From patchwork Wed Jun 30 19:07:13 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Eric DeVolder X-Patchwork-Id: 12352755 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=-16.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,MSGID_FROM_MTA_HEADER,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT 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 27A9AC11F65 for ; Wed, 30 Jun 2021 19:16:19 +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 6F0D561449 for ; Wed, 30 Jun 2021 19:16:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6F0D561449 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=oracle.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:59566 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lyfh3-00031n-Di for qemu-devel@archiver.kernel.org; Wed, 30 Jun 2021 15:16:17 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:53392) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lyfZ6-0006vD-NS for qemu-devel@nongnu.org; Wed, 30 Jun 2021 15:08:04 -0400 Received: from mx0b-00069f02.pphosted.com ([205.220.177.32]:4604) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lyfZ2-0005kc-9d for qemu-devel@nongnu.org; Wed, 30 Jun 2021 15:08:04 -0400 Received: from pps.filterd (m0246631.ppops.net [127.0.0.1]) by mx0b-00069f02.pphosted.com (8.16.0.43/8.16.0.43) with SMTP id 15UJ6T05005964; Wed, 30 Jun 2021 19:07:58 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.com; h=from : to : cc : subject : date : message-id : in-reply-to : references : content-type : mime-version; s=corp-2020-01-29; bh=ggeqCo9toM/losbgAVSrqqlAcxFnvdTRMu+611m9pwI=; b=pNKaKbqtcsow6ZSr1/GN4LLHYhzWsopxS0g+ul1rpgTPX4kQXOle5kgHVnxacQnfxka1 kDFq9QJAZAoFkMvsNJk5NqFCP9mOJH7BxeZXP4Xp72TGxnIjbI1w6jTEFBMuyyjmWem0 LDAmSjbstvfs2DiKUCIDntBEzf/z5q9nZ4KO3p0mBWhQYFwWCwZjMsxmkWl1w34YZc9C 6+2usvQhVcYsB53WlZKPE42WcMYbChO1KNAtObrP4EWxeGYwTzLzMdI7F50Dl5nV+fG2 /JjELvtMjAjybPgl/nrqIVw0V9fgkr5wi5f2qinlbH9RMpHui4+ldNIssFxiT2ok0d8g bg== Received: from aserp3030.oracle.com (aserp3030.oracle.com [141.146.126.71]) by mx0b-00069f02.pphosted.com with ESMTP id 39gb2t26wx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 30 Jun 2021 19:07:57 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.42/8.16.0.42) with SMTP id 15UJ0CFH101369; Wed, 30 Jun 2021 19:07:57 GMT Received: from nam11-bn8-obe.outbound.protection.outlook.com (mail-bn8nam11lp2175.outbound.protection.outlook.com [104.47.58.175]) by aserp3030.oracle.com with ESMTP id 39dt9hqny5-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 30 Jun 2021 19:07:56 +0000 ARC-Seal: i=1; a=rsa-sha256; s=arcselector9901; d=microsoft.com; cv=none; b=T4oW0lLfN3tqef1dimZYs3I2lzdSXyWWX8+YPXeeJ3lIg7VTjVHgVPNuKRMdVyuGGqTvRDX9SG6bsC1Qgr5DpnBeaOV2hi4ORy5uq6GZRhHHxRrBguwLdPwQDrhBZy2Pc3etCaYGUbyyV+oFp3tsgy4CLzqORnjm0POd1myZ6BfiVW34Bri39I5FxPMOFDOD2R85CwaLNknGzWFCy9z6akDYM+mkyEb7wYdo52ua2gykyz1R48XtN42ya1+lYEWDkmj91S7auwM7RXD9YUgxSL9Z0dOGK9PxwajEEnH0ZWpDCirJ/CQEMOgRczVjNjCvCwvXM8/eIC/BebsMtO8iJA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector9901; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=ggeqCo9toM/losbgAVSrqqlAcxFnvdTRMu+611m9pwI=; b=UJPQPtj9I8oeiMi/iQAj6dFHdnsd5vYYUKE9EE8DLXGaKYV2XDLmineZBT0Zb3VXBFzda/zgjWCbNIaBjJWJPcbjQ59GMqsG6bgbWnhNFQ33QSqFfE0vRldLs/By1rutYdtr/7EOrYPN5KiPWqHbwVvsdOJz46LkFv4t9SwmP3oMFmIN6/3ol9CXgu5zapTdf3M69enSPWwqCKmHK3FmFBIJkMQiL50z9u/lOI2k0DVrEf5eOnMwt/uizZG98f27565tVR/MqPm+XVITaH1We5g6prA/w0EP4hq6ZPkERFLw5Yh1rfHatCQPCgn2jRWS0NYV3/VEu2vCincc+MSgDA== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=oracle.com; dmarc=pass action=none header.from=oracle.com; dkim=pass header.d=oracle.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=oracle.onmicrosoft.com; s=selector2-oracle-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=ggeqCo9toM/losbgAVSrqqlAcxFnvdTRMu+611m9pwI=; b=upDemyqk1JSKaw732bl24yZImIjpcSLK+oguIeo6PJfptXkSpzNJmcTR2zDcp1MNkCiwOTKoNNYBVSW+JOMapre+v1654HSKsQDbpGyGpkRSwnDaZyTxmuyraXQodrs1+nK3fyiPCDNFbsELLgZtme0C0ZBk303yOwKcCVhW5bY= Authentication-Results: nongnu.org; dkim=none (message not signed) header.d=none;nongnu.org; dmarc=none action=none header.from=oracle.com; Received: from CO1PR10MB4531.namprd10.prod.outlook.com (2603:10b6:303:6c::22) by CO6PR10MB5441.namprd10.prod.outlook.com (2603:10b6:5:35a::8) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4264.18; Wed, 30 Jun 2021 19:07:54 +0000 Received: from CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::a0af:e69c:6e81:b8fc]) by CO1PR10MB4531.namprd10.prod.outlook.com ([fe80::a0af:e69c:6e81:b8fc%7]) with mapi id 15.20.4287.023; Wed, 30 Jun 2021 19:07:54 +0000 From: Eric DeVolder To: qemu-devel@nongnu.org Subject: [PATCH v5 02/10] ACPI ERST: specification for ERST support Date: Wed, 30 Jun 2021 15:07:13 -0400 Message-Id: <1625080041-29010-3-git-send-email-eric.devolder@oracle.com> X-Mailer: git-send-email 1.8.3.1 In-Reply-To: <1625080041-29010-1-git-send-email-eric.devolder@oracle.com> References: <1625080041-29010-1-git-send-email-eric.devolder@oracle.com> X-Originating-IP: [138.3.201.23] X-ClientProxiedBy: BYAPR01CA0060.prod.exchangelabs.com (2603:10b6:a03:94::37) To CO1PR10MB4531.namprd10.prod.outlook.com (2603:10b6:303:6c::22) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from ban25x6uut23.us.oracle.com (138.3.201.23) by BYAPR01CA0060.prod.exchangelabs.com (2603:10b6:a03:94::37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4287.23 via Frontend Transport; Wed, 30 Jun 2021 19:07:53 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 076908a8-875d-4a38-5f5f-08d93bfa5d53 X-MS-TrafficTypeDiagnostic: CO6PR10MB5441: X-MS-Exchange-Transport-Forked: True X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:8882; X-MS-Exchange-SenderADCheck: 1 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: Ou0z9YuR8Iq5OHOJQ9JrjlP4XChto1al47aacj3zyp3UOiJHn+Uj41FTD4tjkbswlZDMchCoUq4eLJSVoT1g1XvH+5Gt52SCwadiCryEWO33nbK2o+21UYnjVfooUW0CJB138wwHNiY7biB9gXnFj/O+awYvDv4LK02NOw4VFixlUyEXibUHFcjWCn5CKyUtduIyWcRTECQUuyX59EcGivrBmGp6J4s/hLqrSvLA6CLrhP/GWKAS6Y34hpzsxTxWHZ8B1tOie0BdZEDnFfB8xgpO/0df324RTbegBl4+FgcAnEqgX3pZzp5ZiAMeQZC+2Wn63ou2YOtss8XzxQNkkQ7bHYNPPvlzZM5KbwuoDBqRX2w2TMG+Y7SUmTFY/Nc1iPyGsb/mBu/Ww3ePoRhPxfzafV28zFzUeCPBnsosSTwgPYS0duWm0pzCiT9hgLmNqEpKvB3bST9WV2Um+eO85U0+sMSKmd2Wj0GrG3n27Xmmi6sXBcxQ6lrGTvucpWbxTiLYyAOotfo3GD6IrZ6sfnnCiPgUCltFGr9th6tDSIdDDylZTFq2C9WyJ7re4oTIs3z8q5EGrhTnpM3ohmE3UonAfjE9Z2yEldMBwpFADkZ3xDfks3B8UvtxWpRmPMK5dkHMF3SCSRbULnOYocWxnLew8xDIw7f+GpyKyvLX+CKmL38OIHjFbP7sBlQGIiOvhhhB904colMSDNd0p3Zg+g== X-Forefront-Antispam-Report: CIP:255.255.255.255; CTRY:; LANG:en; SCL:1; SRV:; IPV:NLI; SFV:NSPM; H:CO1PR10MB4531.namprd10.prod.outlook.com; PTR:; CAT:NONE; SFS:(366004)(346002)(39860400002)(376002)(396003)(136003)(8936002)(107886003)(38350700002)(38100700002)(26005)(36756003)(186003)(8676002)(5660300002)(2616005)(956004)(16526019)(4326008)(86362001)(66946007)(7696005)(52116002)(316002)(66556008)(6666004)(45080400002)(66476007)(83380400001)(6916009)(478600001)(2906002)(6486002); DIR:OUT; SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: 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 X-OriginatorOrg: oracle.com X-MS-Exchange-CrossTenant-Network-Message-Id: 076908a8-875d-4a38-5f5f-08d93bfa5d53 X-MS-Exchange-CrossTenant-AuthSource: CO1PR10MB4531.namprd10.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Jun 2021 19:07:54.4518 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: AuLYPdXKf416qH9vxDc3Ah7HOpbUq15ztNK3y2cwVatXQ6hwV/mZ476vbCQ9KlcZn0q6eQbYCVnZ9sAXoKDy7ZqffI7/RudcL4EGx/MHW18= X-MS-Exchange-Transport-CrossTenantHeadersStamped: CO6PR10MB5441 X-Proofpoint-Virus-Version: vendor=nai engine=6200 definitions=10031 signatures=668682 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 adultscore=0 bulkscore=0 mlxlogscore=916 phishscore=0 spamscore=0 malwarescore=0 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2106300106 X-Proofpoint-GUID: gRvJ9D5FEw5qsVewCkvxF5uCdBtJZCoe X-Proofpoint-ORIG-GUID: gRvJ9D5FEw5qsVewCkvxF5uCdBtJZCoe Received-SPF: pass client-ip=205.220.177.32; envelope-from=eric.devolder@oracle.com; helo=mx0b-00069f02.pphosted.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, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, MSGID_FROM_MTA_HEADER=0.001, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H2=-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: ehabkost@redhat.com, mst@redhat.com, konrad.wilk@oracle.com, pbonzini@redhat.com, imammedo@redhat.com, boris.ostrovsky@oracle.com, rth@twiddle.net Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Information on the implementation of the ACPI ERST support. Signed-off-by: Eric DeVolder --- docs/specs/acpi_erst.txt | 152 +++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 152 insertions(+) create mode 100644 docs/specs/acpi_erst.txt diff --git a/docs/specs/acpi_erst.txt b/docs/specs/acpi_erst.txt new file mode 100644 index 0000000..79f8eb9 --- /dev/null +++ b/docs/specs/acpi_erst.txt @@ -0,0 +1,152 @@ +ACPI ERST DEVICE +================ + +The ACPI ERST device is utilized to support the ACPI Error Record +Serialization Table, ERST, functionality. The functionality is +designed for storing error records in persistent storage for +future reference/debugging. + +The ACPI specification[1], in Chapter "ACPI Platform Error Interfaces +(APEI)", and specifically subsection "Error Serialization", outlines +a method for storing error records into persistent storage. + +The format of error records is described in the UEFI specification[2], +in Appendix N "Common Platform Error Record". + +While the ACPI specification allows for an NVRAM "mode" (see +GET_ERROR_LOG_ADDRESS_RANGE_ATTRIBUTES) where non-volatile RAM is +directly exposed for direct access by the OS/guest, this implements +the non-NVRAM "mode". This non-NVRAM "mode" is what is implemented +by most BIOS (since flash memory requires programming operations +in order to update its contents). Furthermore, as of the time of this +writing, Linux does not support the non-NVRAM "mode". + + +Background/Motivation +--------------------- +Linux uses the persistent storage filesystem, pstore, to record +information (eg. dmesg tail) upon panics and shutdowns. Pstore is +independent of, and runs before, kdump. In certain scenarios (ie. +hosts/guests with root filesystems on NFS/iSCSI where networking +software and/or hardware fails), pstore may contain the only +information available for post-mortem debugging. + +Two common storage backends for the pstore filesystem are ACPI ERST +and UEFI. Most BIOS implement ACPI ERST. UEFI is not utilized in +all guests. With QEMU supporting ACPI ERST, it becomes a viable +pstore storage backend for virtual machines (as it is now for +bare metal machines). + +Enabling support for ACPI ERST facilitates a consistent method to +capture kernel panic information in a wide range of guests: from +resource-constrained microvms to very large guests, and in +particular, in direct-boot environments (which would lack UEFI +run-time services). + +Note that Microsoft Windows also utilizes the ACPI ERST for certain +crash information, if available. + + +Invocation +---------- + +To utilize ACPI ERST, a memory-backend-file object and acpi-erst +device must be created, for example: + + qemu ... + -object memory-backend-file,id=erstnvram,mem-path=acpi-erst.backing, + size=0x10000,share=on + -device acpi-erst,memdev=erstnvram + +For proper operation, the ACPI ERST device needs a memory-backend-file +object with the following parameters: + + - id: The id of the memory-backend-file object is used to associate + this memory with the acpi-erst device. + - size: The size of the ACPI ERST backing storage. This parameter is + required. + - mem-path: The location of the ACPI ERST backing storage file. This + parameter is also required. + - share: The share=on parameter is required so that updates to the + ERST back store are written to the file immediately as well. Without + it, updates the the backing file are unpredictable and may not + properly persist (eg. if qemu should crash). + +The ACPI ERST device is a simple PCI device, and requires this one +parameter: + + - memdev: Is the object id of the memory-backend-file. + + +PCI Interface +------------- + +The ERST device is a PCI device with two BARs, one for accessing +the programming registers, and the other for accessing the +record exchange buffer. + +BAR0 contains the programming interface consisting of just two +64-bit registers. The two registers are an ACTION (cmd) and a +VALUE (data). All ERST actions/operations/side effects happen +on the write to the ACTION, by design. Thus any data needed +by the action must be placed into VALUE prior to writing +ACTION. Reading the VALUE simply returns the register contents, +which can be updated by a previous ACTION. This behavior is +encoded in the ACPI ERST table generated by QEMU. + +BAR1 contains the record exchange buffer, and the size of this +buffer sets the maximum record size. This record exchange +buffer size is 8KiB. + +Backing File +------------ + +The ACPI ERST persistent storage is contained within a single backing +file. The size and location of the backing file is specified upon +QEMU startup of the ACPI ERST device. + +Records are stored in the backing file in a simple fashion. +The backing file is essentially divided into fixed size +"slots", ERST_RECORD_SIZE in length, with each "slot" +storing a single record. No attempt at optimizing storage +through compression, compaction, etc is attempted. +NOTE that any change to this value will make any pre- +existing backing files, not of the same ERST_RECORD_SIZE, +unusable to the guest. + +Below is an example layout of the backing store file. +The size of the file is a multiple of ERST_RECORD_SIZE, +and contains N number of "slots" to store records. The +example below shows two records (in CPER format) in the +backing file, while the remaining slots are empty/ +available. + + Slot Record + +--------------------------------------------+ + 0 | empty/available | + +--------------------------------------------+ + 1 | CPER | + +--------------------------------------------+ + 2 | CPER | + +--------------------------------------------+ + ... | | + +--------------------------------------------+ + N | empty/available | + +--------------------------------------------+ + <-------------- ERST_RECORD_SIZE ------------> + +Not all slots need to be occupied, and they need not be +occupied in a contiguous fashion. The ability to clear/erase +specific records allows for the formation of unoccupied +slots. + + +References +---------- + +[1] "Advanced Configuration and Power Interface Specification", + version 4.0, June 2009. + +[2] "Unified Extensible Firmware Interface Specification", + version 2.1, October 2008. +