When a CPU faults on a device private PMD and the device driver can only allocate order-0 destination folios, __migrate_device_pages() has to split the source THP via migrate_vma_split_unmapped_folio(). That path is broken in two independent ways when the fault is what triggered the migration. First, the split never succeeds. At the point folio_split_unmapped() is called the folio carries two references beyond the ones it is entitled to: 1 - taken by do_huge_pmd_device_private() for the duration of the ->migrate_to_ram() callback 2 - taken by migrate_vma_collect_huge_pmd() when the folio was collected (the mapping reference having been dropped by set_pmd_migration_entry()). folio_split_unmapped() requires folio_expected_ref_count(folio) == folio_ref_count(folio) - 1, i.e. it tolerates exactly one caller reference. With both of the above held the check sees 2 against an expected 0 and returns -EAGAIN, so the migration is abandoned and the CPU fault makes no progress. The PTE-based split path does not have this problem: migrate_vma_split_folio() is called before any collect reference is taken and explicitly skips folio_get() for the fault folio, so the fault reference is the single caller reference the split expects. Fix it by dropping the fault reference across the split and re-taking it afterwards. do_huge_pmd_device_private() derives the fault page from the PMD entry, so it is always the head page of the folio and always ends up in the head folio of an uniform split to order 0; re-taking the reference on the folio therefore puts it back exactly where do_huge_pmd_device_private() will release it. The folio cannot be freed while the reference is dropped because the collect reference is still held. Second, the folio is split globally but the page tables were demoted only locally: split_huge_pmd_address(migrate->vma, addr, true); ret = folio_split_unmapped(folio, 0); migrate_device_unmap() unmaps via try_to_migrate(folio, 0), deliberately without TTU_SPLIT_HUGE_PMD, so every VMA that PMD maps the folio is left holding a PMD sized migration entry. A folio that was PMD mapped in more than one VMA -- after fork(), for example -- therefore keeps huge migration entries in all the other VMAs while only migrate->vma is demoted. folio_split_unmapped() does not notice: the folio is fully unmapped, so it only looks at the refcount and happily splits to order 0. The other VMAs are then left pointing a huge PMD at an order-0 folio, and migrate_vma_finalize() -> remove_migration_ptes() walks into it: page dumped because: VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) || !folio_test_pmd_mappable(folio)) kernel BUG at mm/migrate.c:368! RIP: 0010:remove_migration_pte+0x56a/0x9b0 Call Trace: rmap_walk_anon+0xfc/0x260 remove_migration_ptes+0x79/0xb0 __migrate_device_finalize+0x113/0x290 __drm_pagemap_migrate_to_ram+0x278/0x360 [drm_gpusvm_helper] drm_pagemap_migrate_to_ram+0x5c/0x80 [drm_gpusvm_helper] do_huge_pmd_device_private+0x160/0x280 Without CONFIG_DEBUG_VM the VM_BUG_ON_FOLIO() is compiled out and remove_migration_pmd() installs a huge PMD pointing at an order-0 page instead, along with add_mm_counter(mm, MM_ANONPAGES, HPAGE_PMD_NR). The victim mm then maps 2MB of address space onto a single 4K page, which shows up later as bad rss-counter state, leaked page tables and page allocator freelist corruption in unrelated processes. Note this second problem was latent before the refcount fix above: the split always failed, and the failed attempt left migrate->vma demoted, so the retried fault took the PTE path, where __folio_split() unmaps with TTU_SPLIT_HUGE_PMD and demotes every VMA. Fix it by walking the rmap and demoting every PMD sized migration entry mapping the folio before splitting it. Demote with freeze = false: entry creation in __split_huge_pmd_locked() is dispatched on pmd_is_migration_entry(), not on freeze, so a migration PMD becomes PTE sized migration entries either way, and freeze only controls a trailing put_page(). With freeze = false there is no refcount change at all, which makes the demotion idempotent across N VMAs. rmap_walk_control.anon_lock is deliberately left unset: folio_lock_anon_vma_read() depends on folio_mapped(), and the folio is already fully unmapped here. This mirrors remove_migration_ptes(). Finally, refuse the split for a folio that is not anonymous. The rmap walk would otherwise reach a file backed VMA, where split_huge_pmd_address() zaps the PMD instead of demoting it. Fixes: 4265d67e405a ("mm/migrate_device: add THP splitting during migration") Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Balbir Singh Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: Thomas Hellström Cc: Francois Dugast Cc: dri-devel@lists.freedesktop.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Assisted-by: GitHub Copilot:claude-opus-5 Signed-off-by: Matthew Brost --- mm/migrate_device.c | 98 ++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 89 insertions(+), 9 deletions(-) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index 908d2d4ec43a..d1d81bbbf795 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -899,22 +899,104 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate, return 0; } +static bool migrate_vma_split_pmd_one(struct folio *folio, + struct vm_area_struct *vma, + unsigned long addr, void *arg) +{ + DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, addr, PVMW_SYNC | PVMW_MIGRATION); + + while (page_vma_mapped_walk(&pvmw)) { + if (pvmw.pte) + continue; + + addr = pvmw.address; + page_vma_mapped_walk_done(&pvmw); + + /* + * Demote with freeze = false: the PMD already holds a + * migration entry, so __split_huge_pmd_locked() creates PTE + * sized migration entries from it and leaves the refcount + * alone. There is at most one PMD mapping @folio per VMA, so + * stop the walk here. + */ + split_huge_pmd_address(vma, addr, false); + break; + } + + return true; +} + +/* + * Demote every PMD sized migration entry that maps @folio to PTE sized ones. + * + * migrate_device_unmap() unmaps with try_to_migrate(folio, 0), i.e. without + * TTU_SPLIT_HUGE_PMD, so a folio that was PMD mapped in several VMAs -- after + * fork(), for instance -- ends up with a PMD sized migration entry in every one + * of them. folio_split_unmapped() below does not care, it only looks at the + * refcount, so splitting the folio without demoting all of those first would + * leave the other VMAs pointing a huge PMD at what is now an order-0 folio. + * remove_migration_ptes() trips over that in migrate_vma_finalize(). + */ +static void migrate_vma_split_pmd_mappings(struct folio *folio) +{ + struct rmap_walk_control rwc = { + .rmap_one = migrate_vma_split_pmd_one, + }; + + /* + * Do not pass .anon_lock: folio_lock_anon_vma_read() requires + * folio_mapped(), and @folio is already fully unmapped here. + */ + rmap_walk(folio, &rwc); +} + static int migrate_vma_split_unmapped_folio(struct migrate_vma *migrate, - unsigned long idx, unsigned long addr, + unsigned long idx, struct folio *folio) { unsigned long i; unsigned long pfn; unsigned long flags; + bool fault_folio; int ret = 0; /* - * take a reference, since split_huge_pmd_address() with freeze = true - * drops a reference at the end. + * migrate_vma_split_pmd_mappings() walks the rmap, and + * split_huge_pmd_address() zaps rather than demotes a PMD in a VMA that + * is not anonymous. migrate_vma_collect_huge_pmd() does not check the + * VMA type, so a file THP can reach here; the rest of the migrate_vma() + * machinery only supports anonymous memory anyway. */ - folio_get(folio); - split_huge_pmd_address(migrate->vma, addr, true); + if (!folio_test_anon(folio)) + return -EINVAL; + + /* + * A CPU fault on a device private PMD holds an extra reference on the + * folio, taken by do_huge_pmd_device_private(). folio_split_unmapped() + * only tolerates a single caller reference, so the split would always + * fail with -EAGAIN while this fault reference is held. + * + * do_huge_pmd_device_private() derives the fault page from the PMD + * entry, so it is always the head page of @folio, and therefore always + * ends up in the head folio after an uniform split to order 0. Drop + * the reference across the split and re-take it on the head folio + * afterwards, leaving the reference exactly where it is expected to be + * released. + * + * The folio cannot go away while the reference is dropped: the + * reference taken by migrate_vma_collect_huge_pmd() is still held. + */ + fault_folio = migrate->fault_page && + page_folio(migrate->fault_page) == folio; + + migrate_vma_split_pmd_mappings(folio); + + if (fault_folio) + folio_put(folio); ret = folio_split_unmapped(folio, 0); + if (fault_folio) + folio_get(folio); + if (ret) return ret; migrate->src[idx] &= ~MIGRATE_PFN_COMPOUND; @@ -935,7 +1017,7 @@ static int migrate_vma_insert_huge_pmd_page(struct migrate_vma *migrate, } static int migrate_vma_split_unmapped_folio(struct migrate_vma *migrate, - unsigned long idx, unsigned long addr, + unsigned long idx, struct folio *folio) { return 0; @@ -1103,7 +1185,6 @@ static void __migrate_device_pages(unsigned long *src_pfns, struct mmu_notifier_range range; unsigned long i, j; bool notified = false; - unsigned long addr; for (i = 0; i < npages; ) { struct page *newpage = migrate_pfn_to_page(dst_pfns[i]); @@ -1177,8 +1258,7 @@ static void __migrate_device_pages(unsigned long *src_pfns, goto next; } nr = 1 << folio_order(folio); - addr = migrate->start + i * PAGE_SIZE; - if (migrate_vma_split_unmapped_folio(migrate, i, addr, folio)) { + if (migrate_vma_split_unmapped_folio(migrate, i, folio)) { src_pfns[i] &= ~(MIGRATE_PFN_MIGRATE | MIGRATE_PFN_COMPOUND); goto next; -- 2.34.1 __migrate_device_pages() computed extra_cnt once, from the head page of the source folio, and then passed the same value to folio_migrate_mapping() for every one of the @nr sub-folios produced by migrate_vma_split_unmapped_folio(). The extra reference the CPU fault holds only exists on the single folio that ends up containing the fault page. Claiming it for all of them makes folio_migrate_mapping() expect one reference too many on every other sub-folio, so it returns -EAGAIN and MIGRATE_PFN_MIGRATE is cleared for them. Only the fault page would migrate; the remaining HPAGE_PMD_NR - 1 pages would be restored to device memory, and the faulting access would immediately fault again. Compute extra_cnt per sub-folio instead, comparing against the source page for that entry. While at it, use the sub-folio's own mapping rather than the mapping that was read from the pre-split folio. This has been latent so far because the split it depends on could never succeed while the fault reference was held. Fixes: 4265d67e405a ("mm/migrate_device: add THP splitting during migration") Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Balbir Singh Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: Thomas Hellström Cc: Francois Dugast Cc: dri-devel@lists.freedesktop.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Assisted-by: GitHub Copilot:claude-opus-5 Signed-off-by: Matthew Brost --- mm/migrate_device.c | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/mm/migrate_device.c b/mm/migrate_device.c index d1d81bbbf795..65a6a15dba4d 100644 --- a/mm/migrate_device.c +++ b/mm/migrate_device.c @@ -1191,7 +1191,7 @@ static void __migrate_device_pages(unsigned long *src_pfns, struct page *page = migrate_pfn_to_page(src_pfns[i]); struct address_space *mapping; struct folio *newfolio, *folio; - int r, extra_cnt = 0; + int r; unsigned long nr = 1; if (!newpage) { @@ -1296,13 +1296,25 @@ static void __migrate_device_pages(unsigned long *src_pfns, BUG_ON(folio_test_writeback(folio)); - if (migrate && migrate->fault_page == page) - extra_cnt = 1; for (j = 0; j < nr && i + j < npages; j++) { - folio = page_folio(migrate_pfn_to_page(src_pfns[i+j])); + struct page *src_page = migrate_pfn_to_page(src_pfns[i+j]); + int extra_cnt = 0; + + folio = page_folio(src_page); newfolio = page_folio(migrate_pfn_to_page(dst_pfns[i+j])); - r = folio_migrate_mapping(mapping, newfolio, folio, extra_cnt); + /* + * The CPU fault holds an extra reference on the folio + * containing the fault page. @folio may have been + * split above, so the fault page only accounts for an + * extra reference on the folio it actually ended up + * in, not on every folio of the original THP. + */ + if (migrate && migrate->fault_page == src_page) + extra_cnt = 1; + + r = folio_migrate_mapping(folio_mapping(folio), newfolio, + folio, extra_cnt); if (r) src_pfns[i+j] &= ~MIGRATE_PFN_MIGRATE; else -- 2.34.1 drm_pagemap_migrate_populate_ram_pfn() had two issues when populating RAM PFNs with higher-order folios: 1. The higher-order vma_alloc_folio()/folio_alloc() calls did not pass __GFP_NOWARN, so a THP allocation failure under memory pressure would spam the kernel log, and there was no fallback path despite a TODO comment stating one was needed. Add __GFP_NOWARN to the higher-order allocation and, on failure, fall back to order-0 allocations for the entire range originally covered by the failed higher-order allocation, leaving MIGRATE_PFN_COMPOUND unset for those PFNs. 2. In the free_pages error path, order was computed via folio_order(page_folio(page)) *after* put_page(page) had already dropped the reference, resulting in a use-after-free/put when that was the last reference on the page. Compute order before releasing the page. Introducing the fallback in 1. also requires the source page array handed to ->copy_to_ram() to be built differently. Both callers only populated the entry at the head of each source folio, relying on the copy callback to derive the rest of the folio from the order recorded in the matching drm_pagemap_addr. Once the destination has been demoted to order-0 folios the drm_pagemap_addr entries are per-page, so a source page is needed for every one of them; leaving them NULL makes the copy callback stop after the first page and the remainder of the range is never copied. The source folio is only split later, by migrate_vma_pages() / migrate_device_pages(), so its order cannot be used to detect the demotion - test the destination for MIGRATE_PFN_COMPOUND instead. Factor the array population out into drm_pagemap_migrate_populate_src_pages() and use it from both drm_pagemap_evict_to_ram() and __drm_pagemap_migrate_to_ram(). Fixes: ddeda6136038 ("drm/pagemap: Allocate folios when possible") Cc: stable@vger.kernel.org Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Balbir Singh Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: Thomas Hellström Cc: Francois Dugast Cc: dri-devel@lists.freedesktop.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Assisted-by: GitHub Copilot:claude-opus-5 Signed-off-by: Matthew Brost --- drivers/gpu/drm/drm_pagemap.c | 114 ++++++++++++++++++++++++++-------- 1 file changed, 89 insertions(+), 25 deletions(-) diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c index 892b325fa99b..7610e233d238 100644 --- a/drivers/gpu/drm/drm_pagemap.c +++ b/drivers/gpu/drm/drm_pagemap.c @@ -383,6 +383,58 @@ drm_pagemap_migrate_map_system_pages(struct device *dev, return 0; } +/** + * drm_pagemap_migrate_populate_src_pages() - Populate the source page array + * @pages: Array of source pages to populate + * @src_mpfn: Source array of migrate PFNs + * @dst_mpfn: Destination array of migrate PFNs + * @npages: Number of pages in the arrays + * + * Populate @pages with the device pages the copy callback is to read from. + * + * Entries are normally only populated at the head of each source folio, with + * the copy callback deriving the rest of the folio from the order recorded in + * the corresponding drm_pagemap_addr. That does not work where + * drm_pagemap_migrate_populate_ram_pfn() had to demote a higher-order source + * folio to order-0 destination folios: the drm_pagemap_addr entries are then + * per-page, and the copy callback needs a source page for each of them. + * Populate every entry for those ranges. + * + * Note that the source folio itself is only split later, by + * migrate_vma_pages() / migrate_device_pages(), so its order cannot be used to + * detect the demotion - the destination has to be inspected instead. + */ +static void drm_pagemap_migrate_populate_src_pages(struct page **pages, + unsigned long *src_mpfn, + unsigned long *dst_mpfn, + unsigned long npages) +{ + unsigned long i; + + for (i = 0; i < npages;) { + struct page *page = migrate_pfn_to_page(src_mpfn[i]); + unsigned int order = 0; + unsigned long j, nr; + + if (!page) { + i++; + continue; + } + + order = folio_order(page_folio(page)); + nr = NR_PAGES(order); + + if (order && !(dst_mpfn[i] & MIGRATE_PFN_COMPOUND)) { + for (j = 0; j < nr && i + j < npages; j++) + pages[i + j] = folio_page(page_folio(page), j); + } else { + pages[i] = page; + } + + i += nr; + } +} + /** * drm_pagemap_migrate_unmap_pages() - Unmap pages previously mapped for GPU SVM migration * @dev: The device for which the pages were mapped @@ -875,6 +927,7 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas, struct page *page = NULL, *src_page; struct folio *folio; unsigned int order = 0; + gfp_t gfp = GFP_HIGHUSER; if (!(src_mpfn[i] & MIGRATE_PFN_MIGRATE)) goto next; @@ -890,12 +943,38 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas, } order = folio_order(page_folio(src_page)); + if (order) + gfp |= __GFP_NOWARN; - /* TODO: Support fallback to single pages if THP allocation fails */ if (vas) - folio = vma_alloc_folio(GFP_HIGHUSER, order, vas, addr); + folio = vma_alloc_folio(gfp, order, vas, addr); else - folio = folio_alloc(GFP_HIGHUSER, order); + folio = folio_alloc(gfp, order); + + if (!folio && order) { + /* + * Higher-order allocation failed, fall back to + * order-0 allocations for the entire range covered + * by the original higher-order allocation, without + * setting MIGRATE_PFN_COMPOUND, until we move past + * that range. + */ + unsigned long nr = NR_PAGES(order); + unsigned long j; + + gfp &= ~__GFP_NOWARN; + for (j = 0; j < nr && i < npages; j++, i++, addr += PAGE_SIZE) { + folio = vas ? + vma_alloc_folio(gfp, 0, vas, addr) : + folio_alloc(gfp, 0); + if (!folio) + goto free_pages; + + page = folio_page(folio, 0); + mpfn[i] = migrate_pfn(page_to_pfn(page)); + } + continue; + } if (!folio) goto free_pages; @@ -940,11 +1019,11 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas, if (!page) goto next_put; + order = folio_order(page_folio(page)); + put_page(page); mpfn[i] = 0; - order = folio_order(page_folio(page)); - next_put: i += NR_PAGES(order); } @@ -1120,7 +1199,7 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem *devmem_allocation) unsigned long *src, *dst; struct drm_pagemap_addr *pagemap_addr; void *buf; - int i, err = 0; + int err = 0; unsigned int retry_count = 2; npages = devmem_allocation->size >> PAGE_SHIFT; @@ -1160,15 +1239,7 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem *devmem_allocation) if (err) goto err_finalize; - for (i = 0; i < npages;) { - unsigned int order = 0; - - pages[i] = migrate_pfn_to_page(src[i]); - if (pages[i]) - order = folio_order(page_folio(pages[i])); - - i += NR_PAGES(order); - } + drm_pagemap_migrate_populate_src_pages(pages, src, dst, npages); err = ops->copy_to_ram(pages, pagemap_addr, npages, NULL); if (err) @@ -1235,7 +1306,7 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas, struct drm_pagemap_addr *pagemap_addr; unsigned long start, end; void *buf; - int i, err = 0; + int err = 0; zdd = drm_pagemap_page_zone_device_data(page); if (time_before64(get_jiffies_64(), zdd->devmem_allocation->timeslice_expiration)) @@ -1290,15 +1361,8 @@ static int __drm_pagemap_migrate_to_ram(struct vm_area_struct *vas, if (err) goto err_finalize; - for (i = 0; i < npages;) { - unsigned int order = 0; - - pages[i] = migrate_pfn_to_page(migrate.src[i]); - if (pages[i]) - order = folio_order(page_folio(pages[i])); - - i += NR_PAGES(order); - } + drm_pagemap_migrate_populate_src_pages(pages, migrate.src, migrate.dst, + npages); err = ops->copy_to_ram(pages, pagemap_addr, npages, NULL); if (err) -- 2.34.1 Migrating a device-private THP back to system memory has two distinct paths in __migrate_device_pages(): the fast path where both source and destination carry MIGRATE_PFN_COMPOUND, and the fallback path where the destination could only be satisfied with order-0 folios and the source THP therefore has to be split via migrate_vma_split_unmapped_folio(). The fallback path only triggers under genuine memory pressure, which makes it both rare and awkward to reproduce, yet it is the path where the interesting refcounting happens (the CPU fault holds an extra reference on the device folio taken by do_huge_pmd_device_private()). Add a fault_attr, modelled on backup_fault_inject in ttm_pool.c, that forces the higher-order allocation in drm_pagemap_migrate_populate_ram_pfn() to fail so the existing order-0 fallback is taken deterministically. The attribute is exposed at /sys/kernel/debug/drm_pagemap_fault_inject and requires CONFIG_FAULT_INJECTION_DEBUG_FS. With CONFIG_FAULT_INJECTION disabled the helper compiles out to a constant false and the injection has no cost. Cc: Andrew Morton Cc: David Hildenbrand Cc: Lorenzo Stoakes Cc: Zi Yan Cc: Baolin Wang Cc: Liam R. Howlett Cc: Nico Pache Cc: Ryan Roberts Cc: Dev Jain Cc: Barry Song Cc: Lance Yang Cc: Usama Arif Cc: Joshua Hahn Cc: Rakie Kim Cc: Byungchul Park Cc: Gregory Price Cc: Ying Huang Cc: Alistair Popple Cc: Balbir Singh Cc: Maarten Lankhorst Cc: Maxime Ripard Cc: Thomas Zimmermann Cc: David Airlie Cc: Simona Vetter Cc: Thomas Hellström Cc: Francois Dugast Cc: dri-devel@lists.freedesktop.org Cc: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org Assisted-by: GitHub Copilot:claude-opus-5 Signed-off-by: Matthew Brost --- drivers/gpu/drm/drm_pagemap.c | 36 ++++++++++++++++++++++++++++++++++- 1 file changed, 35 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_pagemap.c b/drivers/gpu/drm/drm_pagemap.c index 7610e233d238..01eb29ef023c 100644 --- a/drivers/gpu/drm/drm_pagemap.c +++ b/drivers/gpu/drm/drm_pagemap.c @@ -3,6 +3,7 @@ * Copyright © 2024-2025 Intel Corporation */ +#include #include #include #include @@ -12,6 +13,27 @@ #include #include +#ifdef CONFIG_FAULT_INJECTION +#include +static DECLARE_FAULT_ATTR(migrate_to_ram_fault_inject); + +/* + * Force a higher-order destination folio allocation to fail in + * drm_pagemap_migrate_populate_ram_pfn(), exercising the order-0 fallback + * (and, in turn, the THP split path in __migrate_device_pages()) without + * having to drive the system into actual memory pressure. + */ +static bool drm_pagemap_fault_inject_folio(void) +{ + return should_fail(&migrate_to_ram_fault_inject, 1); +} +#else +static bool drm_pagemap_fault_inject_folio(void) +{ + return false; +} +#endif + /** * DOC: Overview * @@ -946,7 +968,9 @@ static int drm_pagemap_migrate_populate_ram_pfn(struct vm_area_struct *vas, if (order) gfp |= __GFP_NOWARN; - if (vas) + if (order && drm_pagemap_fault_inject_folio()) + folio = NULL; + else if (vas) folio = vma_alloc_folio(gfp, order, vas, addr); else folio = folio_alloc(gfp, order); @@ -1540,6 +1564,16 @@ void drm_pagemap_destroy(struct drm_pagemap *dpagemap, bool is_atomic_or_reclaim kfree(dpagemap); } +static int __init drm_pagemap_module_init(void) +{ +#if defined(CONFIG_DEBUG_FS) && defined(CONFIG_FAULT_INJECTION) + fault_create_debugfs_attr("drm_pagemap_fault_inject", NULL, + &migrate_to_ram_fault_inject); +#endif + return 0; +} +module_init(drm_pagemap_module_init); + static void drm_pagemap_exit(void) { flush_work(&drm_pagemap_work); -- 2.34.1