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[70.49.81.60]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8ffd7c1fd2bsm175197236d6.27.2026.07.14.10.41.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 14 Jul 2026 10:41:16 -0700 (PDT) Message-ID: <690257d2-2126-4a8e-86de-b0882e282431@redhat.com> Date: Tue, 14 Jul 2026 13:41:16 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/util: don't read __page_2 for order-1 folios in snapshot_page() To: Aboorva Devarajan , Andrew Morton , David Hildenbrand Cc: Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Sourabh Jain , Ritesh Harjani , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org References: <20260708201954.686111-1-aboorvad@linux.ibm.com> Content-Language: en-US, en-CA From: Luiz Capitulino In-Reply-To: <20260708201954.686111-1-aboorvad@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2026-07-08 16:19, Aboorva Devarajan wrote: > snapshot_page() currently reads __page_2 after checking nr_pages > 1, > but it should only do so when nr_pages > 2. > > During DLPAR memory remove on a 22 TB ppc64le LPAR, snapshot_page() > oopsed on the page isolation path while reading an order-1 folio's > __page_2 from an adjacent absent section (unmapped vmemmap). > > Fix this to avoid reading memmap that doesn't exist (e.g., a vmemmap > hole). Reviewed-by: Luiz Capitulino > > Fixes: 31a31da8a618 ("mm: move _pincount in folio to page[2] on 32bit") > Cc: stable@vger.kernel.org # v6.15+ > Reported-by: Sourabh Jain > Acked-by: David Hildenbrand (Arm) > Reviewed-by: Lorenzo Stoakes > Signed-off-by: Aboorva Devarajan > --- > v1 -> v2: > - Condense the commit message. > - Drop the code comment. > > mm/util.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/util.c b/mm/util.c > index af2c2103f0d95..34cb43b3eaa4c 100644 > --- a/mm/util.c > +++ b/mm/util.c > @@ -1353,7 +1353,7 @@ void snapshot_page(struct page_snapshot *ps, const struct page *page) > if (ps->idx < MAX_FOLIO_NR_PAGES) { > memcpy(&ps->folio_snapshot, foliop, 2 * sizeof(struct page)); > nr_pages = folio_nr_pages(&ps->folio_snapshot); > - if (nr_pages > 1) > + if (nr_pages > 2) > memcpy(&ps->folio_snapshot.__page_2, &foliop->__page_2, > sizeof(struct page)); > set_ps_flags(ps, foliop, page);