From nobody Mon Feb 9 17:37:10 2026 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass(p=quarantine dis=none) header.from=virtuozzo.com ARC-Seal: i=1; a=rsa-sha256; t=1617211788; cv=none; d=zohomail.com; s=zohoarc; b=A25ULb4BoTKcgw/wWzgEGMfTOpW4iO3us/XBoLgR8nQw77xvAl23AUVBoajYuBbC0b4it/toP1LYX21XOwMx5MhJ1giEi1aSrDZ4d26kF9YlsvBGR6WmYvhVmw9tivCeCFsiFHKahvccOpevyKBt0DmEmZ16ao3+0B92xPznCK8= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1617211788; h=Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To; bh=1AaVatpZSlATx99e4rvSYANsjd/KI7S4MT1FQQLheok=; b=SMRbHjm/leVMZCUAlELMS1HJOLhbszP3Jyw1M//IUUBT+5pHGK9DVmdr/MYKBkuFcZLtQliUDH7+zuGfcU4IkcIk6N6b6F5jgUi54LM+6w55yt/Cd16OE46UFuY8oxvltgus0M9g27LJH9r7tCkwGruU26tdllYRmMuZa8oPxyA= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=pass header.from= (p=quarantine dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1617211788610842.7029414308009; Wed, 31 Mar 2021 10:29:48 -0700 (PDT) Received: from localhost ([::1]:54870 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lRef5-0003Ir-8b for importer@patchew.org; Wed, 31 Mar 2021 13:29:47 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36672) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRedX-00020U-2R for qemu-devel@nongnu.org; Wed, 31 Mar 2021 13:28:11 -0400 Received: from relay.sw.ru ([185.231.240.75]:56394) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lRedT-0000pC-Nb for qemu-devel@nongnu.org; Wed, 31 Mar 2021 13:28:10 -0400 Received: from [192.168.15.162] (helo=andrey-MS-7B54.sw.ru) by relay.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1lRedQ-000D00-9R; Wed, 31 Mar 2021 20:28:04 +0300 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=virtuozzo.com; s=relay; h=MIME-Version:Message-Id:Date:Subject:From: Content-Type; bh=1AaVatpZSlATx99e4rvSYANsjd/KI7S4MT1FQQLheok=; b=NYFwCnFoACcI NoYdUFhAXsd5EeqQVKNcTE62ve4r1mQNntqCtjoAk2iY0Dtb/Vsiar01GhDEIK8hENAH3PHmnewo6 h7Jzx3JSwF1FB1VysCe4ZJKK2I9sHXJf+rbCOJcBMqFKFzdEj+rGJtoF1TPGDbiHTcI56pTbOo3R2 ApIMk=; From: Andrey Gruzdev To: qemu-devel@nongnu.org Cc: Den Lunev , Eric Blake , Paolo Bonzini , Juan Quintela , "Dr . David Alan Gilbert" , Markus Armbruster , Peter Xu , David Hildenbrand , Andrey Gruzdev Subject: [PATCH for-6.0 3/3] migration: Pre-fault memory before starting background snasphot Date: Wed, 31 Mar 2021 20:28:03 +0300 Message-Id: <20210331172803.87756-4-andrey.gruzdev@virtuozzo.com> X-Mailer: git-send-email 2.27.0 In-Reply-To: <20210331172803.87756-1-andrey.gruzdev@virtuozzo.com> References: <20210331172803.87756-1-andrey.gruzdev@virtuozzo.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=185.231.240.75; envelope-from=andrey.gruzdev@virtuozzo.com; helo=relay.sw.ru X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: pass (identity @virtuozzo.com) Content-Type: text/plain; charset="utf-8" This commit solves the issue with userfault_fd WP feature that background snapshot is based on. For any never poluated or discarded memory page, the UFFDIO_WRITEPROTECT ioctl() would skip updating PTE for that page, thereby loosing WP setting for it. So we need to pre-fault pages for each RAM block to be protected before making a userfault_fd wr-protect ioctl(). Signed-off-by: Andrey Gruzdev Reported-by: David Hildenbrand Reviewed-by: David Hildenbrand --- migration/migration.c | 6 ++++++ migration/ram.c | 48 +++++++++++++++++++++++++++++++++++++++++++ migration/ram.h | 1 + 3 files changed, 55 insertions(+) diff --git a/migration/migration.c b/migration/migration.c index be4729e7c8..71bce15a1b 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -3827,6 +3827,12 @@ static void *bg_migration_thread(void *opaque) =20 update_iteration_initial_status(s); =20 + /* + * Prepare for tracking memory writes with UFFD-WP - populate + * RAM pages before protecting. + */ + ram_write_tracking_prepare(); + qemu_savevm_state_header(s->to_dst_file); qemu_savevm_state_setup(s->to_dst_file); =20 diff --git a/migration/ram.c b/migration/ram.c index 40e78952ad..24c8627214 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -1560,6 +1560,54 @@ out: return ret; } =20 +/* + * ram_block_populate_pages: populate memory in the RAM block by reading + * an integer from the beginning of each page. + * + * Since it's solely used for userfault_fd WP feature, here we just + * hardcode page size to qemu_real_host_page_size. + * + * @bs: RAM block to populate + */ +static void ram_block_populate_pages(RAMBlock *bs) +{ + char *ptr =3D (char *) bs->host; + + for (ram_addr_t offset =3D 0; offset < bs->used_length; + offset +=3D qemu_real_host_page_size) { + char tmp =3D *(ptr + offset); + /* Don't optimize the read out */ + asm volatile("" : "+r" (tmp)); + } +} + +/* + * ram_write_tracking_prepare: prepare for UFFD-WP memory tracking + */ +void ram_write_tracking_prepare(void) +{ + RAMBlock *bs; + + RCU_READ_LOCK_GUARD(); + + RAMBLOCK_FOREACH_NOT_IGNORED(bs) { + /* Nothing to do with read-only and MMIO-writable regions */ + if (bs->mr->readonly || bs->mr->rom_device) { + continue; + } + + /* + * Populate pages of the RAM block before enabling userfault_fd + * write protection. + * + * This stage is required since ioctl(UFFDIO_WRITEPROTECT) with + * UFFDIO_WRITEPROTECT_MODE_WP mode setting would silently skip + * pages with pte_none() entries in page table. + */ + ram_block_populate_pages(bs); + } +} + /* * ram_write_tracking_start: start UFFD-WP memory tracking * diff --git a/migration/ram.h b/migration/ram.h index 6378bb3ebc..4833e9fd5b 100644 --- a/migration/ram.h +++ b/migration/ram.h @@ -82,6 +82,7 @@ void colo_incoming_start_dirty_log(void); /* Background snapshot */ bool ram_write_tracking_available(void); bool ram_write_tracking_compatible(void); +void ram_write_tracking_prepare(void); int ram_write_tracking_start(void); void ram_write_tracking_stop(void); =20 --=20 2.27.0