Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <c83da0ea-8b1a-ffab-6968-acb2e488ff59@oracle.com>
Date:   Wed, 12 Oct 2022 11:23:37 -0500
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.3.1
Subject: Re: [PATCH v12 7/7] x86/crash: Add x86 crash hotplug support
Content-Language: en-US
To:     Sourabh Jain <sourabhjain@linux.ibm.com>,
        Borislav Petkov <bp@alien8.de>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com,
        tglx@linutronix.de, mingo@redhat.com, dave.hansen@linux.intel.com,
        hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        konrad.wilk@oracle.com, boris.ostrovsky@oracle.com
References: <20220909210509.6286-1-eric.devolder@oracle.com>
 <20220909210509.6286-8-eric.devolder@oracle.com>
 <Yx7XEcXZ8PwwQW95@nazgul.tnic>
 <cb343eef-46be-2d67-b93a-84c75be86325@oracle.com> <YzRxPAoN+XmOfJzV@zn.tnic>
 <fd08c13d-a917-4cd6-85ec-267e0fe74c41@oracle.com>
 <7d0697ee-d6e8-dad1-ca77-f2e8104b0b0f@linux.ibm.com>
 <915f05fd-dbbc-e012-e3d2-e40ca13d4728@oracle.com>
 <ba047d83-d2e7-761f-7777-b7194411a8dc@linux.ibm.com>
From:   Eric DeVolder <eric.devolder@oracle.com>
In-Reply-To: <ba047d83-d2e7-761f-7777-b7194411a8dc@linux.ibm.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?QUx0bkhGK20zZk4zbUR1QmFrK3RNUDY0RXZpR21TRGtSK25YMXJCMUIreVVu?=
 =?utf-8?B?cytvTHJJRXlObkZCRnpBZ1JWVFJjNGVtU1JOelhMMmNVVUVaVUhpcGtpS3Ix?=
 =?utf-8?B?ZGxNZlkrUTMvUkpaZ09SSm1rRTZMVzRiVWVTdU1jdjBaQk4xWTJ0V2lqc3hk?=
 =?utf-8?B?bjMzV3ZCVStXRHAzMmk0bThpYThvdUpRdTBVK2I5NGdabGxIYXJOenRTM1Uv?=
 =?utf-8?B?STdVMU80Njd2RmZlUjJBckJSekI0RUhNWFFaWTZaRlZ6S1Q0SENTU2c1YjBF?=
 =?utf-8?B?d0J4aWJmWFBhYzZDcXkyZUEyNXZ0dTEza0FSL3dQUzE4UUZlL3pVMVZNUmhj?=
 =?utf-8?B?SHo2Z2FkazdkSUNYeXpLVk9ZakFTSUs5akpFVi83WWd1SHNSUVMxV1o0QldJ?=
 =?utf-8?B?UjRQQVNUanJxUCtaaklORUwza2cwMHVIbGFqRDV5UE4ydkhJNkxWZ0Qrempz?=
 =?utf-8?B?MGN4R2Z4Z2QzeWlvRmJIVXdKdlZ4VFJHYWI5NXlETVp6VFlmSTdwRWhlbFhm?=
 =?utf-8?B?S0VqZXRtRE1oRTFXNGE0RGNkWHkvWmRWZExneDlqK2libkJOa2Z6T0hlY3d4?=
 =?utf-8?B?OHhwbk9Fc2RLWEsreEFLaXFvTDFEWXhkSnNhVGdqQ3VBTXB1V1hCaE9FRXdI?=
 =?utf-8?B?SktaR0ZsZGY1UVFRc3pIYmxPc0JUVVlSb0JUWW92bi9uT0dSTi8vMWNuSDhn?=
 =?utf-8?B?OGFQRkpMeE5mcEJ1OGJFMWlpbzJHb1ZJbk5JNTBqYmhoaUhUMVQ0YTR3d25Y?=
 =?utf-8?B?M1ZmRGNvSGp2Y2lOTHZGeXRqWFZZeXhzaUJ6NmU3QjB1U2wxSWRFTFdYc3lj?=
 =?utf-8?B?OENFMDVVNmhZYlhuV0F3VmNVTElZN2xaWHUrakRWTXpaZEMyaFJKSDViTjBQ?=
 =?utf-8?B?M1d5UmdiV0tNR0dQRko1aFQzSXZXZHdyaUtjRmgxT0FNU3dTSGNFYmZTMlpu?=
 =?utf-8?B?Tk9RQ0lwYmUrQjRCQ2o2eDBtdHlXK3NmSVFScFlQNDg2Q2VjS2JwbGRXS3RT?=
 =?utf-8?B?TkxuaEtkWVlnUFBKODUrZzFjbXVIc0wwRTkveitoZVUzakd0UkNhZ1JGazhE?=
 =?utf-8?B?UUlxbUdyb2IrNmR5cGNtdFpDMXFsRkw4ZWNjSDJsZC9jOTdHSUc1ZnQxNVQy?=
 =?utf-8?B?ckN4bG44dGhaOTkzSmZwY1IxUW93dDAxWFJpTmY4NnlMODFuSDR3RzdodGhs?=
 =?utf-8?B?L0JEb2p2b1NoV3h5cWs1cUh4L3ZycU9uVDVXdUl4UHp2d1dtLzVHWlRsL2la?=
 =?utf-8?B?ZHV0UThRUkptTTc0NzJLaDkyQ3M2Nmx3QXRiTWV0YWpkazN5MEIvZVo4bS9x?=
 =?utf-8?B?UEhKcnRRY2FqcWNyQksxMmYrWFUwV1ZTRU9KZm5Ra0FpM09CQUtoaUJLY1pM?=
 =?utf-8?B?NnhSYWVsTTNJdG1YZmRzQ25WYStBSGtwMVNzdE11Ym1VSmVTKzFEcmJmWjRW?=
 =?utf-8?B?QjdKMG5RZEk1STZLVnFnV3doYXhLbkhMRTJiNFFtb3dXZStmaG0wQTVFaUdS?=
 =?utf-8?B?STJmS3I1YXJNNmhqMDdySlNmRCtRc2dwbDlQMzZpdHFwNlVicTFERkpmNWpN?=
 =?utf-8?B?bUxnQWVDa0VXRzZKcmdacnBqUkkvNGhIS1dWUitWcmF0MTFjMUp4U2hEdkNp?=
 =?utf-8?B?Z3B1a3VOci9ZQTB1TU9HeUwvMi9CbWx1TUNTeHUyT0ZNQzJiaVZZU0V6OXhE?=
 =?utf-8?B?VkhQV0RzeUtZb2tpamRwU1ZsN2IyY285R0VuNWVkOE1EYlpDRVpPZ0VPQ01W?=
 =?utf-8?B?QlJpVU40c1huVmdMUHhxN2ZqdUhZdUVBak1jZEZoZ3JGTTFJemFPLy9QOS9V?=
 =?utf-8?B?SHFXaWpOSjNnaXViMEUzaHI1aEtqb1ZIUG5LZUdKRUdYdVhEYUFySUQ4cnMr?=
 =?utf-8?B?OUxtMy9tTG9FZTFCTWxhTmt0RHNuZDJlcXZYN3Y0UUJobS9hTk1mZUsvWmdO?=
 =?utf-8?B?V2tMQlNYNkRwM2F6L3VhZWxQQkJQRFR2VHZFdmtyU1dyV2wrVHZEY0ZVUk9D?=
 =?utf-8?B?S2hRR05TdzJ0ZU5CNDVoYzZvWmVGSVhsK3UvZnBiR2xNUnBkWC83SFV4VXZY?=
 =?utf-8?B?c1l5SVpwaStNMkdMM2dHejRCb2RIbmp4Q09WMTBHb1hNODlQT2l5MXJJRjhY?=
 =?utf-8?B?ZitOYUhoUzFMRFE5QkJoVDBYUFFmMnVBc0loeGZQbE95UFpDTnFmWmtCQkpN?=
 =?utf-8?Q?tJHQFYyRK+XoSxiX0EaCVN8=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: a55f5060-f898-463b-d28a-08daac6e21e5
X-MS-Exchange-CrossTenant-AuthSource: CO1PR10MB4531.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 12 Oct 2022 16:23:44.3951
 (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: Kw7ztLWwS08ZzGmM/XwuiehEoK0wc63wQzlEksidQiXA9edYrmkl5jPHrebkFbIFV6HCEkINgHojnlFiV+UXMbhUdKi0Dw61PTYL9Jd9efk=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: CH3PR10MB6835
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.545,FMLib:17.11.122.1
 definitions=2022-10-12_07,2022-10-12_01,2022-06-22_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 bulkscore=0 phishscore=0
 mlxlogscore=999 mlxscore=0 spamscore=0 adultscore=0 malwarescore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2209130000
 definitions=main-2210120107
X-Proofpoint-GUID: mgJd8uOwFaRqSesg-CVGAKhoXY7mJDYh
X-Proofpoint-ORIG-GUID: mgJd8uOwFaRqSesg-CVGAKhoXY7mJDYh
X-Spam-Status: No, score=-3.3 required=5.0 tests=BAYES_00,DKIM_SIGNED,
        DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,RCVD_IN_DNSWL_LOW,
        RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham
        autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


On 10/11/22 23:55, Sourabh Jain wrote:
> 
>>>>>> If kmap_local_page() works for all archs, then I'm happy to drop these
>>>>>> arch_ variants and use it directly.
>>>>>
>>>>> Yes, pls do.
>>>>
>>>> I'll check with Sourabh to see if PPC can work with kmap_local_page().
>>> I think kmap_local_page do support on  PowerPC. But can you explain why we need this
>>> function here, aren't the reserve memory already available to use?
>>
>> On x86, attempts to access the elfcorehdr without mapping it did not work (resulted
>> in a fault).
>>
>> Let me know if using kmap_local_page() in place of __va() in arch_map_crash_pages().
>> If it does, then I can eliminate arch_un/map_crash_pages() and use kmap_local_page()
>> directly.
> Hello Eric,
> 
> Atleast on ppc64 we have direct mapping available and hence just by doing page shift
> on physical address (__va) we can get valid virtual address on powerpc. In short we don't
> have to generate mapping again to access reserved region.
> 
> Regardless let's go with kdump_local_page API, it is supported on powerpc.
> 
> Thanks,
> Sourabh Jain

Ok, I will go that route.
Thanks!
eric