From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793306290; b=QmbFBfzZxWLyvBpcZ1w5NchDdBNJ74JS4paAVL96BqXXLNeL96b66AENq1U8Z49C5r7Z VK0kbBnn/mF+gDAJFBotpiMWUq1xFeH/9iMzimQXwh0DTtB9uTUk8nO9kOr+Z0EwuVmqp ldqE2gwSvx8gnGuG7cJFdsxUfCNcBr8R42xFUeuP01jcV91gyKbCflqC1VyyZUGTjqZrP wWD6mSClKiIQ2LPqrvFrQBMNBb/gNyKbEqB8j6zblMDHxv1XIi585maRZUUovFM5LFlLq DOILE7ujDkWkTyYq0ULpsM4mKRT4t3QRPLcwkdjCgpMFPN22ySkctfNrHp8y4wbXeBQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793306290; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=nj1Bf9db8TNcajGSKnb6DbuHi/phVwkCDM1cIZai6DI=; b=WCGSXcfCsxbqKgTVxlWqu5wxDTm9fTbyEi9k/kGqsV35cDy9BcyrRZCuUejQFY4CZUV2 61PpU3ykQd2+LYhkXAntYrgi9m+LVBi8MlJdP8hX9L7VB+pjhI6nJ1U1jEkjViI0ifAsj hsjscLyvlN+QoR0vS+ZAS+eGtSBFcVtbtv8AHuXZLqKfN2VD6hzg12f7z0do9MEdiNDtJ gFsf2BnhRlQIFe90GpBcl1yjzxTDQhKLLz1NWiVmBfpKqiBkonMLNwOgCBGkIKV77GJiv z3lzIOB/MRhBC//9N/B2hOZmGE/AMdFD8Iuqa1g9Jtby6BqwIhzDVs1HC1KfcseFJiQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FIuxTTI3; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 90ADA606A31C; Thu, 29 Oct 2026 20:38:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FIuxTTI3 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1BE841F01825; Thu, 29 Oct 2026 20:37:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306290; bh=nj1Bf9db8TNcajGSKnb6DbuHi/phVwkCDM1cIZai6DI=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=FIuxTTI3C9PGyWVFGo4s1b0dkDlzRfab9Rj6I74MTLycqi+2Em6LiHU/uAvrS9N2K H1lysuB2CyMvu8AUoaV21WSVGPL5xMuFv701vHfyNuvbTOqOVl1Mb27qjgobqyD4Ih w521JBB1DU2+1WGBmfWNyNI9L0QxayWIoR/35/8S6lbTgqbOOCRUYTrMQVyzhih2Uy 5YOZ+Uv9eZAqw/sFSkR0LDJjCsJd17NT85n8UbO6chx+PkSu1BaBgYlPYiLxlSRP0s YNrqZmF/rZnmJY1dOZd/zKWR/IT1NfuAz2jIJEzyiNNCuLG/4f2hBHEDIvx0IURMf/ 8vhdjMEwBOimg== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:14 +0100 Subject: [PATCH v2 19/47] mm/gup: recheck the PUD under PTL in follow_pud_mask() X-Mailing-List: linux-arch@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261029-fixes_core-v2-19-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, stable@vger.kernel.org, Josef Bacik , "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=3795; i=david@kernel.org; h=from:subject:message-id; bh=PWJnBAFtWkzROraFyD6718GFghC4dRBvxtyaTiDuAbI=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer23rib/wxOTO+QCt1Qe9WZRKlh48bPQzJd5VePoC4 U+SnnmGHaUsDGIcDLJiiixBwfcNXr5cV1vtxscMM4eVCWQIAxenAEzEjI2RYcKTwxteKM7pfsr5 l+9Y52+mDR9eFry6cu7nmmdGkT3yTnmMDE90/nzPfmm/TfZaV3vaLZ02o7usjFJSH3c4GdrG75m 0hBUA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A follow_pud_mask() reads the PUD without a lock. If it is a leaf, it takes the lock and calls follow_huge_pud(), which reads the entry again, but only tests whether it is present. A leaf can be zapped concurrently and a page fault can fill the empty entry with a page table. This currently only applies when device-dax makes use of PUD entries, and the fault after e.g., MADV_DONTNEED would find THPs to be disabled. That requires a sequence like 1) Fault in the PUD 2) Disable THP 3) Have GUP race against concurrent MADV_DONTNEED + refault Which is rather unlikely to happen in practice, which is why we never received a report about such a problem. Before commit 1b1676180246 ("mm/gup: handle huge pud for follow_pud_mask()"), we performed that check in follow_devmap_pud() by testing for pud_devmap(). Let's fix it by just structuring follow_pud_mask() similar to follow_pmd_mask(), minus protnone stuff that does not apply and minus FOLL_SPLIT_PMD handling. That makes it much easier to spot any such inconsistencies. Perform the pud_bad() check early in follow_pmd_mask() and just forward the PUD value. We can drop the pud_present() check in follow_huge_pud(), just like we have in follow_huge_pmd(). Even though we are performing more changes than strictly necessary, the fix should be easy to backport. Fixes: 1b1676180246 ("mm/gup: handle huge pud for follow_pud_mask()") Cc: stable@vger.kernel.org Reported-by: Josef Bacik Signed-off-by: David Hildenbrand (Arm) --- mm/gup.c | 32 ++++++++++++++++++-------------- 1 file changed, 18 insertions(+), 14 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 7d43ce717b24..f809361227e7 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -658,9 +658,6 @@ static struct page *follow_huge_pud(struct vm_area_struct *vma, assert_spin_locked(pud_lockptr(mm, pudp)); - if (!pud_present(pud)) - return NULL; - if ((flags & FOLL_WRITE) && !can_follow_write_pud(pud, pfn_to_page(pfn), vma, flags)) return NULL; @@ -896,15 +893,17 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, } static struct page *follow_pmd_mask(struct vm_area_struct *vma, - unsigned long address, pud_t *pudp, - unsigned int flags, - unsigned long *page_mask) + unsigned long address, pud_t *pudp, pud_t pud, + unsigned int flags, unsigned long *page_mask) { pmd_t *pmd, pmdval; spinlock_t *ptl; struct page *page; struct mm_struct *mm = vma->vm_mm; + if (unlikely(pud_bad(pud))) + return no_page_table(vma, flags, address); + pmd = pmd_offset(pudp, address); pmdval = pmdp_get_lockless(pmd); if (pmd_none(pmdval)) @@ -953,18 +952,23 @@ static struct page *follow_pud_mask(struct vm_area_struct *vma, pud = pudp_get(pudp); if (!pud_present(pud)) return no_page_table(vma, flags, address); - if (pud_leaf(pud)) { - ptl = pud_lock(mm, pudp); - page = follow_huge_pud(vma, address, pudp, flags, page_mask); + if (!pud_leaf(pud)) + return follow_pmd_mask(vma, address, pudp, pud, flags, page_mask); + + ptl = pud_lock(mm, pudp); + pud = *pudp; + if (unlikely(!pud_present(pud))) { spin_unlock(ptl); - if (page) - return page; return no_page_table(vma, flags, address); } - if (unlikely(pud_bad(pud))) - return no_page_table(vma, flags, address); + if (unlikely(!pud_leaf(pud))) { + spin_unlock(ptl); + return follow_pmd_mask(vma, address, pudp, pud, flags, page_mask); + } - return follow_pmd_mask(vma, address, pudp, flags, page_mask); + page = follow_huge_pud(vma, address, pudp, flags, page_mask); + spin_unlock(ptl); + return page; } static struct page *follow_p4d_mask(struct vm_area_struct *vma, -- 2.43.0