From: "David Hildenbrand (Arm)" <david@kernel.org>
To: Zi Yan <ziy@nvidia.com>
Cc: Kaitao Cheng <kaitao.cheng@linux.dev>,
Andrew Morton <akpm@linux-foundation.org>,
Vlastimil Babka <vbabka@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>,
Brendan Jackman <jackmanb@google.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Liu Shixin <liushixin2@huawei.com>,
Oscar Salvador <osalvador@suse.de>,
muchun.song@linux.dev, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Kaitao Cheng <chengkaitao@kylinos.cn>
Subject: Re: [PATCH v2] mm: page_isolation: avoid unsafe folio reads while scanning compound pages
Date: Tue, 2 Jun 2026 21:37:25 +0200 [thread overview]
Message-ID: <48e3c0af-1c28-4a4f-a3f5-fa1f45f1c5ce@kernel.org> (raw)
In-Reply-To: <3BF8FD42-7792-4862-B5B3-79691618217D@nvidia.com>
On 6/2/26 21:31, Zi Yan wrote:
> On 2 Jun 2026, at 14:56, David Hildenbrand (Arm) wrote:
>
>> On 6/2/26 17:02, Zi Yan wrote:
>>>
>>>
>>> LGTM. Thanks.
>>>
>>> Just a comment, order can be dropped and use
>>> nr_pages = compound_nr(&folio->page) instead:
>>> 1. order > MAX_FOLIO_ORDER -> nr_pages > MAX_FOLIO_NR_PAGES
>>> 2. PAGE_SIZE << order -> PAGE_SIZE * nr_pages.
>>> But it is not worth a new version.
>>
>> If we use compound_nr, we have to check for power-of-2, like
>> scan_movable_pages(), as folio_large_nr_pages() might use the per-computed
>> value (which might read garbage).
>
> The power-of-2 requirement comes from “pfn | (nr_pages - 1)”, right?
Yes, you could end up stepping backwards, at least in the scan_movable_pages() case.
--
Cheers,
David
next prev parent reply other threads:[~2026-06-02 19:37 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-02 13:07 [PATCH v2] mm: page_isolation: avoid unsafe folio reads while scanning compound pages Kaitao Cheng
2026-06-02 15:02 ` Zi Yan
2026-06-02 17:11 ` Andrew Morton
2026-06-02 17:46 ` Zi Yan
2026-06-02 18:56 ` David Hildenbrand (Arm)
2026-06-02 19:31 ` Zi Yan
2026-06-02 19:37 ` David Hildenbrand (Arm) [this message]
2026-06-02 19:05 ` David Hildenbrand (Arm)
2026-06-03 5:35 ` Oscar Salvador (SUSE)
2026-06-11 7:52 ` Oscar Salvador (SUSE)
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