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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 AF8C8C433DB for ; Tue, 16 Feb 2021 18:36:07 +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 68AF164E2B for ; Tue, 16 Feb 2021 18:36:07 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 68AF164E2B 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]:38120 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lC5Cg-0002Ib-Kc for qemu-devel@archiver.kernel.org; Tue, 16 Feb 2021 13:36:06 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36278) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lC5BF-0000wN-W1 for qemu-devel@nongnu.org; Tue, 16 Feb 2021 13:34:38 -0500 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:32441) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1lC5BD-0008JH-Qe for qemu-devel@nongnu.org; Tue, 16 Feb 2021 13:34:37 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1613500475; 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=GYgJmUI5DjHOGNh22RNLQeeR1dia/9NiJ4Ft22QMOsQ=; b=VR/E4BzxqM+iHAEROQFfmw6cH4gJlFTjpQJLFhB+2KgspxU0HDcCv7SYaVX2zU+nJK6DKs S6Wb6G3FoPnhzxeIs3dRUJm1JKUXtb+yPzS4TPjpN6g41pXMAfcbbSsbIqS5YfT3SJMDrR uuK24qgNpRpxYGbS4Ln6xfMHWVpVbh0= 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-531-JvRxwiGEM96jngQEuoV2Kg-1; Tue, 16 Feb 2021 13:34:32 -0500 X-MC-Unique: JvRxwiGEM96jngQEuoV2Kg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6428010082F5; Tue, 16 Feb 2021 18:34:31 +0000 (UTC) Received: from omen.home.shazbot.org (ovpn-112-255.phx2.redhat.com [10.3.112.255]) by smtp.corp.redhat.com (Postfix) with ESMTP id E696C6F452; Tue, 16 Feb 2021 18:34:19 +0000 (UTC) Date: Tue, 16 Feb 2021 11:34:06 -0700 From: Alex Williamson To: David Hildenbrand Subject: Re: [PATCH v5 06/11] vfio: Sanity check maximum number of DMA mappings with RamDiscardMgr Message-ID: <20210216113406.470665a5@omen.home.shazbot.org> In-Reply-To: <20210121110540.33704-7-david@redhat.com> References: <20210121110540.33704-1-david@redhat.com> <20210121110540.33704-7-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=alex.williamson@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=alex.williamson@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_H3=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: , Cc: Pankaj Gupta , Wei Yang , "Michael S. Tsirkin" , Jonathan Cameron , qemu-devel@nongnu.org, Peter Xu , "Dr . David Alan Gilbert" , Auger Eric , teawater , Igor Mammedov , Paolo Bonzini , Marek Kedzierski Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Thu, 21 Jan 2021 12:05:35 +0100 David Hildenbrand wrote: > Although RamDiscardMgr can handle running into the maximum number of > DMA mappings by propagating errors when creating a DMA mapping, we want > to sanity check and warn the user early that there is a theoretical setup > issue and that virtio-mem might not be able to provide as much memory > towards a VM as desired. > > As suggested by Alex, let's use the number of KVM memory slots to guess > how many other mappings we might see over time. > > Cc: Paolo Bonzini > Cc: "Michael S. Tsirkin" > Cc: Alex Williamson > Cc: Dr. David Alan Gilbert > Cc: Igor Mammedov > Cc: Pankaj Gupta > Cc: Peter Xu > Cc: Auger Eric > Cc: Wei Yang > Cc: teawater > Cc: Marek Kedzierski > Signed-off-by: David Hildenbrand > --- > hw/vfio/common.c | 43 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 43 insertions(+) Acked-by: Alex Williamson > diff --git a/hw/vfio/common.c b/hw/vfio/common.c > index 78be813a53..166ec6ec62 100644 > --- a/hw/vfio/common.c > +++ b/hw/vfio/common.c > @@ -761,6 +761,49 @@ static void vfio_register_ram_discard_notifier(VFIOContainer *container, > vfio_ram_discard_notify_discard_all); > rdmc->register_listener(rdm, section->mr, &vrdl->listener); > QLIST_INSERT_HEAD(&container->vrdl_list, vrdl, next); > + > + /* > + * Sanity-check if we have a theoretically problematic setup where we could > + * exceed the maximum number of possible DMA mappings over time. We assume > + * that each mapped section in the same address space as a RamDiscardMgr > + * section consumes exactly one DMA mapping, with the exception of > + * RamDiscardMgr sections; i.e., we don't expect to have gIOMMU sections in > + * the same address space as RamDiscardMgr sections. > + * > + * We assume that each section in the address space consumes one memslot. > + * We take the number of KVM memory slots as a best guess for the maximum > + * number of sections in the address space we could have over time, > + * also consuming DMA mappings. > + */ > + if (container->dma_max_mappings) { > + unsigned int vrdl_count = 0, vrdl_mappings = 0, max_memslots = 512; > + > +#ifdef CONFIG_KVM > + if (kvm_enabled()) { > + max_memslots = kvm_get_max_memslots(); > + } > +#endif > + > + QLIST_FOREACH(vrdl, &container->vrdl_list, next) { > + hwaddr start, end; > + > + start = QEMU_ALIGN_DOWN(vrdl->offset_within_address_space, > + vrdl->granularity); > + end = ROUND_UP(vrdl->offset_within_address_space + vrdl->size, > + vrdl->granularity); > + vrdl_mappings += (end - start) / vrdl->granularity; > + vrdl_count++; > + } > + > + if (vrdl_mappings + max_memslots - vrdl_count > > + container->dma_max_mappings) { > + warn_report("%s: possibly running out of DMA mappings. E.g., try" > + " increasing the 'block-size' of virtio-mem devies." > + " Maximum possible DMA mappings: %d, Maximum possible" > + " memslots: %d", __func__, container->dma_max_mappings, > + max_memslots); > + } > + } > } > > static void vfio_unregister_ram_discard_listener(VFIOContainer *container,