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 97985FCC048 for ; Fri, 6 Mar 2026 17:19:00 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id E73166B009E; Fri, 6 Mar 2026 12:18:59 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id E54826B009F; Fri, 6 Mar 2026 12:18:59 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D74136B00A0; Fri, 6 Mar 2026 12:18:59 -0500 (EST) 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 C905C6B009E for ; Fri, 6 Mar 2026 12:18:59 -0500 (EST) Received: from smtpin03.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay10.hostedemail.com (Postfix) with ESMTP id 9624CC236E for ; Fri, 6 Mar 2026 17:18:59 +0000 (UTC) X-FDA: 84516298398.03.6AF9B5B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf07.hostedemail.com (Postfix) with ESMTP id 148B540006 for ; Fri, 6 Mar 2026 17:18:57 +0000 (UTC) Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="L9/3UiF0"; spf=pass (imf07.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=1772817538; 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=ypXOy/46SJyEO8/XuqFJ1+QX6XByCxN8UdseGl4Tyhs=; b=KJxshjdeXXz8BTG6D4UJZcR/i4KpxKwFpHWtG4siK1RCy0Sf1SMyQjBMl2Z/mcd0HYuF80 BZAmkAD5KDNQY7NrA40g3hIpIDAf+n6BLJb4kHzfB0TYZN2XxMGZMKb8If4Y7I6FHkMeUW N20tSHtr/VRvH0IGXBwshqa47VoL3Mw= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1772817538; a=rsa-sha256; cv=none; b=trfUxK5A+qcvGWCayGXBBzEQzZ+arbCyyTRHuaXg7d4okH7Aly8D7dzjbj0aJBuHfcLK5K XMUfvj7wLitpfyPbltU+sJCbxXF+3ivD2/2ElyqvLrqTdGdceU9+m9p/OOme8uHaW1gAo1 81ugEjdvkVZane1S3o9tsviHcjZTTYk= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b="L9/3UiF0"; spf=pass (imf07.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 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 8F35A60018; Fri, 6 Mar 2026 17:18:57 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E93AC2BCB5; Fri, 6 Mar 2026 17:18:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772817537; bh=uK6YVn1uE8/KerH/03wILxjQbYg54EfQnPDfF+duTRs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=L9/3UiF0bLNrJW644W0ccpADpS02wFJO0vTsEAx70zQnWCc+CmzLC0z5GNaljf838 9kmqMyDToEUngqQ0VlIu9ohLy+iRzBw5PM10ms0ZQHGffSwdW7ZtQLvPOEb/LG72K5 Tyf2dRIFqQqYxpoPFkaaSXkl1Y3ixUfXKoG2LPnxrMu1X3zUB9mdO75veRF4I0Nxam i3rxEdp3qAx0Y5UmJj9Yx209e0qhdG6Ui7U2tA1sWXPKk8npq4f9C/K9lIebErZiRW mGCHmipp5578CvkR5Qrznyly///YQ/XqjCCFnDB4oUAP9zMjtseOfZO+kh8Dpt3KvP bjE4FGXWmF+vw== From: Mike Rapoport To: Andrew Morton Cc: Andrea Arcangeli , Axel Rasmussen , Baolin Wang , David Hildenbrand , Hugh Dickins , James Houghton , "Liam R. Howlett" , Lorenzo Stoakes , "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 v2 05/15] userfaultfd: retry copying with locks dropped in mfill_atomic_pte_copy() Date: Fri, 6 Mar 2026 19:18:05 +0200 Message-ID: <20260306171815.3160826-6-rppt@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260306171815.3160826-1-rppt@kernel.org> References: <20260306171815.3160826-1-rppt@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 148B540006 X-Stat-Signature: iyji7yt1r9e4heggkwzjxr3sbkujrkru X-HE-Tag: 1772817537-931090 X-HE-Meta: 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 kAvcbUpb tuWmnGffj6MmOPC9goW6WmdiAcSwD8CAVFcLwV9FUUwwQot6iW2SUZ9obM+w2MgL4idotx5xctPwhtKw473aXz1oC+/SqbBkfoepKYjaa4qzCtV1skHpR86/JgWVBO8pHhU0rLngSBFOsDO0dv/sjscnjnS/DbXt7EMLHL0SXfZtIdxpLbG9BLeHzRYnuLog0+2ALib52B/yg8otGPy8wBydhi1ZYHkeQaMFY/yqc4IwvdC07KRjlBa1uGelEKKLRp+oBHrjuz48eTaEty7C2iAjPPQ== 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. Signed-off-by: Mike Rapoport (Microsoft) --- mm/userfaultfd.c | 78 +++++++++++++++++++++++++++++++++--------------- 1 file changed, 54 insertions(+), 24 deletions(-) diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index baff11e83101..828f252c720c 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -159,6 +159,9 @@ static void uffd_mfill_unlock(struct vm_area_struct *vma) static void mfill_put_vma(struct mfill_state *state) { + if (!state->vma) + return; + up_read(&state->ctx->map_changing_lock); uffd_mfill_unlock(state->vma); state->vma = NULL; @@ -404,35 +407,63 @@ 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_get_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; } /* @@ -442,17 +473,16 @@ 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; } -- 2.51.0