linux-kernel - Re: [PATCH] mm/huge_memory: fix override of entry in remove_migration

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Message-ID: <240b0a40-c0da-4995-b7a8-cc98797dd0a2@kernel.org>
Date: Fri, 14 Nov 2025 10:25:32 +0100
From: "David Hildenbrand (Red Hat)" <david@...nel.org>
To: Balbir Singh <balbirs@...dia.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, dri-devel@...ts.freedesktop.org
Cc: Andrew Morton <akpm@...ux-foundation.org>, Zi Yan <ziy@...dia.com>,
 Joshua Hahn <joshua.hahnjy@...il.com>, Rakie Kim <rakie.kim@...com>,
 Byungchul Park <byungchul@...com>, Gregory Price <gourry@...rry.net>,
 Ying Huang <ying.huang@...ux.alibaba.com>,
 Alistair Popple <apopple@...dia.com>, Oscar Salvador <osalvador@...e.de>,
 Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lyude Paul <lyude@...hat.com>,
 Danilo Krummrich <dakr@...nel.org>, David Airlie <airlied@...il.com>,
 Simona Vetter <simona@...ll.ch>, Ralph Campbell <rcampbell@...dia.com>,
 Mika Penttilä <mpenttil@...hat.com>,
 Matthew Brost <matthew.brost@...el.com>,
 Francois Dugast <francois.dugast@...el.com>
Subject: Re: [PATCH] mm/huge_memory: fix override of entry in
 remove_migration_pmd

On 14.11.25 02:24, Balbir Singh wrote:
> On 11/14/25 12:21, Balbir Singh wrote:
>> Recent changes exposed a BUG in remove_migration_pmd() where the
>> migration entry was being overridden when the folio is device private.
>>
>> Use scope local entry for creating the device private pmde. Make the
>> pmde writable if the migration entry is writable by moving the check
>> is_migration_write() prior to creating the device private entry.
>>
>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>> Cc: David Hildenbrand <david@...hat.com>
>> Cc: Zi Yan <ziy@...dia.com>
>> Cc: Joshua Hahn <joshua.hahnjy@...il.com>
>> Cc: Rakie Kim <rakie.kim@...com>
>> Cc: Byungchul Park <byungchul@...com>
>> Cc: Gregory Price <gourry@...rry.net>
>> Cc: Ying Huang <ying.huang@...ux.alibaba.com>
>> Cc: Alistair Popple <apopple@...dia.com>
>> Cc: Oscar Salvador <osalvador@...e.de>
>> Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>> Cc: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
>> Cc: Nico Pache <npache@...hat.com>
>> Cc: Ryan Roberts <ryan.roberts@....com>
>> Cc: Dev Jain <dev.jain@....com>
>> Cc: Barry Song <baohua@...nel.org>
>> Cc: Lyude Paul <lyude@...hat.com>
>> Cc: Danilo Krummrich <dakr@...nel.org>
>> Cc: David Airlie <airlied@...il.com>
>> Cc: Simona Vetter <simona@...ll.ch>
>> Cc: Ralph Campbell <rcampbell@...dia.com>
>> Cc: Mika Penttilä <mpenttil@...hat.com>
>> Cc: Matthew Brost <matthew.brost@...el.com>
>> Cc: Francois Dugast <francois.dugast@...el.com>
>>
>> Signed-off-by: Balbir Singh <balbirs@...dia.com>
>> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>> ---
>>   mm/huge_memory.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
> 
> Hi, Andrew
> 
> This patch fixes a bug in mm/rmap: extend rmap and migration support device-private entries
> in the thp device-private series.

When you resend, best to add under the "--" something like

"This fixup should be squashed into the patch "$NAMEOFCOMMIT" in 
mm/mm-unstable"

It is also helpful to call the patch then

"fixup: $NAMEOFCOMMIT"

So it's immediately clear that this is something to be squashed.

-- 
Cheers

David