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 54DA9FB3CF7 for ; Mon, 30 Mar 2026 10:12:04 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BEF086B009D; Mon, 30 Mar 2026 06:12:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id B77C76B009E; Mon, 30 Mar 2026 06:12:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A66BE6B009F; Mon, 30 Mar 2026 06:12:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 92B456B009D for ; Mon, 30 Mar 2026 06:12:03 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay02.hostedemail.com (Postfix) with ESMTP id 533E113B9D6 for ; Mon, 30 Mar 2026 10:12:03 +0000 (UTC) X-FDA: 84602313726.18.C337A06 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf20.hostedemail.com (Postfix) with ESMTP id 9090E1C0002 for ; Mon, 30 Mar 2026 10:12:01 +0000 (UTC) Authentication-Results: imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=rnZmUZP7; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1774865521; a=rsa-sha256; cv=none; b=On3Psj9Q3BOD2sEITXLQNodXxG3/55wloiJOy2RevS04Jjz6P9pCYnvAafqm5JO8FNI3+z 6NNOzqqtw8KNbJVTEEqiuc9p6uqyLYf09YjyDeYNiACPbXB7266kvRhJX2fgZYSDuOh4jx XL16y9SGjqhutP31FyeZPSDxGusSwVw= ARC-Authentication-Results: i=1; imf20.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=rnZmUZP7; dmarc=pass (policy=quarantine) header.from=kernel.org; spf=pass (imf20.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=1774865521; 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=KG9O15NEX//F7Y7M34uU3bVy0OPGvFNGxrIfN55SF7g=; b=C8r9Bi25oq/2fkNiICImLJr1ZDjoi3dgNqxFO0mUC222pccrFDUBo0548CUDt299T6JT4F c4egCo9iUIkzBLR1cHT4dgs7iWVMg5/R08VPhEsicIQyUZIHzkfyIbqomfVQZZlvpEk/Bo XPCRVzZUphFR0B7a8Y8QlazDWvcJWlY= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id AA081443BD; Mon, 30 Mar 2026 10:12:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 500A1C4AF09; Mon, 30 Mar 2026 10:11:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1774865520; bh=5SzGyiFXZk7l7ucReQ40iRkaPGcy2CcX6r/21eMkk2I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rnZmUZP7gvczpmYCEel4ZXmQ2PPmuQj3/XLGNLve0YawXSP2n2h581cordUCP7K2b MmmnEb7e8DcyW1uRo2AewcgnTOx9blnu4afb+Q6gn6po2hgdRBuRrJswZumlsmYQNN WYGrErDR5bviDJ6dVcSCtl71iYEOnC/KGr//7ne2uRD2lGWNH5EdqFy8ypdTN6NjbK wMigsbkomvod7dn/ko2q+w52YIV1vn+g4FPibveRYXwvjuSLuiL4fl4nvG3oPg8ZBe Vh0YR62YlJQBCLgTH39pGzGix1bhYmhld6ri6Jv3CHDGtgiWE7cMHSiyIKoqN90k+r gOXP70eeEkHwg== 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 05/15] userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() Date: Mon, 30 Mar 2026 13:11:06 +0300 Message-ID: <20260330101116.1117699-6-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: 9090E1C0002 X-Stat-Signature: 7zydy58syzcuzn4ey39exbyoim8ijdpk X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1774865521-592117 X-HE-Meta: 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 L2ptNf9K kTZV6vIKp55ljKlXyfVJLuwbPgse6+gcWJ21OluNOJSswGp9YKS0cIczqEHF4/xzc8pYGyXXQM5NLs5URb3JEwO/lGkC6i/+l7SVoAYVbvbzhnqOLx1YzTpVZcF1RpBgqn/9kmk9F093B6AbQcOAe1akPKDRsFyabCcKActVXCuRj3eslR4my7DppyvkH7o2pLzKSp2MUns6HLpRNbQWcUyMENGBdbruYUwxXwHzzKDcHJmJDSkf6ZXvTDzcJpHoA3RWhNG/6gaRgzVEdq4Pecxrq/fkk58yybHc4RYYJxY9phUaWoTO0sfGDK6DsQwoGxXTzoyp4zQ6iA9viq4P+bmp18GUjdXZ69ttRWyMKBf8Jn4I= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: "Mike Rapoport (Microsoft)" Implementation of UFFDIO_COPY for anonymous memory might fail to copy data from userspace buffer when the destination VMA is locked (either with mm_lock or with per-VMA lock). In that case, mfill_atomic() releases the locks, retries copying the data with locks dropped and then re-locks the destination VMA and re-establishes PMD. Since this retry-reget dance is only relevant for UFFDIO_COPY and it never happens for other UFFDIO_ operations, make it a part of mfill_atomic_pte_copy() that actually implements UFFDIO_COPY for anonymous memory. As a temporal safety measure to avoid breaking biscection mfill_atomic_pte_copy() makes sure to never return -ENOENT so that the loop in mfill_atomic() won't retry copiyng outside of mmap_lock. This is removed later when shmem implementation will be updated later and the loop in mfill_atomic() will be adjusted. [akpm@linux-foundation.org: update mfill_copy_folio_retry()] Link: https://lkml.kernel.org/r/20260316173829.1126728-1-avagin@google.com Link: https://lkml.kernel.org/r/20260306171815.3160826-6-rppt@kernel.org Signed-off-by: Mike Rapoport (Microsoft) Signed-off-by: Andrew Morton --- mm/userfaultfd.c | 75 ++++++++++++++++++++++++++++++++---------------- 1 file changed, 51 insertions(+), 24 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index c6a38db45343..82e1a3255e1e 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -405,35 +405,63 @@ static int mfill_copy_folio_locked(struct folio *folio, unsigned long src_addr) return ret; } +static int mfill_copy_folio_retry(struct mfill_state *state, struct folio *folio) +{ + unsigned long src_addr = state->src_addr; + void *kaddr; + int err; + + /* retry copying with mm_lock dropped */ + mfill_put_vma(state); + + kaddr = kmap_local_folio(folio, 0); + err = copy_from_user(kaddr, (const void __user *) src_addr, PAGE_SIZE); + kunmap_local(kaddr); + if (unlikely(err)) + return -EFAULT; + + flush_dcache_folio(folio); + + /* reget VMA and PMD, they could change underneath us */ + err = mfill_get_vma(state); + if (err) + return err; + + err = mfill_establish_pmd(state); + if (err) + return err; + + return 0; +} + static int mfill_atomic_pte_copy(struct mfill_state *state) { - struct vm_area_struct *dst_vma = state->vma; unsigned long dst_addr = state->dst_addr; unsigned long src_addr = state->src_addr; uffd_flags_t flags = state->flags; - pmd_t *dst_pmd = state->pmd; struct folio *folio; int ret; - if (!state->folio) { - ret = -ENOMEM; - folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, dst_vma, - dst_addr); - if (!folio) - goto out; + folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, state->vma, dst_addr); + if (!folio) + return -ENOMEM; - ret = mfill_copy_folio_locked(folio, src_addr); + ret = -ENOMEM; + if (mem_cgroup_charge(folio, state->vma->vm_mm, GFP_KERNEL)) + goto out_release; - /* fallback to copy_from_user outside mmap_lock */ - if (unlikely(ret)) { - ret = -ENOENT; - state->folio = folio; - /* don't free the page */ - goto out; - } - } else { - folio = state->folio; - state->folio = NULL; + ret = mfill_copy_folio_locked(folio, src_addr); + if (unlikely(ret)) { + /* + * Fallback to copy_from_user outside mmap_lock. + * If retry is successful, mfill_copy_folio_locked() returns + * with locks retaken by mfill_get_vma(). + * If there was an error, we must mfill_put_vma() anyway and it + * will take care of unlocking if needed. + */ + ret = mfill_copy_folio_retry(state, folio); + if (ret) + goto out_release; } /* @@ -443,17 +471,16 @@ static int mfill_atomic_pte_copy(struct mfill_state *state) */ __folio_mark_uptodate(folio); - ret = -ENOMEM; - if (mem_cgroup_charge(folio, dst_vma->vm_mm, GFP_KERNEL)) - goto out_release; - - ret = mfill_atomic_install_pte(dst_pmd, dst_vma, dst_addr, + ret = mfill_atomic_install_pte(state->pmd, state->vma, dst_addr, &folio->page, true, flags); if (ret) goto out_release; out: return ret; out_release: + /* Don't return -ENOENT so that our caller won't retry */ + if (ret == -ENOENT) + ret = -EFAULT; folio_put(folio); goto out; } -- 2.53.0