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 X-Spam-Level: X-Spam-Status: No, score=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 C730EC433DF for ; Thu, 4 Jun 2020 13:27:42 +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 9051620772 for ; Thu, 4 Jun 2020 13:27:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="O0hfS5Gi" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9051620772 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:48006 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jgpuH-0002xd-TU for qemu-devel@archiver.kernel.org; Thu, 04 Jun 2020 09:27:41 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:59732) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jgpti-0002Xy-EE for qemu-devel@nongnu.org; Thu, 04 Jun 2020 09:27:06 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:48868 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jgpth-0004HZ-Bw for qemu-devel@nongnu.org; Thu, 04 Jun 2020 09:27:06 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591277224; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2uzJu2uEpKt1MtBeOPW/VvzZHQio3U35JVuAKtkhcqw=; b=O0hfS5GiRsfB7eZBRggYO+ONw4ISe2XcLEXzZtOzI1V4UogE+/8ygJ94yABNSp1zi/L0uv +oHaESlEJSgtF1RCjYsWCWx5HZJ80S72QCij94CCeMsXyYd588izl/ftSTUJSY04aidsmA nU4jsLwjQYePL3dGXMczc9aB+6tzwbg= 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-309-3sca0TvVN_C_LShCxgtalQ-1; Thu, 04 Jun 2020 09:27:02 -0400 X-MC-Unique: 3sca0TvVN_C_LShCxgtalQ-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D826F102CC43; Thu, 4 Jun 2020 13:27:01 +0000 (UTC) Received: from work-vm (ovpn-114-247.ams2.redhat.com [10.36.114.247]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5D9FD5FC34; Thu, 4 Jun 2020 13:26:38 +0000 (UTC) Date: Thu, 4 Jun 2020 14:26:35 +0100 From: "Dr. David Alan Gilbert" To: Alex =?iso-8859-1?Q?Benn=E9e?= Subject: Re: [RFC PATCH] hw/virtio/vhost: re-factor vhost-section and allow DIRTY_MEMORY_CODE Message-ID: <20200604132635.GG2851@work-vm> References: <20200604111323.7458-1-alex.bennee@linaro.org> MIME-Version: 1.0 In-Reply-To: <20200604111323.7458-1-alex.bennee@linaro.org> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Content-Disposition: inline Received-SPF: pass client-ip=207.211.31.81; envelope-from=dgilbert@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/04 01:31:23 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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, 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_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, T_HK_NAME_DR=0.01, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: , Cc: qemu-devel@nongnu.org, Stefan Hajnoczi , "Michael S . Tsirkin" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Alex Bennée (alex.bennee@linaro.org) wrote: > The purpose of vhost_section is to identify RAM regions that need to > be made available to a vhost client. However when running under TCG > all RAM sections have DIRTY_MEMORY_CODE set which leads to problems > down the line. The original comment implies VGA regions are a problem > but doesn't explain why vhost has a problem with it. > > Re-factor the code so: > > - steps are clearer to follow > - reason for rejection is recorded in the trace point > - we allow DIRTY_MEMORY_CODE when TCG is enabled The problem with VGA is that a VGA page can become mapped and unmapped under the control of the guest; somewhere in a low address. This tends to break hugepage mappings. For vhost-user, and in particular vhost-user-postcopy this means it fails the mapping on the vhost-user client. However the other problem is that with vhost-user, the vhost-user client is changing memory; and won't mark the pages as dirty - except for migration (I'm not clear if vhost kernel does this). So TCG won't notice a page that's been changed by the driver; now in most cases it's rare for a device to be writing directly into a page you're going to execute out of, but it's not unknown. So, as it is, any area that's expecting to get non-migration dirty notifications is going to be disappointed by a vhost-user backend. Dave > Signed-off-by: Alex Bennée > Cc: Michael S. Tsirkin > Cc: Dr. David Alan Gilbert > Cc: Stefan Hajnoczi > --- > hw/virtio/vhost.c | 46 ++++++++++++++++++++++++++++++++-------------- > 1 file changed, 32 insertions(+), 14 deletions(-) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > index aff98a0ede5..f81fc87e74c 100644 > --- a/hw/virtio/vhost.c > +++ b/hw/virtio/vhost.c > @@ -27,6 +27,7 @@ > #include "migration/blocker.h" > #include "migration/qemu-file-types.h" > #include "sysemu/dma.h" > +#include "sysemu/tcg.h" > #include "trace.h" > > /* enabled until disconnected backend stabilizes */ > @@ -403,26 +404,43 @@ static int vhost_verify_ring_mappings(struct vhost_dev *dev, > return r; > } > > +/* > + * vhost_section: identify sections needed for vhost access > + * > + * We only care about RAM sections here (where virtqueue can live). If > + * we find one we still allow the backend to potentially filter it out > + * of our list. > + */ > static bool vhost_section(struct vhost_dev *dev, MemoryRegionSection *section) > { > - bool result; > - bool log_dirty = memory_region_get_dirty_log_mask(section->mr) & > - ~(1 << DIRTY_MEMORY_MIGRATION); > - result = memory_region_is_ram(section->mr) && > - !memory_region_is_rom(section->mr); > - > - /* Vhost doesn't handle any block which is doing dirty-tracking other > - * than migration; this typically fires on VGA areas. > - */ > - result &= !log_dirty; > + enum { OK = 0, NOT_RAM, DIRTY, FILTERED } result = NOT_RAM; > + > + if (memory_region_is_ram(section->mr) && !memory_region_is_rom(section->mr)) { > + uint8_t dirty_mask = memory_region_get_dirty_log_mask(section->mr); > + uint8_t handled_dirty; > > - if (result && dev->vhost_ops->vhost_backend_mem_section_filter) { > - result &= > - dev->vhost_ops->vhost_backend_mem_section_filter(dev, section); > + /* > + * Vhost doesn't handle any block which is doing dirty-tracking other > + * than migration; this typically fires on VGA areas. However > + * for TCG we also do dirty code page tracking which shouldn't > + * get in the way. > + */ > + handled_dirty = (1 << DIRTY_MEMORY_MIGRATION); > + if (tcg_enabled()) { > + handled_dirty |= (1 << DIRTY_MEMORY_CODE); > + } > + if (dirty_mask & ~handled_dirty) { > + result = DIRTY; > + } else if (dev->vhost_ops->vhost_backend_mem_section_filter && > + !dev->vhost_ops->vhost_backend_mem_section_filter(dev, section)) { > + result = FILTERED; > + } else { > + result = OK; > + } > } > > trace_vhost_section(section->mr->name, result); > - return result; > + return result == OK; > } > > static void vhost_begin(MemoryListener *listener) > -- > 2.20.1 > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK