On Thu, 2026-07-02 at 14:48 -0700, Matthew Brost wrote: > Pages in ttm_pool_backup can be NULL or backup handles > (ttm_backup_page_ptr_is_handle()), neither of which can be passed to > set_pages_array_wb() or freed. Add a dedicated WB pass before the > dma/purge loop that walks allocations using the same i += num_pages > stride, skipping NULL and handle entries, and calls > set_pages_array_wb() > once per contiguous run of real pages. Apply the same NULL/handle > guard > to the dma/purge loop. > > Fixes the following oops: > > Oops: general protection fault, kernel NULL pointer dereference 0x0: > 0000 [#1] SMP NOPTI > RIP: 0010:__cpa_process_fault+0xf8/0x770 > RSP: 0018:ffffc90000a87718 EFLAGS: 00010287 > RAX: 0000000000000000 RBX: ffffc90000a87868 RCX: 0000000000000000 > RDX: 0000000000001000 RSI: 0005088000000000 RDI: ffffffff827c5f34 > RBP: 0005088000000000 R08: ffffc90000a877cb R09: ffffc90000a877d0 > R10: 0000000000000000 R11: 000000000000001b R12: 000ffffffffff000 > R13: ffffc90000a87868 R14: ffffc90000a87868 R15: ffff88815b882ae0 > FS: 0000000000000000(0000) GS:ffff8884ec840000(0000) > knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007f930b844000 CR3: 000000000262e003 CR4: 0000000008f70ef0 > PKRU: 55555554 > Call Trace: > <TASK> > __change_page_attr_set_clr+0x989/0xe90 > ? __purge_vmap_area_lazy+0x6c/0x3a0 > ? _vm_unmap_aliases+0x250/0x2a0 > set_pages_array_wb+0x7f/0x120 > ttm_pool_backup+0x4c9/0x5b0 [ttm] > ? dma_resv_wait_timeout+0x3b/0xf0 > ttm_tt_backup+0x32/0x60 [ttm] > ttm_bo_shrink+0x66/0x110 [ttm] > xe_bo_shrink_purge+0x12b/0x1b0 [xe] > xe_bo_shrink+0xbb/0x270 [xe] > __xe_shrinker_walk+0xf7/0x160 [xe] > xe_shrinker_walk+0x9d/0xc0 [xe] > xe_shrinker_scan+0x11f/0x210 [xe] > do_shrink_slab+0x13b/0x270 > shrink_slab+0xf1/0x400 > shrink_node+0x352/0x8a0 > balance_pgdat+0x32c/0x700 > kswapd+0x205/0x2f0 > ? __pfx_autoremove_wake_function+0x10/0x10 > ? __pfx_kswapd+0x10/0x10 > kthread+0xd1/0x110 > ? __pfx_kthread+0x10/0x10 > ret_from_fork+0x1b1/0x200 > ? __pfx_kthread+0x10/0x10 > ret_from_fork_asm+0x1a/0x30 > </TASK> > > Cc: Christian Koenig <[email protected]> > Cc: Huang Rui <[email protected]> > Cc: Matthew Auld <[email protected]> > Cc: Matthew Brost <[email protected]> > Cc: Maarten Lankhorst <[email protected]> > Cc: Maxime Ripard <[email protected]> > Cc: Thomas Zimmermann <[email protected]> > Cc: David Airlie <[email protected]> > Cc: Simona Vetter <[email protected]> > Cc: Thomas Hellström <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Fixes: b63d715b8090 ("drm/ttm/pool, drm/ttm/tt: Provide a helper to > shrink pages") > Cc: [email protected] > Assisted-by: GitHub_Copilot:claude-opus-4.8 > Signed-off-by: Matthew Brost <[email protected]>
Reviewed-by: Thomas Hellström <[email protected]> > --- > drivers/gpu/drm/ttm/ttm_pool.c | 30 ++++++++++++++++++++++++++---- > 1 file changed, 26 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/ttm/ttm_pool.c > b/drivers/gpu/drm/ttm/ttm_pool.c > index 3d5f2ae0a456..ff043420d517 100644 > --- a/drivers/gpu/drm/ttm/ttm_pool.c > +++ b/drivers/gpu/drm/ttm/ttm_pool.c > @@ -1065,9 +1065,31 @@ long ttm_pool_backup(struct ttm_pool *pool, > struct ttm_tt *tt, > return -EBUSY; > > #ifdef CONFIG_X86 > - /* Anything returned to the system needs to be cached. */ > - if (tt->caching != ttm_cached) > - set_pages_array_wb(tt->pages, tt->num_pages); > + /* Anything returned to the system needs to be cached. Walk > allocations > + * skipping NULL pages and issue set_pages_array_wb() per > contiguous run. > + */ > + if (tt->caching != ttm_cached) { > + pgoff_t run_start = 0, run_count = 0; > + > + for (i = 0; i < tt->num_pages; i += num_pages) { > + page = tt->pages[i]; > + if (unlikely(!page || > ttm_backup_page_ptr_is_handle(page))) { > + if (run_count) { > + set_pages_array_wb(&tt- > >pages[run_start], > + > run_count); > + run_count = 0; > + } > + num_pages = 1; > + continue; > + } > + num_pages = 1UL << ttm_pool_page_order(pool, > page); > + if (!run_count) > + run_start = i; > + run_count += num_pages; > + } > + if (run_count) > + set_pages_array_wb(&tt->pages[run_start], > run_count); > + } > #endif > > if (tt->dma_address || flags->purge) { > @@ -1075,7 +1097,7 @@ long ttm_pool_backup(struct ttm_pool *pool, > struct ttm_tt *tt, > unsigned int order; > > page = tt->pages[i]; > - if (unlikely(!page)) { > + if (unlikely(!page || > ttm_backup_page_ptr_is_handle(page))) { > num_pages = 1; > continue; > }
