From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:48408) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hEYAC-0003yV-5H for qemu-devel@nongnu.org; Thu, 11 Apr 2019 07:46:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hEYAA-0003jj-AC for qemu-devel@nongnu.org; Thu, 11 Apr 2019 07:46:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42748) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hEYA8-0003iU-Cq for qemu-devel@nongnu.org; Thu, 11 Apr 2019 07:46:37 -0400 Date: Thu, 11 Apr 2019 13:46:27 +0200 From: Igor Mammedov Message-ID: <20190411134627.15d7c340@redhat.com> In-Reply-To: <20190411013211.GA8515@richard> References: <1554822037-329838-1-git-send-email-imammedo@redhat.com> <20190410142756.GA3136@richard> <20190410170150.1c447b12@redhat.com> <20190411013211.GA8515@richard> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH for-4.1] q35: acpi: do not create dummy MCFG table List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wei Yang Cc: qemu-devel@nongnu.org, mst@redhat.com, marcel.apfelbaum@gmail.com, ehabkost@redhat.com On Thu, 11 Apr 2019 09:32:11 +0800 Wei Yang wrote: > On Wed, Apr 10, 2019 at 05:01:50PM +0200, Igor Mammedov wrote: > >On Wed, 10 Apr 2019 22:27:56 +0800 > >Wei Yang wrote: > > > >[...] > >> >@@ -2411,19 +2410,7 @@ build_mcfg_q35(GArray *table_data, BIOSLinker *linker, AcpiMcfgInfo *info) > >> > mcfg->allocation[0].start_bus_number = 0; > >> > mcfg->allocation[0].end_bus_number = PCIE_MMCFG_BUS(info->mcfg_size - 1); > >> > > >> >- /* MCFG is used for ECAM which can be enabled or disabled by guest. > >> > >> I want to cnfirm what is "enabled or disabled by guest" here. > > > >Firmware theoretically during PCI initialization may disable ECAM support > >and that's when we do no need MCFG. In practice that's not happening > >(SeaBIOS or UEFI) but we in case there is out there a firmware that does > >disable ECAM we do not generate MCFG. > > > >Note: > >ACPI tables generated twice, 1st when QEMU starts and the second time > >when firmware accesses fwcfg to read blobs for the 1st time. > >The later happens after PCI subsystem was initialized by firmware. > >At that time we know if ECAM was enabled or not. > > > > That's much clear, thanks :-) > > So this is the guest BIOS instead of guest kernel who may disable/enable it. > > >> If we don't reserve mcfg and "guest" enable mcfg during running, the ACPI > >> table size changed. But the destination still has the original table size, > >> since destination "guest" keep sleep during this period. > >> > >> Now the migration would face table size difference > > > >with commit a1666142db we do not care as all the tables created on > >source will be migrated to destination as is overwriting whatever blobs > >destination created on startup. > > > >> and break migration? > >nope, > > > >to help you figure out why it works > >look at what following git commits did: > > git log c8d6f66ae7..a1666142db > >and pay attention to 'used_length' > > > > To be honest, this is what I feel confused in your previous reply. > > First I want to confirm both fields in RAMBlock affects the migration: > > * used_length > * max_length > > Both of them should be the same on both source/destination, otherwise the > migration would fail. well, it works fine for me. Where do you see max_length being used during migration? > Then I thought the migration would be broken if source/destination has > different knowledge about acpi table size. Because this will introduce > different value of used_length, even we have resizable MemoryRegion. > > The 1st time ACPI generation flow: > > acpi_add_rom_blob > rom_add_blob > rom_set_mr > memory_region_init_resizable_ram > qemu_ram_alloc_resizable > new_block->used_length = size > new_block->max_length = max_size > > The 2nd time ACPI generation flow: > > acpi_ram_update > memory_regioin_ram_resize > qemu_ram_resize > block->used_length = new_size > > The max_length is always the same, while used_length would be changed to the > actual table_blob size. > > In case source/destination has different knowledge about acpi table size, the > table_blob size(even after aligned) could be different. > > This is why I thought there is still some chance to break migration after > resizable MemoryRegion. > > Do I miss something? yes, you did, max_length does not influence migration stream. see what above mentioned commits and ram_load() -> "if (length != block->used_length)" do. 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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 C228AC10F13 for ; Thu, 11 Apr 2019 11:47:46 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 94D882133D for ; Thu, 11 Apr 2019 11:47:46 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 94D882133D 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 ([127.0.0.1]:47228 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hEYBF-0004Se-Pc for qemu-devel@archiver.kernel.org; Thu, 11 Apr 2019 07:47:45 -0400 Received: from eggs.gnu.org ([209.51.188.92]:48408) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1hEYAC-0003yV-5H for qemu-devel@nongnu.org; Thu, 11 Apr 2019 07:46:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hEYAA-0003jj-AC for qemu-devel@nongnu.org; Thu, 11 Apr 2019 07:46:40 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42748) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hEYA8-0003iU-Cq for qemu-devel@nongnu.org; Thu, 11 Apr 2019 07:46:37 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A935D3082DCE; Thu, 11 Apr 2019 11:46:34 +0000 (UTC) Received: from localhost (unknown [10.43.2.182]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8296A60BF7; Thu, 11 Apr 2019 11:46:31 +0000 (UTC) Date: Thu, 11 Apr 2019 13:46:27 +0200 From: Igor Mammedov To: Wei Yang Message-ID: <20190411134627.15d7c340@redhat.com> In-Reply-To: <20190411013211.GA8515@richard> References: <1554822037-329838-1-git-send-email-imammedo@redhat.com> <20190410142756.GA3136@richard> <20190410170150.1c447b12@redhat.com> <20190411013211.GA8515@richard> MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Thu, 11 Apr 2019 11:46:34 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH for-4.1] q35: acpi: do not create dummy MCFG table X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: ehabkost@redhat.com, qemu-devel@nongnu.org, mst@redhat.com Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Message-ID: <20190411114627.I2i-2CdqaudurUZHNMM5wgIgRV5_TWLTfaUmpRau9Y4@z> On Thu, 11 Apr 2019 09:32:11 +0800 Wei Yang wrote: > On Wed, Apr 10, 2019 at 05:01:50PM +0200, Igor Mammedov wrote: > >On Wed, 10 Apr 2019 22:27:56 +0800 > >Wei Yang wrote: > > > >[...] > >> >@@ -2411,19 +2410,7 @@ build_mcfg_q35(GArray *table_data, BIOSLinker *linker, AcpiMcfgInfo *info) > >> > mcfg->allocation[0].start_bus_number = 0; > >> > mcfg->allocation[0].end_bus_number = PCIE_MMCFG_BUS(info->mcfg_size - 1); > >> > > >> >- /* MCFG is used for ECAM which can be enabled or disabled by guest. > >> > >> I want to cnfirm what is "enabled or disabled by guest" here. > > > >Firmware theoretically during PCI initialization may disable ECAM support > >and that's when we do no need MCFG. In practice that's not happening > >(SeaBIOS or UEFI) but we in case there is out there a firmware that does > >disable ECAM we do not generate MCFG. > > > >Note: > >ACPI tables generated twice, 1st when QEMU starts and the second time > >when firmware accesses fwcfg to read blobs for the 1st time. > >The later happens after PCI subsystem was initialized by firmware. > >At that time we know if ECAM was enabled or not. > > > > That's much clear, thanks :-) > > So this is the guest BIOS instead of guest kernel who may disable/enable it. > > >> If we don't reserve mcfg and "guest" enable mcfg during running, the ACPI > >> table size changed. But the destination still has the original table size, > >> since destination "guest" keep sleep during this period. > >> > >> Now the migration would face table size difference > > > >with commit a1666142db we do not care as all the tables created on > >source will be migrated to destination as is overwriting whatever blobs > >destination created on startup. > > > >> and break migration? > >nope, > > > >to help you figure out why it works > >look at what following git commits did: > > git log c8d6f66ae7..a1666142db > >and pay attention to 'used_length' > > > > To be honest, this is what I feel confused in your previous reply. > > First I want to confirm both fields in RAMBlock affects the migration: > > * used_length > * max_length > > Both of them should be the same on both source/destination, otherwise the > migration would fail. well, it works fine for me. Where do you see max_length being used during migration? > Then I thought the migration would be broken if source/destination has > different knowledge about acpi table size. Because this will introduce > different value of used_length, even we have resizable MemoryRegion. > > The 1st time ACPI generation flow: > > acpi_add_rom_blob > rom_add_blob > rom_set_mr > memory_region_init_resizable_ram > qemu_ram_alloc_resizable > new_block->used_length = size > new_block->max_length = max_size > > The 2nd time ACPI generation flow: > > acpi_ram_update > memory_regioin_ram_resize > qemu_ram_resize > block->used_length = new_size > > The max_length is always the same, while used_length would be changed to the > actual table_blob size. > > In case source/destination has different knowledge about acpi table size, the > table_blob size(even after aligned) could be different. > > This is why I thought there is still some chance to break migration after > resizable MemoryRegion. > > Do I miss something? yes, you did, max_length does not influence migration stream. see what above mentioned commits and ram_load() -> "if (length != block->used_length)" do.