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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 3E74CC433DF for ; Tue, 16 Jun 2020 16:59:03 +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 0BAE5208E4 for ; Tue, 16 Jun 2020 16:59:03 +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="AFAJ8fgN" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0BAE5208E4 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]:44494 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jlEvO-0003Lf-97 for qemu-devel@archiver.kernel.org; Tue, 16 Jun 2020 12:59:02 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41802) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jlEuO-0002Xc-7O for qemu-devel@nongnu.org; Tue, 16 Jun 2020 12:58:00 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:20975 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 1jlEuM-0004xq-9w for qemu-devel@nongnu.org; Tue, 16 Jun 2020 12:57:59 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1592326677; 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: in-reply-to:in-reply-to:references:references; bh=o1PsF6as5HbiO3n5zellw69hKG1kjmWUroALlSXOkhs=; b=AFAJ8fgNn6FjBfwMDf0kydG4fWyXS1nqBtf3xk2E6fzQyiy1RmL+yXqxlNxwjLisO3o/8S FKTaCeCkGSrMxga1nBNuAiqpfPlIzzGckhJAbzvZ1HWwyEg7zoQwKwDyQAzT3Pj/YXe9AH f1w25uYdBeen3w1Em/dQbM3+qyAoh6E= 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-290-5A3I7R-zO1Kk-BJpFaDd1Q-1; Tue, 16 Jun 2020 12:57:55 -0400 X-MC-Unique: 5A3I7R-zO1Kk-BJpFaDd1Q-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 628D68064D8; Tue, 16 Jun 2020 16:57:54 +0000 (UTC) Received: from work-vm (ovpn-112-42.ams2.redhat.com [10.36.112.42]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8DF281C4; Tue, 16 Jun 2020 16:57:49 +0000 (UTC) Date: Tue, 16 Jun 2020 17:57:46 +0100 From: "Dr. David Alan Gilbert" To: Gerd Hoffmann Subject: Re: ovmf / PCI passthrough impaired due to very limiting PCI64 aperture Message-ID: <20200616165746.GH2788@work-vm> References: <99779e9c-f05f-501b-b4be-ff719f140a88@canonical.com> <20200616165043.24y2cp53axk7uggy@sirius.home.kraxel.org> MIME-Version: 1.0 In-Reply-To: <20200616165043.24y2cp53axk7uggy@sirius.home.kraxel.org> User-Agent: Mutt/1.14.0 (2020-05-02) 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=us-ascii 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 = 2020/06/16 02:01:17 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, 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_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-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: pedro.principeza@canonical.com, ehabkost@redhat.com, dann.frazier@canonical.com, "Guilherme G. Piccoli" , qemu-devel@nongnu.org, christian.ehrhardt@canonical.com, lersek@redhat.com, fw@gpiccoli.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Gerd Hoffmann (kraxel@redhat.com) wrote: > Hi, > > > (a) We could rely in the guest physbits to calculate the PCI64 aperture. > > I'd love to do that. Move the 64-bit I/O window as high as possible and > use -- say -- 25% of the physical address space for it. > > Problem is we can't. > > > failure. Also, if the users are not setting the physbits in the guest, > > there must be a default (seems to be 40bit according to my experiments), > > seems to be a good idea to rely on that. > > Yes, 40 is the default, and it is used *even if the host supports less > than that*. Typical values I've seen for intel hardware are 36 and 39. > 39 is used even by recent hardware (not the xeons, but check out a > laptop or a nuc). > > > If guest physbits is 40, why to have OVMF limiting it to 36, right? > > Things will explode in case OVMF uses more physbits than the host > supports (host physbits limit applies to ept too). In other words: OVMF > can't trust the guest physbits, so it is conservative to be on the safe > side. > > If we can somehow make a *trustable* physbits value available to the > guest, then yes, we can go that route. But the guest physbits we have > today unfortunately don't cut it. In downstream RH qemu, we run with host-physbits as default; so it's reasonably trustworthy; of course that doesn't help you across a migration between hosts with different sizes (e.g. an E5 Xeon to an E3). Changing upstream to do the same would seem sensible to me, but it's not a foolproof config. Dave > take care, > Gerd > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK