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[85.23.51.1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-477bf1df392sm1633645e9.1.2025.11.20.09.43.42 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 20 Nov 2025 09:43:44 -0800 (PST) Message-ID: Date: Thu, 20 Nov 2025 19:43:42 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] fixup: mm/migrate_device: handle partially mapped folios during To: Matthew Brost , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-mm@kvack.org Cc: Andrew Morton , David Hildenbrand , Zi Yan , Joshua Hahn , Rakie Kim , Byungchul Park , Gregory Price , Ying Huang , Alistair Popple , Oscar Salvador , Lorenzo Stoakes , Baolin Wang , "Liam R . Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , Ralph Campbell , Francois Dugast , Balbir Singh References: <20251120170515.46504-1-matthew.brost@intel.com> Content-Language: en-US From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <20251120170515.46504-1-matthew.brost@intel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi, On 11/20/25 19:05, Matthew Brost wrote: > Splitting a partially mapped folio caused a regression in the Intel Xe > SVM test suite in the mremap section, resulting in the following stack > trace: > > NFO: task kworker/u65:2:1642 blocked for more than 30 seconds. > [ 212.624286] Tainted: G S W 6.18.0-rc6-xe+ #1719 > [ 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] > > The issue appears to be that migration PTEs are not properly removed > after a split. > > This change refactors the code to perform the split in a slightly > different manner while retaining the original patch’s intent. With this > update, the Intel Xe SVM test suite fully passes. > > Cc: Andrew Morton > Cc: David Hildenbrand > Cc: Zi Yan > Cc: Joshua Hahn > Cc: Rakie Kim > Cc: Byungchul Park > Cc: Gregory Price > Cc: Ying Huang > Cc: Alistair Popple > Cc: Oscar Salvador > Cc: Lorenzo Stoakes > Cc: Baolin Wang > Cc: Liam R. Howlett > Cc: Nico Pache > Cc: Ryan Roberts > Cc: Dev Jain > Cc: Barry Song > Cc: Lyude Paul > Cc: Danilo Krummrich > Cc: David Airlie > Cc: Simona Vetter > Cc: Ralph Campbell > Cc: Mika Penttilä > Cc: Francois Dugast > Cc: Balbir Singh > Signed-off-by: Matthew Brost > > --- > This fixup should be squashed into the patch "mm/migrate_device: handle > partially mapped folios during" in mm/mm-unstable > > I replaced the original patch with a local patch I authored a while back > that solves the same problem but uses a different code structure. The > failing test case—only available on an Xe driver—passes with this patch. > I can attempt to fix up the original patch within its structure if > that’s preferred. > --- > mm/migrate_device.c | 42 ++++++++++++++++++++++++------------------ > 1 file changed, 24 insertions(+), 18 deletions(-) > > diff --git a/mm/migrate_device.c b/mm/migrate_device.c > index fa42d2ebd024..69e88f4a2563 100644 > --- a/mm/migrate_device.c > +++ b/mm/migrate_device.c > @@ -254,6 +254,7 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > spinlock_t *ptl; > struct folio *fault_folio = migrate->fault_page ? > page_folio(migrate->fault_page) : NULL; > + struct folio *split_folio = NULL; > pte_t *ptep; > > again: > @@ -266,10 +267,11 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > return 0; > } > > - ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); > + ptep = pte_offset_map_lock(mm, pmdp, start, &ptl); > if (!ptep) > goto again; > arch_enter_lazy_mmu_mode(); > + ptep += (addr - start) / PAGE_SIZE; > > for (; addr < end; addr += PAGE_SIZE, ptep++) { > struct dev_pagemap *pgmap; > @@ -347,22 +349,6 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > pgmap->owner != migrate->pgmap_owner) > goto next; > } > - folio = page ? page_folio(page) : NULL; > - if (folio && folio_test_large(folio)) { > - int ret; > - > - pte_unmap_unlock(ptep, ptl); > - ret = migrate_vma_split_folio(folio, > - migrate->fault_page); > - > - if (ret) { > - ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); > - goto next; > - } > - > - addr = start; > - goto again; > - } > mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; > mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0; > } > @@ -400,6 +386,11 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > bool anon_exclusive; > pte_t swp_pte; > > + if (folio_order(folio)) { > + split_folio = folio; > + goto split; > + } > + > flush_cache_page(vma, addr, pte_pfn(pte)); > anon_exclusive = folio_test_anon(folio) && > PageAnonExclusive(page); > @@ -478,8 +469,23 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, > if (unmapped) > flush_tlb_range(walk->vma, start, end); > > +split: > arch_leave_lazy_mmu_mode(); > - pte_unmap_unlock(ptep - 1, ptl); > + pte_unmap_unlock(ptep - 1 + !!split_folio, ptl); > + > + if (split_folio) { > + int ret; > + > + ret = split_folio(split_folio); > + if (fault_folio != split_folio) > + folio_unlock(split_folio); I think wrong folio is left locked in case of fault_folio != NULL. Look how migrate_vma_split_folio() handles it. > + folio_put(split_folio); > + if (ret) > + return migrate_vma_collect_skip(addr, end, walk); > + > + split_folio = NULL; > + goto again; > + } > > return 0; > } How is this making a difference, I suppose it's only the migrate_vma_collect_skip() after failed split? Why are you just removing the other migrate_vma_split_folio() call? --Mika