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 81170CC6B00 for ; Thu, 2 Apr 2026 04:12:44 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CBA0A6B0095; Thu, 2 Apr 2026 00:12:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id C6B7F6B0096; Thu, 2 Apr 2026 00:12:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BA8EE6B0098; Thu, 2 Apr 2026 00:12:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id ABBD46B0095 for ; Thu, 2 Apr 2026 00:12:43 -0400 (EDT) Received: from smtpin12.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 3F2AB58941 for ; Thu, 2 Apr 2026 04:12:43 +0000 (UTC) X-FDA: 84612294606.12.926319D Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf19.hostedemail.com (Postfix) with ESMTP id AF2691A000E for ; Thu, 2 Apr 2026 04:12:41 +0000 (UTC) Authentication-Results: imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=nb8I1ZCl; spf=pass (imf19.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=rppt@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Authentication-Results: i=1; imf19.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=nb8I1ZCl; spf=pass (imf19.hostedemail.com: domain of rppt@kernel.org designates 172.234.252.31 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=1775103161; a=rsa-sha256; cv=none; b=c3MQyvbOYUeSHHXzvE1lin/iphHkOwaf/mW9lfJdJmTQFPeU0dtShTaasfuqjrMQfLTQOG DQ8Td1jSkoTg80aXBksKVervd3z0xbvMyiNExOfRw1hjJ91d9Jf2aDC0IUJmINqWGxGRCb tPHCV8b7cQXeWTwL22OSfseNdvA/d30= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1775103161; 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=IoIqhmLWfmA8QbUo+j+cNUM7Sd55lp28uew+lrrL5F6QsgMTXXrfnbHEur3Q2cVtNBFjQJ DX5J/Pa4iX3X3g2FvCkQPj8SQzJ47U3n7MwuS28M074/i0Cj+unnxJfYI5ZR3fAZ6sflzG 9cebZtxD6E7S96xNHh/yKilUA3mdEaU= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id C5D51437A3; Thu, 2 Apr 2026 04:12:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63406C19424; Thu, 2 Apr 2026 04:12:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1775103160; bh=5SzGyiFXZk7l7ucReQ40iRkaPGcy2CcX6r/21eMkk2I=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nb8I1ZClTDvPDGKxLBHAn3NCmEgGMU/AnhVCCtaCop4gpA26w+lGeVCMGevXI03Z7 ouBoPoNz1kFRSoUMyRWbj1Uwc6X15ppsOD1eoF7JwetBZZkgI1ZHeU62VnAhCzCpdV CgElsa9j93OX2uIsN8NVJVA1uAtcfmhXIYHd7hzfv5sMbFTLGYOor6KuIM1dcmms/p 2a0yzV0XuFg42PyKC66b+CK3kiM9NjbZh8qz+GI0RQX8A0MyIF++VDQ24nPRn6dKU8 da5kdRFrmmwwVlmhYmd9FFBvegTJuX2GBYV+d7U1E8pq8yGjXiCQIJ/Y82soByxhIj z1dktaok5sFiA== 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 v4 05/15] userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() Date: Thu, 2 Apr 2026 07:11:46 +0300 Message-ID: <20260402041156.1377214-6-rppt@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260402041156.1377214-1-rppt@kernel.org> References: <20260402041156.1377214-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: AF2691A000E X-Stat-Signature: i9f9sbikx1q4yjjb7odk6m7s8ruhca3k X-Rspam-User: X-HE-Tag: 1775103161-459958 X-HE-Meta: U2FsdGVkX1+GGzGPABsyMRD/+D9uMYiKzHcj40ELStFtc8dcd0Mt7uYtIe5zbWU9lNqTooGOMNrCLQp/gG7jnjpfC6ccEQFHEphM2Xuqk49GE4ex+s0BByCt/bA4+N8L4BlkUcAoxfI9KXtj77qdQoBT4411+wYYCkVLmAn4V/ZGhPjNSKQP06axReta3AXvyu0XLsZe5S0w2tKad83X4AyvooXcGbHZ/mhMWKGQE7i68QlgLPzNJoB+V8bAdaNZeAG/YtkFvn5UqEtbwlKNhoQdIYKraHoj12JKlfPtrFw1RdepBHvn8CYEKKorZST7cgijDtpeA3KNAdRE9l4holbZOVa6fBgD+XwJhjK6FKeYtPtU7f/b82UnFRUj8sC31B5zwLCATOdRurwOBrLZWiqOQoKi7kuN8evd4qLL1qd6vxmql9j4FezLTe2dqe016CSusD5LyCcSze4k7leFeT89ARNDwz1c1U7zJ4BTVbE+Y9qde4HMW1BqzBUFSTC7kB5uENzpu397b2LVpAoeNdBfuYxJmYrB59Abe/8j1SKMKf12K+jmfa8CHFCGMuwMORagbvWL5/Bw5COB4rasNDZc3rUmvUff3WL0mSzxEaUrxTs4oGnMcBoCK38SC+3BILPPHveqFB9l7H+piGFJhRhF4Uzx6L3o2/j1PmJsrHt6V4vGh5nRzTxHBDcP0nV8gdLBPaBol/nDfDecHI7qc1LclPgvBQbEfLEMeAMIP4ITIOcd6eDY3GX7nKfaTwesVcAb/oYTMQ8wq4cMAaz4IAor+1VfOL3kR+JBhi8U+Hcfr+LB+tv2r4dx24kbaFx6R/5FE9XGyfee4RFUhQLRQu7bRwT5AKJFrXwfHB/tahmgP/4ajEl2ltzHMmwCC5o3b1CAhJD4C19ULt9MDD3sO1lQ2T8OzjYv//aQwJTFpyRQz/vdGq/aKLMU70YxLMzy1VcuCPPC9bMXLTFcTkL YGcRmjhQ xDo7ErXEzY6D9CaM= 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