages pointer by 16 words instead of 16 compat_uptr_t.
> Fix by doing the pointer arithmetic inside get_compat_pages_array where
> pages32 is already a correctly-typed pointer.
> 
> Discovered while working on PostgreSQL 18's new NUMA introspection code.
> 
> Signed-off-by: Christoph Berg <myon@debian.org>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Fixes: 5b1b561ba73c ("mm: simplify compat_sys_move_pages")

Hmm, still not sure if 5b1b561ba73c really introduced the issue. I think 
it only messed with the "pages" pointer, not with the "status" pointer?

Hmmmm


I assume we want to Cc stable. @Andrew can do that.

> Reported-by: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
> Reported-by: Tomas Vondra <tomas@vondra.me>
> Closes: https://www.postgresql.org/message-id/flat/6342f601-77de-4ee0-8c2a-3deb50ceac5b%40vondra.me#86402e3d80c031788f5f55b42c459471
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb