From patchwork Fri Mar 19 14:52:49 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Andrey Gruzdev X-Patchwork-Id: 12151249 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-18.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 36EB8C433DB for ; Fri, 19 Mar 2021 14:57:55 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 90BA464ECF for ; Fri, 19 Mar 2021 14:57:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 90BA464ECF Authentication-Results: mail.kernel.org; dmarc=fail (p=quarantine dis=none) header.from=virtuozzo.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:57444 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lNGZV-0000wh-DZ for qemu-devel@archiver.kernel.org; Fri, 19 Mar 2021 10:57:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56574) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lNGUs-000461-Ls for qemu-devel@nongnu.org; Fri, 19 Mar 2021 10:53:06 -0400 Received: from relay.sw.ru ([185.231.240.75]:58482) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lNGUg-0003xP-W6 for qemu-devel@nongnu.org; Fri, 19 Mar 2021 10:53:06 -0400 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=SimcNVQPEgM4Z6Pf9qEYCzmMBCppX5iXrLbgjb+2yio=; b=rL8iBVLx/IfX KvfsaeK3XCuM3LJ3FPTzPlUqVHZv0JgSvGbM23DE1A2r7B8bbUTpTfk99l1MYEr81nTwwj0DwVlLq PRIG3TP81dm5Wz53atnqIJ5TO9N5Y+SNd7IBmSBAhs2Ys6o9IEcXONeJzQet3pgpRFDJH91okmwQu IrekQ=; Received: from [192.168.15.248] (helo=andrey-MS-7B54.sw.ru) by relay.sw.ru with esmtp (Exim 4.94) (envelope-from ) id 1lNGUY-00010K-1o; Fri, 19 Mar 2021 17:52:46 +0300 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 v1 3/3] migration: Pre-fault memory before starting background snasphot Date: Fri, 19 Mar 2021 17:52:49 +0300 Message-Id: <20210319145249.425189-4-andrey.gruzdev@virtuozzo.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210319145249.425189-1-andrey.gruzdev@virtuozzo.com> References: <20210319145249.425189-1-andrey.gruzdev@virtuozzo.com> MIME-Version: 1.0 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+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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 --- 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 32aee2c5bd..ae7855155f 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -3827,6 +3827,12 @@ static void *bg_migration_thread(void *opaque) update_iteration_initial_status(s); + /* + * 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); 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; } +/* + * 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 = (char *) bs->host; + + for (ram_addr_t offset = 0; offset < bs->used_length; + offset += qemu_real_host_page_size) { + char tmp = *(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);