From nobody Sat Feb 7 07:09:48 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=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1617818744; cv=none; d=zohomail.com; s=zohoarc; b=hI/vrQleFZsLCML+/7aOgu8k1g4uoSI1xtHVHksc2DlRfqmj9R+fYGmFLa1DPZctUcAljqhxdvJEw95HSg2nlHJGHrNvCPOC9BJQIgLi7gnwOMNhTYu3Ilzq2/084hJvqGXPKZcNlqGJIhYmxuCU3f5CZiL0fLLq1IDrtmm9ohE= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1617818744; h=Content-Type:Content-Transfer-Encoding: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=a5Vy5QOQ+5HwVDlIw7ETRAG3mK0m+9IKLmDtnDNiCws=; b=la7iw939hJPZ1EIqbUpot1TcRE3FMYwrY+85nb5goAcU7o8YktuXN8XYr8vPGFhNxR8k/Uw5vXo6ldFjLxvB/OGlDEcthW6ReLg3xXU8MKZwRSGsxr+pouNJRUZV8mSWlK5DT/SxoDbEGrIJzs1fY5pwZSeCjon9G7Yun3s+JmM= 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=none 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 1617818744899561.8912903679302; Wed, 7 Apr 2021 11:05:44 -0700 (PDT) Received: from localhost ([::1]:44900 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lUCYh-00065M-Lk for importer@patchew.org; Wed, 07 Apr 2021 14:05:43 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49004) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUCNu-0002JC-BK for qemu-devel@nongnu.org; Wed, 07 Apr 2021 13:54:34 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:50456) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUCNq-0005Wa-UE for qemu-devel@nongnu.org; Wed, 07 Apr 2021 13:54:33 -0400 Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-512-fM44LD29NmWnjIhhXdwC9w-1; Wed, 07 Apr 2021 13:54:25 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 519D51922965; Wed, 7 Apr 2021 17:54:24 +0000 (UTC) Received: from dgilbert-t580.localhost (ovpn-115-14.ams2.redhat.com [10.36.115.14]) by smtp.corp.redhat.com (Postfix) with ESMTP id 75A7E10013D7; Wed, 7 Apr 2021 17:54:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1617818069; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=a5Vy5QOQ+5HwVDlIw7ETRAG3mK0m+9IKLmDtnDNiCws=; b=I/j1OV9Rn30oo5cz/A8lIQ3bdLomm71wCbSE7XJLuOrgPm+JttP+WlKHO4CJFVz5K1or7H uj6CzEqMYZ9zyCSNYICAxqdDAfh+rUgA5kpacSf2j+Rxsq5mb//HqXWEz7XxLSKrVX6E3M kzu6ZxlCqlcZCdVdQFpnZGzjZE4j1tQ= X-MC-Unique: fM44LD29NmWnjIhhXdwC9w-1 From: "Dr. David Alan Gilbert (git)" To: qemu-devel@nongnu.org, andrey.gruzdev@virtuozzo.com, huangy81@chinatelecom.cn Subject: [PULL 4/6] migration: Pre-fault memory before starting background snasphot Date: Wed, 7 Apr 2021 18:54:14 +0100 Message-Id: <20210407175416.201555-5-dgilbert@redhat.com> In-Reply-To: <20210407175416.201555-1-dgilbert@redhat.com> References: <20210407175416.201555-1-dgilbert@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dgilbert@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com 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=63.128.21.124; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, 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 @redhat.com) Content-Type: text/plain; charset="utf-8" From: Andrey Gruzdev 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(). Fixes: 278e2f551a095b234de74dca9c214d5502a1f72c (migration: support UFFD write fault processing in ram_save_iterate()) Signed-off-by: Andrey Gruzdev Reported-by: David Hildenbrand Reviewed-by: David Hildenbrand Message-Id: <20210401092226.102804-4-andrey.gruzdev@virtuozzo.com> Signed-off-by: Dr. David Alan Gilbert dgilbert: Bodged ifdef __linux__ on ram_write_tracking_prepare, should really go in a stub --- migration/migration.c | 8 +++++++ migration/ram.c | 49 +++++++++++++++++++++++++++++++++++++++++++ migration/ram.h | 1 + 3 files changed, 58 insertions(+) diff --git a/migration/migration.c b/migration/migration.c index be4729e7c8..8ca034136b 100644 --- a/migration/migration.c +++ b/migration/migration.c @@ -3827,6 +3827,14 @@ 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. + */ +#ifdef __linux__ + ram_write_tracking_prepare(); +#endif + 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..7e2bc0fdd3 100644 --- a/migration/ram.c +++ b/migration/ram.c @@ -1560,6 +1560,55 @@ 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 2.31.1