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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 452EDC433E0 for ; Mon, 11 Jan 2021 15:30:41 +0000 (UTC) Received: from lists.xenproject.org (lists.xenproject.org [192.237.175.120]) (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 BD9BB229CA for ; Mon, 11 Jan 2021 15:30:40 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BD9BB229CA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.64981.114966 (Exim 4.92) (envelope-from ) id 1kyz9M-0005Hc-NV; Mon, 11 Jan 2021 15:30:32 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 64981.114966; Mon, 11 Jan 2021 15:30:32 +0000 Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kyz9M-0005HU-KK; Mon, 11 Jan 2021 15:30:32 +0000 Received: by outflank-mailman (input) for mailman id 64981; Mon, 11 Jan 2021 15:30:32 +0000 Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kyz9L-0005HJ-UH for xen-devel@lists.xenproject.org; Mon, 11 Jan 2021 15:30:31 +0000 Received: from us-smtp-delivery-124.mimecast.com (unknown [216.205.24.124]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTP id 51d378b6-c9eb-43f1-904d-f3d14478c401; Mon, 11 Jan 2021 15:30:31 +0000 (UTC) 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-447-rKuPxOR8OTWhPxZvh-4K4Q-1; Mon, 11 Jan 2021 10:30:27 -0500 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 A2CF0107ACF8; Mon, 11 Jan 2021 15:30:25 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-112-114.ams2.redhat.com [10.36.112.114]) by smtp.corp.redhat.com (Postfix) with ESMTP id B476E5C1BB; Mon, 11 Jan 2021 15:30:23 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: 51d378b6-c9eb-43f1-904d-f3d14478c401 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610379031; 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=kv834PrhhD0okv0b+tQcDOD1Tlxp1VLNMhbsgSxeJiY=; b=PHWRPEtz/tG6OFox50Yy7IKKjo1H7bwzyN5tviIoVlWFZUvSIWjeL5gM79mLgmG+9V2UBH /fJtR05mdd1bx/MFI9HZIYac5p1WiHb1aPnn78DDFYSE/cdrOBA1So1UKbDsZNFBYnW7X1 Ta+uhXdvHy4NSoG8j73VtNS3WZIn6KA= X-MC-Unique: rKuPxOR8OTWhPxZvh-4K4Q-1 Subject: Re: [PATCH] hvmloader: pass PCI MMIO layout to OVMF as an info table To: Jan Beulich Cc: andrew.cooper3@citrix.com, roger.pau@citrix.com, wl@xen.org, iwj@xenproject.org, anthony.perard@citrix.com, xen-devel@lists.xenproject.org, Igor Druzhinin References: <1610340812-24397-1-git-send-email-igor.druzhinin@citrix.com> <20b1fe43-370b-9afc-6938-379480908578@redhat.com> From: Laszlo Ersek Message-ID: <398ae5fe-577c-4c91-2515-89fd5ab0bf99@redhat.com> Date: Mon, 11 Jan 2021 16:30:22 +0100 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=lersek@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 01/11/21 16:21, Jan Beulich wrote: > On 11.01.2021 15:49, Laszlo Ersek wrote: >> On 01/11/21 15:00, Igor Druzhinin wrote: >>> On 11/01/2021 09:27, Jan Beulich wrote: >>>> On 11.01.2021 05:53, Igor Druzhinin wrote: >>>>> We faced a problem with passing through a PCI device with 64GB BAR to >>>>> UEFI guest. The BAR is expectedly programmed into 64-bit PCI aperture at >>>>> 64G address which pushes physical address space to 37 bits. OVMF uses >>>>> address width early in PEI phase to make DXE identity pages covering >>>>> the whole addressable space so it needs to know the last address it needs >>>>> to cover but at the same time not overdo the mappings. >>>>> >>>>> As there is seemingly no other way to pass or get this information in >>>>> OVMF at this early phase (ACPI is not yet available, PCI is not yet enumerated, >>>>> xenstore is not yet initialized) - extend the info structure with a new >>>>> table. Since the structure was initially created to be extendable - >>>>> the change is backward compatible. >>>> >>>> How does UEFI handle the same situation on baremetal? I'd guess it is >>>> in even more trouble there, as it couldn't even read addresses from >>>> BARs, but would first need to assign them (or at least calculate >>>> their intended positions). >>> >>> Maybe Laszlo or Anthony could answer this question quickly while I'm investigating? >> >> On the bare metal, the phys address width of the processor is known. > > From CPUID I suppose. > >> OVMF does the whole calculation in reverse because there's no way for it >> to know the physical address width of the physical (= host) CPU. >> "Overdoing" the mappings doesn't only waste resources, it breaks hard >> with EPT -- access to a GPA that is inexpressible with the phys address >> width of the host CPU (= not mappable successfully with the nested page >> tables) will behave super bad. I don't recall the exact symptoms, but it >> prevents booting the guest OS. >> >> This is why the most conservative 36-bit width is assumed by default. > > IOW you don't trust virtualized CPUID output? That's correct; it's not trustworthy / reliable. One of the discussions (of the many) is here: https://lists.gnu.org/archive/html/qemu-devel/2020-06/msg04716.html Thanks Laszlo