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Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , =?UTF-8?Q?Mika_Penttil=C3=A4?= , Francois Dugast References: <20251001065707.920170-1-balbirs@nvidia.com> <20251008201740.d9507f4807a73058d4da23a8@linux-foundation.org> <20251111154326.bc48466a6962fbbffd8ebdd0@linux-foundation.org> <7a0f2704-80b5-4cbd-8f3b-ac03692eefd3@nvidia.com> Content-Language: en-US From: Balbir Singh In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-ClientProxiedBy: BY3PR05CA0013.namprd05.prod.outlook.com (2603:10b6:a03:254::18) To PH8PR12MB7277.namprd12.prod.outlook.com (2603:10b6:510:223::13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR12MB7277:EE_|SA0PR12MB4352:EE_ X-MS-Office365-Filtering-Correlation-Id: 28aaccfe-38f1-4972-b65f-08de27df9e18 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|10070799003|1800799024|7416014|376014|366016|7053199007; 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The implementation enables >>>>>>> efficient migration of large folios between system memory and >>>>>>> device-private memory >>>>>> >>>>>> Lots of chatter for the v6 series, but none for v7. I hope that's a >>>>>> good sign. >>>>>> >>>>> >>>>> I hope so too, I've tried to address the comments in v6. >>>>> >>>> >>>> Circling back to this series, we will itegrate and test this version. >>> >>> How'd it go? >>> > > My apologies for the delay—I got distracted by other tasks in Xe (my > driver) and was out for a bit. Unfortunately, this series breaks > something in the existing core MM code for the Xe SVM implementation. I > have an extensive test case that hammers on SVM, which fully passes > prior to applying this series, but fails randomly with the series > applied (to drm-tip-rc6) due to the below kernel lockup. > > I've tried to trace where the migration PTE gets installed but not > removed or isolate a test case which causes this failure but no luck so > far. I'll keep digging as I have time. > > Beyond that, if I enable Xe SVM + THP, it seems to mostly work (though > the same issue as above eventually occurs), but I do need two additional > core MM patches—one is new code required for Xe, and the other could be > considered a bug fix. Those patches can included when Xe merges SVM THP > support but we need at least not break Xe SVM before this series merges. > > Stack trace: > > INFO: task kworker/u65:2:1642 blocked for more than 30 > seconds. > [ 212.624286] Tainted: G S W 6.18.0-rc6-xe+ #1719 > [ 212.630561] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" > disables this message. > [ 212.638285] task:kworker/u65:2 state:D stack:0 pid:1642 > tgid:1642 ppid:2 task_flags:0x4208060 flags:0x00080000 > [ 212.638288] Workqueue: xe_page_fault_work_queue > xe_pagefault_queue_work [xe] > [ 212.638323] Call Trace: > [ 212.638324] > [ 212.638325] __schedule+0x4b0/0x990 > [ 212.638330] schedule+0x22/0xd0 > [ 212.638331] io_schedule+0x41/0x60 > [ 212.638333] migration_entry_wait_on_locked+0x1d8/0x2d0 > [ 212.638336] ? __pfx_wake_page_function+0x10/0x10 > [ 212.638339] migration_entry_wait+0xd2/0xe0 > [ 212.638341] hmm_vma_walk_pmd+0x7c9/0x8d0 > [ 212.638343] walk_pgd_range+0x51d/0xa40 > [ 212.638345] __walk_page_range+0x75/0x1e0 > [ 212.638347] walk_page_range_mm+0x138/0x1f0 > [ 212.638349] hmm_range_fault+0x59/0xa0 > [ 212.638351] drm_gpusvm_get_pages+0x194/0x7b0 [drm_gpusvm_helper] > [ 212.638354] drm_gpusvm_range_get_pages+0x2d/0x40 [drm_gpusvm_helper] > [ 212.638355] __xe_svm_handle_pagefault+0x259/0x900 [xe] > [ 212.638375] ? update_load_avg+0x7f/0x6c0 > [ 212.638377] ? update_curr+0x13d/0x170 > [ 212.638379] xe_svm_handle_pagefault+0x37/0x90 [xe] > [ 212.638396] xe_pagefault_queue_work+0x2da/0x3c0 [xe] > [ 212.638420] process_one_work+0x16e/0x2e0 > [ 212.638422] worker_thread+0x284/0x410 > [ 212.638423] ? __pfx_worker_thread+0x10/0x10 > [ 212.638425] kthread+0xec/0x210 > [ 212.638427] ? __pfx_kthread+0x10/0x10 > [ 212.638428] ? __pfx_kthread+0x10/0x10 > [ 212.638430] ret_from_fork+0xbd/0x100 > [ 212.638433] ? __pfx_kthread+0x10/0x10 > [ 212.638434] ret_from_fork_asm+0x1a/0x30 > [ 212.638436] > Hi, Matt Thanks for the report, two questions 1. Are you using mm/mm-unstable, we've got some fixes in there (including fixes to remove_migration_pmd()) - Generally a left behind migration entry is a symptom of a failed migration that did not clean up after itself. 2. The stack trace is from hmm_range_fault(), not something that this code touches. The stack trace shows your code is seeing a migration entry and waiting on it. Can you please provide a reproducer for the issue? In the form of a test in hmm-tests.c Have you been able to bisect the issue? Balbir > Matt > >>> Balbir, what's the status here? It's been a month and this series >>> still has a "needs a new version" feeling to it. If so, very soon >>> please. >>> >> >> I don't think this needs a new revision, I've been testing frequently >> at my end to see if I can catch any regressions. I have a patch update for >> mm-migrate_device-add-thp-splitting-during-migration.patch, it can be applied >> on top or I can send a new version of the patch. I was waiting >> on any feedback before I sent the patch out, but I'll do it now. >> >>> TODOs which I have noted are >>> >>> https://lkml.kernel.org/r/aOePfeoDuRW+prFq@lstrano-desk.jf.intel.com >> >> This was a clarification on the HMM patch mentioned in the changelog >> >>> https://lkml.kernel.org/r/CABzRoyZZ8QLF5PSeDCVxgcnQmF9kFQ3RZdNq0Deik3o9OrK+BQ@mail.gmail.com >> >> That's a minor comment on not using a temporary declaration, I don't think we need it, let me know if you feel strongly >> >>> https://lkml.kernel.org/r/D2A4B724-E5EF-46D3-9D3F-EBAD9B22371E@nvidia.com >> >> I have a patch for this, which I posted, I can do an update and resend it if required (the one mentioned above) >> >>> https://lkml.kernel.org/r/62073ca1-5bb6-49e8-b8d4-447c5e0e582e@ >>> >> >> I can't seem to open this >> >>> plus a general re-read of the >>> mm-migrate_device-add-thp-splitting-during-migration.patch review >>> discussion. >>> >> That's the patch I have >> >> Thanks for following up >> Balbir