Re: [PATCH 5/5] drm/xe/vram: add early VRAM health check

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Sep 01, 2026 at 09:33:21AM +0100, Matthew Auld wrote:
> On 28/08/2026 17:37, Summers, Stuart wrote:
> > On Fri, 2026-08-28 at 16:14 +0100, Matthew Auld wrote:
> > > During early probe, use the last page as a canary for BAR sizing, CCS
> > > sizing, identity map setup etc. If something is wrong the last page
> > > is
> > > where we will likely find it. Hit it with everything we have. For now
> > 
> > Sorry coming in a little late here... but why only the last page and
> > not implementing a full per byte/bit memory test to trigger any
> > potential memory scanning on bit errors? Or is this not the intent
> > here?
> 
> Current scope was just to catch obvious sizing errors, which will likely
> show up in the last page (BAR, CCS, identity map). In particular this was
> meant as a regression test for the bug Linus hit, where we had incorrect
> VRAM/CCS sizing.
> 
> Also, this is hopefully non-destructive, since it gets triggered in CI on
> probe. Also means it needs to be fast. We could extend this in the future as
> needed.

+1 on the approach.

One nit with this patch: the commit message doesn't explain how the test
catches this bug, or even what the test is actually doing. I reverse
engineered the test and the code makes sense, but I'd suggest updating
the commit message to describe the test case and how it exercises the
bug.

Matt

> 
> > 
> > If this is a production scenario, the last page makes sense, but if
> > we're already wrapping this in a debug config...
> > 
> > Thanks,
> > Stuart
> > 
> > > this is gated behind a debug config option, so shouldn't trigger on
> > > production.
> > > 
> > > Main motivation is around CCS sizing where on some BMG cards the CCS
> > > offset is programmed misaligned, for whatever reason, and our
> > > handling
> > > of that was busted, as found by Linus, leading to some amount of CCS
> > > storage getting pulled into the allocator as normal VRAM.
> > > 
> > > Nothing in our CI farm has such a misaligned offset it would seem,
> > > however I did get this to pop on my b570, which does also have the
> > > misaligned CCS offset:
> > > 
> > >    Tile 0: Running VRAM memtest...
> > >    Tile 0: VRAM bounds overlap CCS region! VRAM sizing is incorrect.
> > > 
> > > With the fix from Linus, this goes away:
> > > 
> > >    Tile 0: Running VRAM memtest...
> > >    Tile 0: VRAM memtest completed.
> > > 
> > > Assisted-by: Gemini:gemini-3.1-pro-preview
> > > Signed-off-by: Matthew Auld <matthew.auld@intel.com>
> > > Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
> > > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > > Cc: Matthew Brost <matthew.brost@intel.com>
> > > Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > ---
> > >   drivers/gpu/drm/xe/xe_device.c     |   8 +
> > >   drivers/gpu/drm/xe/xe_migrate.c    |  64 ++++++++
> > >   drivers/gpu/drm/xe/xe_migrate.h    |   6 +
> > >   drivers/gpu/drm/xe/xe_tile_types.h |   4 +
> > >   drivers/gpu/drm/xe/xe_vram.c       | 241
> > > +++++++++++++++++++++++++++++
> > >   drivers/gpu/drm/xe/xe_vram.h       |  10 ++
> > >   6 files changed, 333 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/xe/xe_device.c
> > > b/drivers/gpu/drm/xe/xe_device.c
> > > index 82e0a555fa69..80008bf5776c 100644
> > > --- a/drivers/gpu/drm/xe/xe_device.c
> > > +++ b/drivers/gpu/drm/xe/xe_device.c
> > > @@ -1051,6 +1051,10 @@ int xe_device_probe(struct xe_device *xe)
> > >          if (err)
> > >                  return err;
> > > +       err = xe_vram_reserve_memtest_bo(xe);
> > > +       if (err)
> > > +               return err;
> > > +
> > >          for_each_tile(tile, xe, id) {
> > >                  err = xe_tile_init(tile);
> > >                  if (err)
> > > @@ -1067,6 +1071,10 @@ int xe_device_probe(struct xe_device *xe)
> > >                          return err;
> > >          }
> > > +       err = xe_vram_memtest(xe);
> > > +       if (err)
> > > +               return err;
> > > +
> > >          err = xe_pagefault_init(xe);
> > >          if (err)
> > >                  return err;
> > > diff --git a/drivers/gpu/drm/xe/xe_migrate.c
> > > b/drivers/gpu/drm/xe/xe_migrate.c
> > > index 0bf000d7c901..ff45c24d8889 100644
> > > --- a/drivers/gpu/drm/xe/xe_migrate.c
> > > +++ b/drivers/gpu/drm/xe/xe_migrate.c
> > > @@ -2650,3 +2650,67 @@ void xe_migrate_job_lock_assert(struct
> > > xe_exec_queue *q)
> > >   #if IS_ENABLED(CONFIG_DRM_XE_KUNIT_TEST)
> > >   #include "tests/xe_migrate.c"
> > >   #endif
> > > +
> > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_MEM)
> > > +int xe_migrate_debug_ccs_overlap(struct xe_migrate *m,
> > > +                                struct xe_bo *scratch_bo,
> > > +                                bool write_to_ccs)
> > > +{
> > > +       struct xe_device *xe = tile_to_xe(m->tile);
> > > +       struct xe_gt *gt = m->tile->primary_gt;
> > > +       struct dma_fence *fence;
> > > +       struct xe_bb *bb;
> > > +       struct xe_sched_job *job;
> > > +       u64 first_page_dpa, clear_L0_ofs, scratch_dpa,
> > > scratch_L0_ofs;
> > > +
> > > +       if (!xe_device_has_flat_ccs(xe))
> > > +               return -EINVAL;
> > > +
> > > +       first_page_dpa = xe_vram_region_dpa_base(m->tile->mem.vram);
> > > +       clear_L0_ofs = xe_migrate_vram_ofs(xe, first_page_dpa, true);
> > > +
> > > +       scratch_dpa = xe_bo_addr(scratch_bo, 0, XE_PAGE_SIZE);
> > > +       scratch_L0_ofs = xe_migrate_vram_ofs(xe, scratch_dpa, false);
> > > +
> > > +       bb = xe_bb_new(gt, EMIT_COPY_CCS_DW + 1, xe->info.has_usm);
> > > +       if (IS_ERR(bb)) {
> > > +               drm_warn(&xe->drm, "Failed to create bb for VRAM
> > > overlap check\n");
> > > +               return PTR_ERR(bb);
> > > +       }
> > > +
> > > +       /* 4MB payload = 8KB CCS metadata */
> > > +       if (write_to_ccs) {
> > > +               emit_copy_ccs(gt, bb, clear_L0_ofs, true,
> > > +                             scratch_L0_ofs, false, SZ_4M);
> > > +       } else {
> > > +               emit_copy_ccs(gt, bb, scratch_L0_ofs, false,
> > > +                             clear_L0_ofs, true, SZ_4M);
> > > +       }
> > > +
> > > +       bb->cs[bb->len++] = MI_BATCH_BUFFER_END;
> > > +
> > > +       job = xe_bb_create_migration_job(m->q, bb,
> > > +                                        xe_migrate_batch_base(m, xe-
> > > > info.has_usm),
> > > +                                        0);
> > > +       if (!IS_ERR(job)) {
> > > +               xe_sched_job_add_migrate_flush(job, MI_FLUSH_DW_CCS);
> > > +
> > > +               mutex_lock(&m->job_mutex);
> > > +               xe_sched_job_arm(job);
> > > +
> > > +               fence = dma_fence_get(&job->drm.s_fence->finished);
> > > +               xe_sched_job_push(job);
> > > +               mutex_unlock(&m->job_mutex);
> > > +
> > > +               dma_fence_wait(fence, false);
> > > +               dma_fence_put(fence);
> > > +       } else {
> > > +               drm_warn(&xe->drm, "Failed to create job for VRAM
> > > overlap check\n");
> > > +               xe_bb_free(bb, NULL);
> > > +               return PTR_ERR(job);
> > > +       }
> > > +
> > > +       xe_bb_free(bb, NULL);
> > > +       return 0;
> > > +}
> > > +#endif
> > > diff --git a/drivers/gpu/drm/xe/xe_migrate.h
> > > b/drivers/gpu/drm/xe/xe_migrate.h
> > > index c3a268b01768..a9acc62f78f0 100644
> > > --- a/drivers/gpu/drm/xe/xe_migrate.h
> > > +++ b/drivers/gpu/drm/xe/xe_migrate.h
> > > @@ -182,4 +182,10 @@ static inline void
> > > xe_migrate_job_lock_assert(struct xe_exec_queue *q)
> > >   void xe_migrate_job_lock(struct xe_migrate *m, struct xe_exec_queue
> > > *q);
> > >   void xe_migrate_job_unlock(struct xe_migrate *m, struct
> > > xe_exec_queue *q);
> > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_MEM)
> > > +int xe_migrate_debug_ccs_overlap(struct xe_migrate *m,
> > > +                                struct xe_bo *scratch_bo,
> > > +                                bool write_to_ccs);
> > > +#endif
> > > +
> > >   #endif
> > > diff --git a/drivers/gpu/drm/xe/xe_tile_types.h
> > > b/drivers/gpu/drm/xe/xe_tile_types.h
> > > index 0048100ccb72..e1368c04846a 100644
> > > --- a/drivers/gpu/drm/xe/xe_tile_types.h
> > > +++ b/drivers/gpu/drm/xe/xe_tile_types.h
> > > @@ -97,6 +97,10 @@ struct xe_tile {
> > >                   * Only main GT has page reclaim list allocations.
> > >                   */
> > >                  struct xe_sa_manager *reclaim_pool;
> > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_MEM)
> > > +               /** @mem.memtest_bo: VRAM overlap check BO */
> > > +               struct xe_bo *memtest_bo;
> > > +#endif
> > >          } mem;
> > >          /** @sriov: tile level virtualization data */
> > > diff --git a/drivers/gpu/drm/xe/xe_vram.c
> > > b/drivers/gpu/drm/xe/xe_vram.c
> > > index 0a2f1ab8416e..4a79580c5315 100644
> > > --- a/drivers/gpu/drm/xe/xe_vram.c
> > > +++ b/drivers/gpu/drm/xe/xe_vram.c
> > > @@ -17,8 +17,11 @@
> > >   #include "xe_device.h"
> > >   #include "xe_force_wake.h"
> > >   #include "xe_gt_mcr.h"
> > > +#include "xe_map.h"
> > > +#include "xe_migrate.h"
> > >   #include "xe_mmio.h"
> > >   #include "xe_sriov.h"
> > > +#include "xe_tile.h"
> > >   #include "xe_tile_sriov_vf.h"
> > >   #include "xe_ttm_vram_mgr.h"
> > >   #include "xe_vram.h"
> > > @@ -403,3 +406,241 @@ resource_size_t
> > > xe_vram_region_actual_physical_size(const struct xe_vram_region
> > >          return vram ? vram->actual_physical_size : 0;
> > >   }
> > >   EXPORT_SYMBOL_IF_KUNIT(xe_vram_region_actual_physical_size);
> > > +
> > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_MEM)
> > > +static void memtest_bo_cleanup(void *arg)
> > > +{
> > > +       struct xe_device *xe = arg;
> > > +
> > > +       xe_vram_free_memtest_bos(xe);
> > > +}
> > > +
> > > +int xe_vram_reserve_memtest_bo(struct xe_device *xe)
> > > +{
> > > +       struct xe_tile *tile;
> > > +       u8 id;
> > > +
> > > +       if (IS_SRIOV_VF(xe))
> > > +               return 0;
> > > +
> > > +       for_each_tile(tile, xe, id) {
> > > +               u64 vram_size;
> > > +
> > > +               if (!tile->mem.vram)
> > > +                       continue;
> > > +
> > > +               if (tile->mem.vram->io_size < tile->mem.vram-
> > > > usable_size) {
> > > +                       drm_info(&xe->drm,
> > > +                                "Tile %d: Small-BAR system detected,
> > > skipping VRAM memtest\n",
> > > +                                id);
> > > +                       continue;
> > > +               }
> > > +
> > > +               vram_size = tile->mem.vram->usable_size;
> > > +
> > > +               tile->mem.memtest_bo =
> > > xe_bo_create_pin_map_at_novm(xe, tile, SZ_64K,
> > > +
> > > vram_size - SZ_64K,
> > > +
> > > ttm_bo_type_kernel,
> > > +
> > > XE_BO_FLAG_VRAM_IF_DGFX(tile),
> > > +
> > > 0, false);
> > > +               if (IS_ERR(tile->mem.memtest_bo)) {
> > > +                       drm_warn(&xe->drm, "Tile %d: Failed to
> > > reserve memtest BO\n", id);
> > > +                       tile->mem.memtest_bo = NULL;
> > > +                       continue;
> > > +               }
> > > +
> > > +               drm_info(&xe->drm, "Tile %d: Reserved memtest BO at
> > > offset 0x%llx\n",
> > > +                        id, vram_size - SZ_64K);
> > > +       }
> > > +
> > > +       return devm_add_action_or_reset(xe->drm.dev,
> > > memtest_bo_cleanup, xe);
> > > +}
> > > +
> > > +void xe_vram_free_memtest_bos(struct xe_device *xe)
> > > +{
> > > +       struct xe_tile *tile;
> > > +       u8 id;
> > > +
> > > +       for_each_tile(tile, xe, id) {
> > > +               if (tile->mem.memtest_bo) {
> > > +                       xe_bo_unpin_map_no_vm(tile->mem.memtest_bo);
> > > +                       tile->mem.memtest_bo = NULL;
> > > +               }
> > > +       }
> > > +}
> > > +
> > > +int xe_vram_memtest(struct xe_device *xe)
> > > +{
> > > +       struct xe_tile *tile;
> > > +       u8 id;
> > > +       int err = 0;
> > > +
> > > +       if (IS_SRIOV_VF(xe))
> > > +               return 0;
> > > +
> > > +       for_each_tile(tile, xe, id) {
> > > +               struct xe_bo *last_page_bo = tile->mem.memtest_bo;
> > > +               struct dma_fence *fence;
> > > +               bool overlap = false;
> > > +               int i;
> > > +               u8 val;
> > > +
> > > +               if (!last_page_bo || !tile->migrate)
> > > +                       continue;
> > > +
> > > +               drm_info(&xe->drm, "Tile %d: Running VRAM
> > > memtest...\n", id);
> > > +
> > > +               /* CPU write and readback first and last byte of the
> > > last page */
> > > +               xe_map_wr(xe, &last_page_bo->vmap, 0, u8, 0xA5);
> > > +               xe_map_wr(xe, &last_page_bo->vmap, SZ_64K - 1, u8,
> > > 0x5A);
> > > +
> > > +               val = xe_map_rd(xe, &last_page_bo->vmap, 0, u8);
> > > +               if (drm_WARN(&xe->drm, val != 0xA5,
> > > +                            "Tile %d: CPU memtest failed at offset 0
> > > (expected 0xA5, got 0x%02x)\n",
> > > +                            id, val)) {
> > > +                       err = -EIO;
> > > +                       goto unpin;
> > > +               }
> > > +
> > > +               val = xe_map_rd(xe, &last_page_bo->vmap, SZ_64K - 1,
> > > u8);
> > > +               if (drm_WARN(&xe->drm, val != 0x5A,
> > > +                            "Tile %d: CPU memtest failed at offset
> > > 65535 (expected 0x5A, got 0x%02x)\n",
> > > +                            id, val)) {
> > > +                       err = -EIO;
> > > +                       goto unpin;
> > > +               }
> > > +
> > > +               /* Non-CCS access via GPU on the last page */
> > > +               xe_bo_lock(last_page_bo, false);
> > > +               fence = xe_migrate_clear(tile->migrate, last_page_bo,
> > > +                                        last_page_bo->ttm.resource,
> > > +
> > > XE_MIGRATE_CLEAR_FLAG_BO_DATA);
> > > +               xe_bo_unlock(last_page_bo);
> > > +
> > > +               if (!IS_ERR(fence)) {
> > > +                       dma_fence_wait(fence, false);
> > > +                       dma_fence_put(fence);
> > > +               } else {
> > > +                       err = PTR_ERR(fence);
> > > +                       goto unpin;
> > > +               }
> > > +
> > > +               val = xe_map_rd(xe, &last_page_bo->vmap, 0, u8);
> > > +               if (drm_WARN(&xe->drm, val != 0x00,
> > > +                            "Tile %d: GPU memtest clear failed at
> > > offset 0 (expected 0x00, got 0x%02x)\n",
> > > +                            id, val)) {
> > > +                       err = -EIO;
> > > +                       goto unpin;
> > > +               }
> > > +
> > > +               /*
> > > +                * Check for CCS overlap on the root tile.
> > > +                *
> > > +                * TODO: maybe extend if we ever get multi-tile +
> > > CCS. Pay
> > > +                * special attention to the l2 flush below. Currently
> > > that is
> > > +                * hard coded to the root tile.
> > > +                */
> > > +               if (!id && xe_device_has_flat_ccs(xe) &&
> > > +                   GRAPHICS_VERx100(xe) >= 2000) {
> > > +                       struct xe_bo *scratch_bo_before;
> > > +                       struct xe_bo *scratch_bo_after;
> > > +
> > > +                       scratch_bo_before =
> > > xe_bo_create_pin_map_novm(xe, tile, SZ_64K,
> > > +
> > > ttm_bo_type_kernel,
> > > +
> > > XE_BO_FLAG_VRAM_IF_DGFX(tile),
> > > +
> > > false);
> > > +                       if (IS_ERR(scratch_bo_before)) {
> > > +                               err = PTR_ERR(scratch_bo_before);
> > > +                               goto unpin;
> > > +                       }
> > > +
> > > +                       scratch_bo_after =
> > > xe_bo_create_pin_map_novm(xe, tile, SZ_64K,
> > > +
> > > ttm_bo_type_kernel,
> > > +
> > > XE_BO_FLAG_VRAM_IF_DGFX(tile),
> > > +
> > > false);
> > > +                       if (IS_ERR(scratch_bo_after)) {
> > > +                               xe_bo_unpin_map_no_vm(scratch_bo_befo
> > > re);
> > > +                               err = PTR_ERR(scratch_bo_after);
> > > +                               goto unpin;
> > > +                       }
> > > +
> > > +                       /* Save original CCS metadata for PA 0 + */
> > > +                       err = xe_migrate_debug_ccs_overlap(tile-
> > > > migrate, scratch_bo_before, false);
> > > +                       if (err) {
> > > +                               xe_bo_unpin_map_no_vm(scratch_bo_befo
> > > re);
> > > +                               xe_bo_unpin_map_no_vm(scratch_bo_afte
> > > r);
> > > +                               goto unpin;
> > > +                       }
> > > +
> > > +                       /*
> > > +                        * Fill last page. If there is CCS overlap in
> > > the last
> > > +                        * page this will snag the raw CCS storage.
> > > +                        */
> > > +                       xe_map_memset(xe, &last_page_bo->vmap, 0,
> > > 0x5A, SZ_64K);
> > > +                       xe_device_wmb(xe);
> > > +
> > > +                       /*
> > > +                        * Global invalidation. Some BMG SKUs will
> > > cache the BAR
> > > +                        * writes in the GPU side VRAM cache. Make
> > > sure above
> > > +                        * writes are fully flushed out to VRAM, so
> > > this is
> > > +                        * hopefully more well behaved with the CCS
> > > unit, if
> > > +                        * there is indeed CCS overlap with normal
> > > VRAM. Since
> > > +                        * there is a separate CCS cache, the CCS
> > > unit might not
> > > +                        * respect the GPU VRAM cache for CCS
> > > accesses, so opt
> > > +                        * for being super careful here.
> > > +                        */
> > > +                       xe_device_l2_flush(xe, true);
> > > +
> > > +                       /* Use GPU to clear CCS state for PA 0 */
> > > +                       xe_map_memset(xe, &scratch_bo_after->vmap, 0,
> > > 0x00, SZ_64K);
> > > +                       err = xe_migrate_debug_ccs_overlap(tile-
> > > > migrate, scratch_bo_after, true);
> > > +                       if (err) {
> > > +                               xe_bo_unpin_map_no_vm(scratch_bo_befo
> > > re);
> > > +                               xe_bo_unpin_map_no_vm(scratch_bo_afte
> > > r);
> > > +                               goto unpin;
> > > +                       }
> > > +                       /*
> > > +                        * Global invalidation. Ensure CCS caches
> > > really are
> > > +                        * nuked and the raw CCS data is visible in
> > > VRAM, for
> > > +                        * the below access.
> > > +                        */
> > > +                       xe_device_l2_flush(xe, true);
> > > +
> > > +                       /* Check if last_page_bo was corrupted by the
> > > GPU CCS clear */
> > > +                       for (i = 0; i < SZ_64K; i += 8) {
> > > +                               u64 payload = xe_map_rd(xe,
> > > &last_page_bo->vmap, i, u64);
> > > +
> > > +                               if (payload != 0x5A5A5A5A5A5A5A5AULL)
> > > {
> > > +                                       overlap = true;
> > > +                                       break;
> > > +                               }
> > > +                       }
> > > +
> > > +                       /* Restore original CCS metadata for PA 0 +
> > > */
> > > +                       err = xe_migrate_debug_ccs_overlap(tile-
> > > > migrate, scratch_bo_before, true);
> > > +                       if (err)
> > > +                               drm_warn(&xe->drm, "Failed to restore
> > > CCS metadata\n");
> > > +
> > > +                       xe_bo_unpin_map_no_vm(scratch_bo_before);
> > > +                       xe_bo_unpin_map_no_vm(scratch_bo_after);
> > > +               }
> > > +
> > > +               if (drm_WARN(&xe->drm, overlap,
> > > +                            "Tile %d: VRAM bounds overlap CCS
> > > region! VRAM sizing is incorrect.\n",
> > > +                            id)) {
> > > +                       err = -EINVAL;
> > > +                       goto unpin;
> > > +               }
> > > +
> > > +               drm_info(&xe->drm, "Tile %d: VRAM memtest
> > > completed.\n", id);
> > > +
> > > +unpin:
> > > +               if (err)
> > > +                       break;
> > > +       }
> > > +
> > > +       xe_vram_free_memtest_bos(xe);
> > > +
> > > +       return err;
> > > +}
> > > +#endif
> > > diff --git a/drivers/gpu/drm/xe/xe_vram.h
> > > b/drivers/gpu/drm/xe/xe_vram.h
> > > index dd1c8bf17922..38425d81f777 100644
> > > --- a/drivers/gpu/drm/xe/xe_vram.h
> > > +++ b/drivers/gpu/drm/xe/xe_vram.h
> > > @@ -23,4 +23,14 @@ resource_size_t xe_vram_region_dpa_base(const
> > > struct xe_vram_region *vram);
> > >   resource_size_t xe_vram_region_usable_size(const struct
> > > xe_vram_region *vram);
> > >   resource_size_t xe_vram_region_actual_physical_size(const struct
> > > xe_vram_region *vram);
> > > +#if IS_ENABLED(CONFIG_DRM_XE_DEBUG_MEM)
> > > +int xe_vram_reserve_memtest_bo(struct xe_device *xe);
> > > +void xe_vram_free_memtest_bos(struct xe_device *xe);
> > > +int xe_vram_memtest(struct xe_device *xe);
> > > +#else
> > > +static inline int xe_vram_reserve_memtest_bo(struct xe_device *xe) {
> > > return 0; }
> > > +static inline void xe_vram_free_memtest_bos(struct xe_device *xe) {}
> > > +static inline int xe_vram_memtest(struct xe_device *xe) { return 0;
> > > }
> > > +#endif
> > > +
> > >   #endif
> > 
>