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Mon, 21 Jul 2025 11:42:32 +0000 Date: Mon, 21 Jul 2025 13:42:01 +0200 From: Francois Dugast To: Balbir Singh CC: Matthew Brost , , , , Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , =?iso-8859-1?B?Suly9G1l?= Glisse , Shuah Khan , David Hildenbrand , "Barry Song" , Baolin Wang , "Ryan Roberts" , Matthew Wilcox , "Peter Xu" , Zi Yan , Kefeng Wang , Jane Chu , Alistair Popple , Donet Tom Subject: Re: [v1 resend 00/12] THP support for zone device page migration Message-ID: References: <20250703233511.2028395-1-balbirs@nvidia.com> <09c5ce76-f7c1-41c7-97e1-74448e6143f7@nvidia.com> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <09c5ce76-f7c1-41c7-97e1-74448e6143f7@nvidia.com> Organization: Intel Corporation X-ClientProxiedBy: LO6P123CA0043.GBRP123.PROD.OUTLOOK.COM (2603:10a6:600:2fe::17) To CY8PR11MB7828.namprd11.prod.outlook.com (2603:10b6:930:78::8) 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: CY8PR11MB7828:EE_|CO1PR11MB5027:EE_ X-MS-Office365-Filtering-Correlation-Id: 545121fe-70c4-4e77-22f5-08ddc84badd3 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|376014|7416014; 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I wanted to give > > some quick feedback: > > > > Are you seeing improvements with the patchset? > > > - You appear to have missed updating hmm_range_fault, specifically > > hmm_vma_handle_pmd, to check for device-private entries and populate the > > HMM PFNs accordingly. My colleague François has a fix for this if you're > > interested. > > > > Sure, please feel free to post them. Hi Balbir, It seems we are missing this special handling in in hmm_vma_walk_pmd(): diff --git a/mm/hmm.c b/mm/hmm.c index f2415b4b2cdd..449025f72b2f 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -355,6 +355,27 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, } if (!pmd_present(pmd)) { + swp_entry_t entry = pmd_to_swp_entry(pmd); + + /* + * Don't fault in device private pages owned by the caller, + * just report the PFNs. + */ + if (is_device_private_entry(entry) && + pfn_swap_entry_folio(entry)->pgmap->owner == + range->dev_private_owner) { + unsigned long cpu_flags = pmd_to_hmm_pfn_flags(range, pmd); + unsigned long pfn = swp_offset_pfn(entry); + unsigned long i; + + for (i = 0; addr < end; addr += PAGE_SIZE, i++, pfn++) { + hmm_pfns[i] &= HMM_PFN_INOUT_FLAGS; + hmm_pfns[i] |= pfn | cpu_flags; + } + + return 0; + } + if (hmm_range_need_fault(hmm_vma_walk, hmm_pfns, npages, 0)) return -EFAULT; return hmm_pfns_fill(start, end, range, HMM_PFN_ERROR); Francois > > > - I believe copy_huge_pmd also needs to be updated to avoid installing a > > migration entry if the swap entry is device-private. I don't have an > > exact fix yet due to my limited experience with core MM. The test case > > that triggers this is fairly simple: fault in a 2MB device page on the > > GPU, then fork a process that reads the page — the kernel crashes in > > this scenario. > > > > I'd be happy to look at any traces you have or post any fixes you have > > Thanks for the feedback > Balbir Singh >