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Thu, 11 Dec 2025 05:38:05 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id fuLNC71YOmkmLwAAD6G6ig (envelope-from ); Thu, 11 Dec 2025 05:38:05 +0000 Date: Thu, 11 Dec 2025 06:38:03 +0100 From: Oscar Salvador To: "David Hildenbrand (Red Hat)" Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, linux-mm@kvack.org, Will Deacon , "Aneesh Kumar K.V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Arnd Bergmann , Muchun Song , "Liam R. Howlett" , Lorenzo Stoakes , Vlastimil Babka , Jann Horn , Pedro Falcato , Rik van Riel , Harry Yoo , Laurence Oberman , Prakash Sangappa , Nadav Amit , stable@vger.kernel.org, Liu Shixin Subject: Re: [PATCH v1 1/4] mm/hugetlb: fix hugetlb_pmd_shared() Message-ID: References: <20251205213558.2980480-1-david@kernel.org> <20251205213558.2980480-2-david@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20251205213558.2980480-2-david@kernel.org> X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 5D8D240006 X-Stat-Signature: 55jhcxxuifh1obca1joz7rpd4fem31am X-Rspam-User: X-HE-Tag: 1765431489-34557 X-HE-Meta: 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 0dqkKvZ6 GybbkCbkbPK36k0rLDSvN8hdpDNqRGIYUnEk/kAALXveub2SKKVBdryEmGJ14h/jZkliVrHutzaJu9m/MbVVh25+fsG0ASiIvVnk78y1f+iaqQLyev3EDBO1Pne2YdKmp6dwUuFSidCx3W4obvjxR9k2BQGR6hu2bPFH8rItIbZvf/NgcG9dCIVZesLSq/4MmFnJwHeBBWhaPaQsONHDuv6sFaUDZ2Nty4tMIzC671L3nHRJKxvzZ3yOCg77BHK2htTqsBNQKFyaK5C84cGXEJtbtk3FY9XRYkgsVNiT+x8JAt9/wx7WN18uB/kN3fG24j+wGmyQsDTLjBc0xvo3TUakQqsCuIaXx/0ZQlsM+5/23DWQHiOXczyUjJ3VDaAzPZJXPbHWlqUs3UQ+EsgGPLWpmAW/yjKB6sdLsCZCYnnLeAebGDxGVDwK/1g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Dec 05, 2025 at 10:35:55PM +0100, David Hildenbrand (Red Hat) wrote: > We switched from (wrongly) using the page count to an independent > shared count. Now, shared page tables have a refcount of 1 (excluding > speculative references) and instead use ptdesc->pt_share_count to > identify sharing. > > We didn't convert hugetlb_pmd_shared(), so right now, we would never > detect a shared PMD table as such, because sharing/unsharing no longer > touches the refcount of a PMD table. > > Page migration, like mbind() or migrate_pages() would allow for migrating > folios mapped into such shared PMD tables, even though the folios are > not exclusive. In smaps we would account them as "private" although they > are "shared", and we would be wrongly setting the PM_MMAP_EXCLUSIVE in the > pagemap interface. > > Fix it by properly using ptdesc_pmd_is_shared() in hugetlb_pmd_shared(). > > Fixes: 59d9094df3d7 ("mm: hugetlb: independent PMD page table shared count") > Cc: > Cc: Liu Shixin > Signed-off-by: David Hildenbrand (Red Hat) Good catch David, Acked-by: Oscar Salvador > --- > include/linux/hugetlb.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h > index 019a1c5281e4e..03c8725efa289 100644 > --- a/include/linux/hugetlb.h > +++ b/include/linux/hugetlb.h > @@ -1326,7 +1326,7 @@ static inline __init void hugetlb_cma_reserve(int order) > #ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING > static inline bool hugetlb_pmd_shared(pte_t *pte) > { > - return page_count(virt_to_page(pte)) > 1; > + return ptdesc_pmd_is_shared(virt_to_ptdesc(pte)); > } > #else > static inline bool hugetlb_pmd_shared(pte_t *pte) > -- > 2.52.0 > > -- Oscar Salvador SUSE Labs