Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Message-ID: <4468bea0-4813-a0e5-50bd-ce29f23d482e@oracle.com>
Date:   Fri, 11 Mar 2022 09:19:46 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0)
 Gecko/20100101 Thunderbird/91.6.2
Subject: Re: [PATCH v4 2/2] xen: delay xen_hvm_init_time_ops() if kdump is
 boot on vcpu>=32
Content-Language: en-US
To:     Dongli Zhang <dongli.zhang@oracle.com>,
        xen-devel@lists.xenproject.org, x86@kernel.org
Cc:     linux-kernel@vger.kernel.org, jgross@suse.com,
        sstabellini@kernel.org, tglx@linutronix.de, mingo@redhat.com,
        bp@alien8.de, dave.hansen@linux.intel.com, joe.jin@oracle.com
References: <20220302164032.14569-1-dongli.zhang@oracle.com>
 <20220302164032.14569-3-dongli.zhang@oracle.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
In-Reply-To: <20220302164032.14569-3-dongli.zhang@oracle.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?VkhHbUlTQVZNVlFMVTJ1NWlZUElCaFh3ZjJtd1RJYW01RXpZUnhHd0czRnAv?=
 =?utf-8?B?ZEVRU2tTUkJ4SE5abWdzd2lpTXhXNWZoTHA3QnhVemhzNEZkOGVuNUVjQnZn?=
 =?utf-8?B?aWhybC9xaHFsUFZPTlc2YUE2T3FOYzRwUkFsNjRMbHVFbUhqQjhybXM2M0Qr?=
 =?utf-8?B?T0JPZU1xYUNlMG9rNkJwZ3crTWIxTnJ4M2Zla2RjcXY0Q3ZoKzhibU1hNXhH?=
 =?utf-8?B?OVZaMjkwTlh1N1pTN3R1RXJsL1ppTVZ6VktMODE4TDFnVkFYYlREUk82MXQ4?=
 =?utf-8?B?NHRUSkpaZWFoQXZpWWx4eGlrMndQOThBMy9UQVFXdWlmdzVzVnRQRHovcElt?=
 =?utf-8?B?YXRBcWg3QXQrTXljVzRzL2pQUnFLVHV5cDlUT1FHYmdGViszRnA5MnNRcHBs?=
 =?utf-8?B?Z0loYVBuQ0dYMnBsYjVNa1J1MmJmUXN6K21VVm9mMGZVZUVtYUxJU1o0cElF?=
 =?utf-8?B?S0U3N2NJK2NUN0pSYTNCRVFMUXlvcTVxWmI4VHl6Nlc4VG9uUlRzVTgzSkFq?=
 =?utf-8?B?SkgzUk44Rjh3czNPUXlBeW5sSS91VkJzTm95NWZDUVJWRzJzczlTd3I0dERR?=
 =?utf-8?B?emhtVWcwRjU3bUJRWW5ySE9TTEdlRlA3blNHV1FyeE5rWHkwUm9zakZIN3o5?=
 =?utf-8?B?dm1yT1p5V21udUxDRmdNdlRPajVSdWVzb0tNSlU3eENNWFViRXNGam5RbzNB?=
 =?utf-8?B?MkJLNEk2dm9qWmVOSTBrcXB0SGZrTFdKS0JyQ3ZCOTVmdVRIOUVKdGxpM1RD?=
 =?utf-8?B?WVRpdG15Qm1KNFRMVGN3N3FSV2thdDVUMXYrNHhjUndVcUpLeUtLZ3daZDlq?=
 =?utf-8?B?QkY5cmZsSURqKzEwc21OQkduLzlnenBWd1MrVlpSbzdEc3N5TnFXdVZ4aXhk?=
 =?utf-8?B?Uys5WTlpZ1hNTzRzVTR1YkNUdi9FcGYwSUszSkpjL3BsMm4zaDkxd0w0eXpn?=
 =?utf-8?B?d2VVeDhIcit6bW40eXIzNkNIa3JtMEQ0WW5KTko0cWlpWUtJNVFpM2hmK1Jm?=
 =?utf-8?B?VWdHVzFocGowY0ZhOGVBR3p5OTQ1MGlHZm9TZ09iY21xRFBHcy9nSStIOURM?=
 =?utf-8?B?VnpxbUVrVytFSnFsNkJWUWg5YXJ2ZHdZcWpzek83U0xKVC82NnNuVUFnU21i?=
 =?utf-8?B?TmllWWVYWWVpLzZlQVByWVBzN284cE5mTm9USHpLRXVrWFZiVDA5azg2a3Zs?=
 =?utf-8?B?OXZDV25XQkI5a2FIcHFFT09DZ3ZwTEVIMDF6RVpNY3dVSkpOWUVNQjQvTmRi?=
 =?utf-8?B?NGxteDZYUGVVaVNoRGx1UldBUHU3VFRhVlRIMG5xYmFMSlBtS3pOa3B3cS9i?=
 =?utf-8?B?b3A1NTFVRExGN1c1WSttdnZISTliak1Zc2NhdkFkczhTaCtKcEFIS01lNlFI?=
 =?utf-8?B?Q3VYSHlRMHdaL2dZWnpSR1Q0SXdlZTl3OGp1cWNLeWdiQkpCV3JJcU1aZGlz?=
 =?utf-8?B?OXkxYWFROVEyZG9tWW04cGFiT0xjaWcwaFpkT0Z0SHFPWWN2VFhlWEZRTmpQ?=
 =?utf-8?B?dFFMaXQxU1c3WEZ1YVpHTHlvb2RaZ0E0N3UrWTBOZmRrNUU2VlExNjZvTnFX?=
 =?utf-8?B?bURzZ2Q2K3F2WUljbGdwaS9Dd3owL1hTK1NDUmtaS0ZqMk5jOFdjcjBsSlZX?=
 =?utf-8?B?SzFYSlBQWVN2cCtUQTIyOXYwNzc5V1NtWEVuZDF1QjUrK2dxbTBodzFaYUlL?=
 =?utf-8?B?ZnNCNmRDb0orQWZLUjJRUDBjRmpTb1JPVGJKQjRtd2NIVGl3RU85eEYwemNu?=
 =?utf-8?B?WnZkb3ZKKzg5US9obVJQYzN1TXdsOHZua3FUcklKcW10dnR1ZzFiR01hMWFp?=
 =?utf-8?B?Y1RBVjdUU0t5LzNIeGlSeDhqTWs0c0FnVXVBUnd5S05HeG9TQW5oWTlub2Zo?=
 =?utf-8?B?UzVKTW9HZW1RbWIxSWtoYzhHbmYvaXhtb1VpbDJvRVpBWUtFVzR0TXRWbjFU?=
 =?utf-8?B?UjVSdVExOE9tRFlaajdZalR1N0N1cnI2alZodkJHVkVOQWRoaVdrZ2dIbEly?=
 =?utf-8?B?K1pnUUVaV04xOUN1cTZHdEI5Z3FnRTE1MUREZmt5MkI4YXpCUHpkc21YQU00?=
 =?utf-8?B?NG5TNE9NU29NOHo2UHJsOW93YlBOMXdobE5Ud2N5T2liZ0VTY3lDWjVRN2FT?=
 =?utf-8?B?bmErTHFKVUdaQkU3dUZEczBGZmtaWE1uRVM1TXdPN2FMUkxJRWgyMXg5L3hO?=
 =?utf-8?B?eHVpSy9TUGVuR0FnR1RSSmsrYXNHREw3TGtFMmIyd3VIWjhNWDI4NkpwOUp1?=
 =?utf-8?Q?GcucaNYV4XrnvENsjfB2zxs05ewZJ1VRllojvpLbG0=3D?=
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: b5fb1a8f-d6e0-48c8-3e0d-08da036a3a00
X-MS-Exchange-CrossTenant-AuthSource: BLAPR10MB5009.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 11 Mar 2022 14:20:00.2107
 (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: DuG6uQMihY5O8pwaI6jNOQov8Fam9heglhq8T9fFeA0w0v1D4G4Dtj0+jrEkU3AV1uCSacyqNoBiD5hDJw8eZdzXA/BguLN4NDnqb264Y7M=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR10MB2901
X-Proofpoint-Virus-Version: vendor=nai engine=6300 definitions=10282 signatures=692556
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 malwarescore=0 mlxscore=0
 suspectscore=0 bulkscore=0 mlxlogscore=999 adultscore=0 spamscore=0
 phishscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2202240000 definitions=main-2203110070
X-Proofpoint-ORIG-GUID: r-PoXcf__L-nhKstcdDA2yG-XqCcJhZy
X-Proofpoint-GUID: r-PoXcf__L-nhKstcdDA2yG-XqCcJhZy
X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED,
	DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,
	MAILING_LIST_MULTI,NICE_REPLY_A,RDNS_NONE,SPF_HELO_NONE,
	T_SCC_BODY_TEXT_LINE autolearn=no 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 3/2/22 11:40 AM, Dongli Zhang wrote:
> The sched_clock() can be used very early since commit 857baa87b642
> ("sched/clock: Enable sched clock early"). In addition, with commit
> 38669ba205d1 ("x86/xen/time: Output xen sched_clock time from 0"), kdump
> kernel in Xen HVM guest may panic at very early stage when accessing
> &__this_cpu_read(xen_vcpu)->time as in below:
>
> setup_arch()
>   -> init_hypervisor_platform()
>       -> x86_init.hyper.init_platform = xen_hvm_guest_init()
>           -> xen_hvm_init_time_ops()
>               -> xen_clocksource_read()
>                   -> src = &__this_cpu_read(xen_vcpu)->time;
>
> This is because Xen HVM supports at most MAX_VIRT_CPUS=32 'vcpu_info'
> embedded inside 'shared_info' during early stage until xen_vcpu_setup() is
> used to allocate/relocate 'vcpu_info' for boot cpu at arbitrary address.
>
> However, when Xen HVM guest panic on vcpu >= 32, since
> xen_vcpu_info_reset(0) would set per_cpu(xen_vcpu, cpu) = NULL when
> vcpu >= 32, xen_clocksource_read() on vcpu >= 32 would panic.
>
> This patch calls xen_hvm_init_time_ops() again later in
> xen_hvm_smp_prepare_boot_cpu() after the 'vcpu_info' for boot vcpu is
> registered when the boot vcpu is >= 32.
>
> This issue can be reproduced on purpose via below command at the guest
> side when kdump/kexec is enabled:
>
> "taskset -c 33 echo c > /proc/sysrq-trigger"
>
> The bugfix for PVM is not implemented due to the lack of testing
> environment.
>
> Cc: Joe Jin <joe.jin@oracle.com>
> Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>


Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>


Applied to for-linus-5.18 (with return path adjusted)