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,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 E5DA6C433DF for ; Thu, 4 Jun 2020 13:08:46 +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 AFC1A206C3 for ; Thu, 4 Jun 2020 13:08:46 +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="ZFdtMUTO" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AFC1A206C3 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]:44524 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jgpbx-0003Ub-Td for qemu-devel@archiver.kernel.org; Thu, 04 Jun 2020 09:08:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57580) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jgpb6-0002y9-UV for qemu-devel@nongnu.org; Thu, 04 Jun 2020 09:07:55 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:59103 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 1jgpb5-0008U7-D5 for qemu-devel@nongnu.org; Thu, 04 Jun 2020 09:07:52 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1591276069; 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=/JitHzYwvkctS40xrSp6xh8/XQ/DVrvtNX6jSFMTroM=; b=ZFdtMUTO6fzKSUdPhpCI/bjFH/NRGaZ6z0U0M9AC5BZHz9OjdL8ffCi9ux0h2LUf17gBet DLhLASQXcAHndptZ3ww9CE0MWWuKSvMmw1pgldmai0+FjFGkZVMvgyI5SwYdJ3N3bkvhPu tjkNhJzHwvjBmZD8C7qKeoeEjHTvz2c= 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-320-Xe9m9VrMNj24yxg_Teo_LA-1; Thu, 04 Jun 2020 09:07:47 -0400 X-MC-Unique: Xe9m9VrMNj24yxg_Teo_LA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9A24A1883604; Thu, 4 Jun 2020 13:07:46 +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 D77EB891D6; Thu, 4 Jun 2020 13:07:31 +0000 (UTC) Date: Thu, 4 Jun 2020 14:07:29 +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: <20200604130729.GF2851@work-vm> References: <20200604111323.7458-1-alex.bennee@linaro.org> <20200604071504-mutt-send-email-mst@kernel.org> <87ftbb59vm.fsf@linaro.org> <20200604075020-mutt-send-email-mst@kernel.org> <87d06f57jd.fsf@linaro.org> MIME-Version: 1.0 In-Reply-To: <87d06f57jd.fsf@linaro.org> User-Agent: Mutt/1.13.4 (2020-02-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 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=205.139.110.61; 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 01:08:38 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_H2=-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: > > Michael S. Tsirkin writes: > > > On Thu, Jun 04, 2020 at 12:49:17PM +0100, Alex Bennée wrote: > >> > >> Michael S. Tsirkin writes: > >> > >> > On Thu, Jun 04, 2020 at 12:13:23PM +0100, Alex Bennée 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 > >> >> > >> >> 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; > >> > > >> > I'm not sure what does this enum buy us as compared to bool. > >> > >> The only real point of the enum is to give a little more detailed > >> information to the trace point to expose why a section wasn't included. > >> In a previous iteration I just had the tracepoint at the bottom before a > >> return true where all other legs had returned false. We could switch to > >> just having the tracepoint hit for explicit inclusions? > > > > I didn't notice. Yes, ok more tracepoints IMHO. > > I can simplify to two: > > trace_vhost_section(mr->name) > trace_vhost_reject_section(mr->name, int reason) > > Not sure if it's worth defining a enum outside just for the purposes of > the trace though. Do we have the concept of per-trace event enum codes? If you want a 'reason' for the trace, then why not just make const char *result Dave > >> > Also why force OK to 0? > >> > >> Personal preference where 0 indicates success and !0 indicates failure > >> of various kinds. Again we can drop if we don't want the information in > >> the tracepoint. > > > > So in that case we need to set all values so people can decode them > > from the trace. But I think it's best to just have more trace points > > or drop it from the trace. > > > >> > And I prefer an explicit "else result = NOT_RAM" below > >> > instead of initializing it here. > >> > >> Ok. > >> > >> > > >> >> + > >> >> + 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); > >> >> + } > >> > > >> > So DIRTY_MEMORY_CODE is only set by TCG right? Thus I'm guessing > >> > we can just allow this unconditionally. > >> > >> Which actually makes the test: > >> > >> if (dirty_mask & DIRTY_MEMORY_VGA) { > >> .. fail .. > >> } > >> > >> which is more in line with the comment although wouldn't fail if we > >> added additional DIRTY_MEMORY flags. This leads to the question what > >> exactly is it about DIRTY tracking that vhost doesn't like. > > > > vhost does not know how to track writes to specific regions. It can either > > track all writes to memory (which slows it down quite a bit) > > or no writes. > > So can vhost interfere with dirty tracking itself in the kernel by > trapping the writes? I guess there is no way this can happen with > vhost-user? > > (I wonder what would happen if a vhost-user daemon did an mprotect() on > RAM from it's shared view?) > > > It never actually *needs* to write to VGA, > > so we do a hack and just skip these and then if that's the > > only thing we need to track then we don't need to enable > > its dirty tracking. > > > > I don't really know what is DIRTY_MEMORY_CODE and when it's set. > > We use it softmmu do any pages that have code in them always force the > slow-path into cputlb for writes to those pages. This allows us to > detect self-modifying code. The kernel would never get involved but I > don't think vhost and TCG is compatible anyway. I'm only really > interested in vhost-user and it's interaction with TCG. > > I'll spin a v2 now. > > -- > Alex Bennée > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK