From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 88C35D2FED9 for ; Tue, 27 Jan 2026 19:29:57 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id DD6666B0089; Tue, 27 Jan 2026 14:29:56 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D9E026B008A; Tue, 27 Jan 2026 14:29:56 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id CA0506B008C; Tue, 27 Jan 2026 14:29:56 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id BD2896B0089 for ; Tue, 27 Jan 2026 14:29:56 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 66C8E160216 for ; Tue, 27 Jan 2026 19:29:56 +0000 (UTC) X-FDA: 84378733992.03.EF2EFF8 Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf27.hostedemail.com (Postfix) with ESMTP id D90094000F for ; Tue, 27 Jan 2026 19:29:54 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=uzu2dY0F; spf=pass (imf27.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1769542194; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=kLseMfE2LRuo3JxDLOr0OXcWO0lmhSYypQgOjOmlOCg=; b=KQQjuFGvv+I0Eifr+NAqhXOCUXZ7GSAyj+QCQN1fkkzvgDV5S3Z7HUkHFEel1wEAaRAmZp J4OQh5hOF/wel/Bxvvw9XiRVYa41GnTFK16QuCNRs1vTn5H3w+px6lj08oQlBGP77MhSw2 yvoG0ndrTSe5FTPtMmRsiJbQUobpy9c= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=uzu2dY0F; spf=pass (imf27.hostedemail.com: domain of rppt@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1769542194; a=rsa-sha256; cv=none; b=QcsIxPg/301NQ2EcerE2SuNrhU6KmXiU6lM+ngOiXNmpUQoX9bAZ4OwS7tN/wWbKbCoCPt T/DVVtR6Ys6Obhso9K6D55bCjNXLosFDybwCgN8YsIsum4EF2/ogByms/vcewyYjtVZbnW f01RCt1oZpGqVggezCmOIGIi0fZXIrc= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id D9F5C601EB; Tue, 27 Jan 2026 19:29:53 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D53D3C19425; Tue, 27 Jan 2026 19:29:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1769542193; bh=aI4WO62kph2VvKe2gJ7QoMhXLXNy49H9C+58Y9P8ebA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=uzu2dY0FD8NP7vGfp5IudjeX8x6QiJOSfV1oxxuPXDUvu4rBKpUTNA49h5T9Wohpy pfEABMoxK6o/yC7roNa0yXjcHxBqwtIkm+UYpNDDQd1qRNy4ch60sgcDSqaVtG27wK K+UqBFc5dhddJewp0K/vzuLPF2PxpQi8HyATmV0Xi9XEzGTqVFNmA9w4LSuWcFXoVg QrYaAotmrdV0CDUshJOjvcVA2VrJFYEjysfOFyw5eFeR2wtvfX00eoewjFdNTtWcua +mBnHhBZ1o53N7kxZ4CnCivm92wleRp8YgLjcWxCGw1GfNjWI6wCViPGzu/VwKzk7f /HCrBMvTm8PjQ== From: Mike Rapoport To: linux-mm@kvack.org Cc: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH RFC 01/17] userfaultfd: introduce mfill_copy_folio_locked() helper Date: Tue, 27 Jan 2026 21:29:20 +0200 Message-ID: <20260127192936.1250096-2-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260127192936.1250096-1-rppt@kernel.org> References: <20260127192936.1250096-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: zcz5xecbmj9xttyhhxsfem3a1hwrqhyk X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: D90094000F X-HE-Tag: 1769542194-929160 X-HE-Meta: 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 S3RAcSZ6 H5PRiI6n93Kl3/9vJSDBkDqXxsnwWUAAXlAuVK1Pq+52DHPjuZzWFrYUH8PqPbUMCe90tQ8hyJ4ynwpf/ydAFaGlyYhIOeiKERG082nV9xA15yPArWT+7Avzlr4rpk5DAx2W4WKliM4j6SLpt1ZSI4HHgLGIzooKWQJ+n2vFW481xnvrJi6LPgxGTyNgzrGlMauRHhHWip0Qzb49PAjs7U7ycPC5w3KHZ/7qNRw8qzhkOEiXNyD/ZjqNqHhOV7amXUDk2SCE1aDnlXtGiDCy88KCXvw== 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: From: "Mike Rapoport (Microsoft)" Split copying of data when locks held from mfill_atomic_pte_copy() into a helper function mfill_copy_folio_locked(). This makes improves code readability and makes complex mfill_atomic_pte_copy() function easier to comprehend. No functional change. Signed-off-by: Mike Rapoport (Microsoft) --- mm/userfaultfd.c | 59 ++++++++++++++++++++++++++++-------------------- 1 file changed, 35 insertions(+), 24 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index e6dfd5f28acd..a0885d543f22 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -238,6 +238,40 @@ int mfill_atomic_install_pte(pmd_t *dst_pmd, return ret; } +static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr) +{ + void *kaddr; + int ret; + + kaddr = kmap_local_folio(folio, 0); + /* + * The read mmap_lock is held here. Despite the + * mmap_lock being read recursive a deadlock is still + * possible if a writer has taken a lock. For example: + * + * process A thread 1 takes read lock on own mmap_lock + * process A thread 2 calls mmap, blocks taking write lock + * process B thread 1 takes page fault, read lock on own mmap lock + * process B thread 2 calls mmap, blocks taking write lock + * process A thread 1 blocks taking read lock on process B + * process B thread 1 blocks taking read lock on process A + * + * Disable page faults to prevent potential deadlock + * and retry the copy outside the mmap_lock. + */ + pagefault_disable(); + ret = copy_from_user(kaddr, (const void __user *) src_addr, + PAGE_SIZE); + pagefault_enable(); + kunmap_local(kaddr); + + if (ret) + return -EFAULT; + + flush_dcache_folio(folio); + return ret; +} + static int mfill_atomic_pte_copy(pmd_t *dst_pmd, struct vm_area_struct *dst_vma, unsigned long dst_addr, @@ -245,7 +279,6 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd, uffd_flags_t flags, struct folio **foliop) { - void *kaddr; int ret; struct folio *folio; @@ -256,27 +289,7 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd, if (!folio) goto out; - kaddr = kmap_local_folio(folio, 0); - /* - * The read mmap_lock is held here. Despite the - * mmap_lock being read recursive a deadlock is still - * possible if a writer has taken a lock. For example: - * - * process A thread 1 takes read lock on own mmap_lock - * process A thread 2 calls mmap, blocks taking write lock - * process B thread 1 takes page fault, read lock on own mmap lock - * process B thread 2 calls mmap, blocks taking write lock - * process A thread 1 blocks taking read lock on process B - * process B thread 1 blocks taking read lock on process A - * - * Disable page faults to prevent potential deadlock - * and retry the copy outside the mmap_lock. - */ - pagefault_disable(); - ret = copy_from_user(kaddr, (const void __user *) src_addr, - PAGE_SIZE); - pagefault_enable(); - kunmap_local(kaddr); + ret = mfill_copy_folio_locked(folio, src_addr); /* fallback to copy_from_user outside mmap_lock */ if (unlikely(ret)) { @@ -285,8 +298,6 @@ static int mfill_atomic_pte_copy(pmd_t *dst_pmd, /* don't free the page */ goto out; } - - flush_dcache_folio(folio); } else { folio = *foliop; *foliop = NULL; -- 2.51.0