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 9C29AFB3CF8 for ; Mon, 30 Mar 2026 10:11:37 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 118726B0095; Mon, 30 Mar 2026 06:11:37 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 0C87F6B0096; Mon, 30 Mar 2026 06:11:37 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ED3376B0098; Mon, 30 Mar 2026 06:11:36 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id D92C06B0095 for ; Mon, 30 Mar 2026 06:11:36 -0400 (EDT) Received: from smtpin10.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 85460140606 for ; Mon, 30 Mar 2026 10:11:36 +0000 (UTC) X-FDA: 84602312592.10.53B5A4C Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf02.hostedemail.com (Postfix) with ESMTP id C0ED98000A for ; Mon, 30 Mar 2026 10:11:34 +0000 (UTC) Authentication-Results: imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=vNyD+lRi; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1774865494; 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=/fVNQITXaKPhp1TvGhahEVbTKg2c4l7V/Wc6cTAIBa0=; b=ZIpGGldSHrRLfS3CprqiU3fPz+OM4T8gDm6nyyz8MJtjBihmKHBO96FvQX5SBAYNao0Xgr tzCe99by8BC5wAoLo9iWao2VPUnmxCQoHTk1H1vuH0y3xE5LwH7L1dji46XaExUqQUERGa 1XeZ3Px5msYrSxON47zMlZQ8fzTLSd8= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774865494; a=rsa-sha256; cv=none; b=KlTKVhdDRaQ45yQ+WjSGVh8R1MAIrUKreaCZ07rQF47yRMRcYrMh9+B/GQkdPu7nv7EzQh EBV2ATtxLsEhcHYR3vB+o84vCdmzkJ48e5ud7cH1Tp1sxJYQ19YXvsRwfs7k17lswNXVN/ apoXGjsG2YwXJDp1UBdbkuxvCObAX+c= ARC-Authentication-Results: i=1; imf02.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=vNyD+lRi; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf02.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id B44AF432E6; Mon, 30 Mar 2026 10:11:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 62E06C4AF09; Mon, 30 Mar 2026 10:11:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774865493; bh=QyXpu9HXbfbZXv1V/Q6cFWUb/O2hxT2SCUEnl/mL9Tg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=vNyD+lRitJL6FQ08aJ2Ko9YEkn9XcqCTCToMIMy6KXBGYHirerrqpnx9wQJ/lbQUf jrjAH/939HGIiB+8//xJ6BkneVvgQgOOgrdOykR4LH2DxFcm84JgXOdgO6R6qN3eI1 fvzfe5DRsDPoqMPWtX4PgjizstOvrWWqRw4kYAJ+vnLsPYo02rCuCY0ghBouNvClfw nbZvA/MDezrrO0jmOynPpaB4RfA6Zm3JCOPztbjhB2LpcahiUwF/LJkbKbNDyoO0zo S7kU7amZbd7ez6V+LWcgIvyX25AoJjwsorPuTIcrD46phatb3RO/99PEaJpHoDmI9f AG1AA5cDImkQA== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Andrei Vagin , Axel Rasmussen , Baolin Wang , David Hildenbrand , Harry Yoo , Hugh Dickins , James Houghton , "Liam R. Howlett" , "Lorenzo Stoakes (Oracle)" , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , Muchun Song , Nikita Kalyazin , Oscar Salvador , Paolo Bonzini , Peter Xu , Sean Christopherson , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , kvm@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v3 01/15] userfaultfd: introduce mfill_copy_folio_locked() helper Date: Mon, 30 Mar 2026 13:11:02 +0300 Message-ID: <20260330101116.1117699-2-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260330101116.1117699-1-rppt@kernel.org> References: <20260330101116.1117699-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: C0ED98000A X-Stat-Signature: r1fyhma1tbdfi1kn3zbanz5cin53q7t1 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1774865494-380945 X-HE-Meta: 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 5wYyJaty qukpHpBs7soXzXnXeSwsZyOKQGC4xb+lU9Bi462HoxBV/WkS3X+sauqm+XyhyrBVh5Gs6A3Y3CLlECovMyfPopPgB45alYLvndhhaPdyju6B0W7XvGv9tvjd1i67N4oAkVuF74qIjMbDllXURc01S0ivkiKwHn4BnIDQ9p0j0sFsGoFpX3C7r2B7nKeKgowqc3P09u+xSoJDlGw9CIgGs1E9gdoyBFd7Q9ndiGSFVuQxqzDClzAU+Xa6Ic3OCJc5kJ9ak6igVHLgfRCx/zFDSNDXq8rUsY6EXUEbeuaBbcBuKYZMLSbp8jiG7BA== 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) Acked-by: Peter Xu Reviewed-by: David Hildenbrand (Arm) --- mm/userfaultfd.c | 59 ++++++++++++++++++++++++++++-------------------- 1 file changed, 35 insertions(+), 24 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index 927086bb4a3c..32637d557c95 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; -- 2.53.0