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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 C0DAFC433DF for ; Sat, 27 Jun 2020 07:37:53 +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 9488020B80 for ; Sat, 27 Jun 2020 07:37:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9488020B80 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:43054 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jp5PM-0006ZT-Qm for qemu-devel@archiver.kernel.org; Sat, 27 Jun 2020 03:37:52 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58096) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jp5OY-00068y-Jq for qemu-devel@nongnu.org; Sat, 27 Jun 2020 03:37:02 -0400 Received: from mga04.intel.com ([192.55.52.120]:53041) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jp5OU-00010Z-4e for qemu-devel@nongnu.org; Sat, 27 Jun 2020 03:37:02 -0400 IronPort-SDR: HCwgxxSKfcEyxweSCoNYkDk5QhynJvPyNrsWGVbuIPkV8cW6oovhOFQhmcPNVQQcp6MG3hMnAZ fIVIYMqpzmJQ== X-IronPort-AV: E=McAfee;i="6000,8403,9664"; a="143108764" X-IronPort-AV: E=Sophos;i="5.75,286,1589266800"; d="scan'208";a="143108764" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by fmsmga104.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Jun 2020 00:36:53 -0700 IronPort-SDR: qMs1dShKQZ1cXnOO/bX6zS/0jAh329FWqmoRLHoWx2uGZozZqh8ZmVEyZKD8EsvKI0HbT0ROtq w2HTnMy3vk7w== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.75,286,1589266800"; d="scan'208";a="480232312" Received: from joy-optiplex-7040.sh.intel.com (HELO joy-OptiPlex-7040) ([10.239.13.16]) by fmsmga005.fm.intel.com with ESMTP; 27 Jun 2020 00:36:50 -0700 Date: Sat, 27 Jun 2020 03:26:45 -0400 From: Yan Zhao To: Peter Xu Subject: Re: [RFC v2 1/1] memory: Delete assertion in memory_region_unregister_iommu_notifier Message-ID: <20200627072644.GC18338@joy-OptiPlex-7040> References: <20200626064122.9252-1-eperezma@redhat.com> <20200626064122.9252-2-eperezma@redhat.com> <20200626212917.GD175520@xz-x1> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20200626212917.GD175520@xz-x1> User-Agent: Mutt/1.9.4 (2018-02-28) Received-SPF: none client-ip=192.55.52.120; envelope-from=yan.y.zhao@linux.intel.com; helo=mga04.intel.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/27 03:36:54 X-ACL-Warn: Detected OS = FreeBSD 9.x or newer [fuzzy] X-Spam_score_int: -41 X-Spam_score: -4.2 X-Spam_bar: ---- X-Spam_report: (-4.2 / 5.0 requ) BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_NONE=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: , Reply-To: Yan Zhao Cc: Peter Maydell , Yan Zhao , Juan Quintela , Jason Wang , "Michael S. Tsirkin" , qemu-devel@nongnu.org, Eugenio =?iso-8859-1?Q?P=E9rez?= , Eric Auger , Paolo Bonzini Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Fri, Jun 26, 2020 at 05:29:17PM -0400, Peter Xu wrote: > Hi, Eugenio, > > (CCing Eric, Yan and Michael too) > On Fri, Jun 26, 2020 at 08:41:22AM +0200, Eugenio Pérez wrote: > > diff --git a/memory.c b/memory.c > > index 2f15a4b250..7f789710d2 100644 > > --- a/memory.c > > +++ b/memory.c > > @@ -1915,8 +1915,6 @@ void memory_region_notify_one(IOMMUNotifier *notifier, > > return; > > } > > > > - assert(entry->iova >= notifier->start && entry_end <= notifier->end); > > I can understand removing the assertion should solve the issue, however imho > the major issue is not about this single assertion but the whole addr_mask > issue behind with virtio... Yes, the background for this assertion is https://lists.gnu.org/archive/html/qemu-devel/2019-06/msg04218.html > > For normal IOTLB invalidations, we were trying our best to always make > IOMMUTLBEntry contain a valid addr_mask to be 2**N-1. E.g., that's what we're > doing with the loop in vtd_address_space_unmap(). > > But this is not the first time that we may want to break this assumption for > virtio so that we make the IOTLB a tuple of (start, len), then that len can be > not a address mask any more. That seems to be more efficient for things like > vhost because iotlbs there are not page based, so it'll be inefficient if we > always guarantee the addr_mask because it'll be quite a lot more roundtrips of > the same range of invalidation. Here we've encountered another issue of > triggering the assertion with virtio-net, but only with the old RHEL7 guest. > > I'm thinking whether we can make the IOTLB invalidation configurable by > specifying whether the backend of the notifier can handle arbitary address > range in some way. So we still have the guaranteed addr_masks by default > (since I still don't think totally break the addr_mask restriction is wise...), > however we can allow the special backends to take adavantage of using arbitary > (start, len) ranges for reasons like performance. > > To do that, a quick idea is to introduce a flag IOMMU_NOTIFIER_ARBITRARY_MASK > to IOMMUNotifierFlag, to declare that the iommu notifier (and its backend) can > take arbitrary address mask, then it can be any value and finally becomes a > length rather than an addr_mask. Then for every iommu notify() we can directly > deliver whatever we've got from the upper layer to this notifier. With the new > flag, vhost can do iommu_notifier_init() with UNMAP|ARBITRARY_MASK so it > declares this capability. Then no matter for device iotlb or normal iotlb, we > skip the complicated procedure to split a big range into small ranges that are > with strict addr_mask, but directly deliver the message to the iommu notifier. > E.g., we can skip the loop in vtd_address_space_unmap() if the notifier is with > ARBITRARY flag set. > > Then, the assert() is not accurate either, and may become something like: > > diff --git a/memory.c b/memory.c > index 2f15a4b250..99d0492509 100644 > --- a/memory.c > +++ b/memory.c > @@ -1906,6 +1906,7 @@ void memory_region_notify_one(IOMMUNotifier *notifier, > { > IOMMUNotifierFlag request_flags; > hwaddr entry_end = entry->iova + entry->addr_mask; > + IOMMUTLBEntry tmp = *entry; > > /* > * Skip the notification if the notification does not overlap > @@ -1915,7 +1916,13 @@ void memory_region_notify_one(IOMMUNotifier *notifier, > return; > } > > - assert(entry->iova >= notifier->start && entry_end <= notifier->end); > + if (notifier->notifier_flags & IOMMU_NOTIFIER_ARBITRARY_MASK) { > + tmp.iova = MAX(tmp.iova, notifier->start); > + tmp.addr_mask = MIN(tmp.addr_mask, notifier->end); NIT: tmp.addr_mask = MIN(entry_end, notifier->end) - tmp.iova; > + assert(tmp.iova <= tmp.addr_mask); no this assertion then. Thanks Yan > + } else { > + assert(entry->iova >= notifier->start && entry_end <= notifier->end); > + } > > if (entry->perm & IOMMU_RW) { > request_flags = IOMMU_NOTIFIER_MAP; > @@ -1924,7 +1931,7 @@ void memory_region_notify_one(IOMMUNotifier *notifier, > } > > if (notifier->notifier_flags & request_flags) { > - notifier->notify(notifier, entry); > + notifier->notify(notifier, &tmp); > } > } > > Then we can keep the assert() for e.g. vfio, however vhost can skip it and even > get some further performance boosts.. Does that make sense? > > Thanks, > > -- > Peter Xu > >