Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
Pre-existing issues: - [High] Double migration of device pages due to missing flag in peer-to-peer migration. - [High] DMA mappings are leaked on the error path because the destination PFN array is zeroed out before unmapping. - [High] Use-after-free of folio metadata in the error path of `drm_pagemap_migrate_populate_ram_pfn`. -- --- Patch [1]: [PATCH v4] drm/pagemap: Prevent double migration of device pages --- commit ddf1406cd4fcd17693eecb3abf05b87068425942 Author: Arvind Yadav <[email protected]> Subject: drm/pagemap: Prevent double migration of device pages This patch addresses a double migration bug involving device-private folios. It flags successfully migrated device folios using a low bit in their zone_device_data before migration finalization, ensuring that raw-PFN eviction paths skip them. > --- a/drivers/gpu/drm/drm_pagemap.c > +++ b/drivers/gpu/drm/drm_pagemap.c [ ... ] > @@ -1143,6 +1250,8 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem > *devmem_allocation) > if (err) > goto err_free; > > + drm_pagemap_skip_retired_pages(src, npages); > + > err = drm_pagemap_migrate_populate_ram_pfn(NULL, NULL, npages, &mpages, > src, dst, 0); [Severity: High] This is a pre-existing issue, but does this call to drm_pagemap_migrate_populate_ram_pfn() trigger a use-after-free on its error path? If page allocation fails inside drm_pagemap_migrate_populate_ram_pfn(), the cleanup path jumps to the free_pages label: free_pages: for (i = 0; i < npages;) { struct page *page = migrate_pfn_to_page(mpfn[i]); unsigned int order = 0; if (!page) goto next_put; put_page(page); mpfn[i] = 0; order = folio_order(page_folio(page)); Is it safe to read the folio_order metadata after put_page() has dropped the reference and potentially freed the page? It looks like this could result in garbage order values, leading to incorrect loop increments and missed cleanups. > if (err || !mpages) > goto err_finalize; [ ... ] > @@ -1173,6 +1282,7 @@ int drm_pagemap_evict_to_ram(struct drm_pagemap_devmem > *devmem_allocation) > if (err) > drm_pagemap_migration_unlock_put_pages(npages, dst); > migrate_device_pages(src, dst, npages); > + drm_pagemap_retire_migrated_pages(src, npages); > migrate_device_finalize(src, dst, npages); > drm_pagemap_migrate_unmap_pages(devmem_allocation->dev, pagemap_addr, > dst, npages, > DMA_FROM_DEVICE, &state); [Severity: High] This is a pre-existing issue, but I am wondering if the peer-to-peer migration path is also vulnerable to this same double-migration bug? Looking at drm_pagemap_migrate_to_devmem(), it finalizes the migration without calling drm_pagemap_retire_migrated_pages() to set the flag on the source folio: err_aborted_migration: migrate_vma_pages(&migrate); for (i = 0; !err && i < npages;) { ... migrate_vma_finalize(&migrate); Could a concurrent eviction select the same device folio, fail to skip it since the migrated flag is missing, and attempt to migrate it again? [ ... ] > @@ -1303,6 +1413,7 @@ static int __drm_pagemap_migrate_to_ram(struct > vm_area_struct *vas, > if (err) > drm_pagemap_migration_unlock_put_pages(npages, migrate.dst); > migrate_vma_pages(&migrate); > + drm_pagemap_retire_migrated_pages(migrate.src, npages); > migrate_vma_finalize(&migrate); > if (dev) > drm_pagemap_migrate_unmap_pages(dev, pagemap_addr, migrate.dst, [Severity: High] This is a pre-existing issue, but does this error path permanently leak DMA mappings? If an error occurs, drm_pagemap_migration_unlock_put_pages() is called, which zeroes out the migrate.dst array internally: static void drm_pagemap_migration_unlock_put_pages(...) { ... drm_pagemap_migration_unlock_put_folio(folio); migrate_pfn[i] = 0; ... } Then shortly after, we pass that same zeroed array to drm_pagemap_migrate_unmap_pages(). Inside drm_pagemap_migrate_unmap_pages(), it retrieves the page: struct page *page = migrate_pfn_to_page(migrate_pfn[i]); if (!page || !pagemap_addr[i].addr || dma_mapping_error(...)) goto next; Since the array entries were zeroed, migrate_pfn_to_page(0) returns NULL, causing the loop to bypass dma_unmap_page() entirely. > npages, DMA_FROM_DEVICE, > &state); > err_free: [ ... ] -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
