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drm/xe: Hold a dma-buf reference for imported BOs

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An imported dma-buf BO is created as a ttm_bo_type_sg BO whose
reservation object is the exporter's dma_buf->resv. The importer,
however, only takes a dma-buf reference after a successful
dma_buf_dynamic_attach(). Until then nothing keeps the exporter alive,
so if the exporter is freed while the BO still references its resv, a
later access to that resv is a use-after-free:

  Oops: general protection fault, probably for non-canonical address
        0x6b6b6b6b6b6b6b9c
  Workqueue: ttm ttm_bo_delayed_delete [ttm]
  RIP: 0010:mutex_can_spin_on_owner+0x3f/0xc0

This can be reached on two paths:

 - dma_buf_dynamic_attach() fails, or
 - ttm_bo_init_reserved() fails during BO creation.

In both cases the BO already has bo->base.resv pointing at the exporter
resv, and sg BOs are always torn down via ttm_bo_delayed_delete(), which
locks bo->base.resv asynchronously - potentially after the exporter has
been freed.

Take the dma-buf reference in xe_bo_init_locked(), before
ttm_bo_init_reserved(), so it also covers a creation failure there, and
release it in xe_ttm_bo_destroy(). The reference is held for the whole
BO lifetime, keeping the shared resv alive on every path.

v2:
  - Reworked the fix to avoid creating the imported sg BO before
    dma_buf_dynamic_attach() succeeds.
  - Attach with importer_priv == NULL and make invalidate_mappings ignore
    incomplete imports.

v3:
  - Dropped the xe-side reordering approach since importer_priv must be
    valid when dma_buf_dynamic_attach() publishes the attachment.
  - Per Christian's suggestion on the v1 thread, keyed the check on
    import_attach rather than removing the sg guard entirely.
  - Fixes both xe and amdgpu in a single TTM patch.

v4:
  - Moved import_attach check to after dma_resv_copy_fences() so fences
    are copied before returning for successful imports (Thomas).
  - Removed exporter-alive claim from commit message (Thomas).

v5:
  - Add drm/xe patch to keep imported sg BOs off the LRU before attach
    succeeds; the TTM fix alone is not sufficient for xe if the BO is
    already LRU-visible. (Thomas)
    v4 patch:
    https://patchwork.freedesktop.org/patch/736663/?series=169129&rev=2
  - Patch 1 (drm/ttm) carries Christian's Reviewed-by from v4.

v6:
  - Reworked the fix based on Thomas' suggestion. Instead of the TTM resv
    individualization (v1-v5) plus the xe off-LRU/placement handling (v5),
    just hold a dma-buf reference for the imported BO lifetime so the
    shared resv can never be freed while the BO still references it.
    Single xe patch, no TTM change. (Thomas)
  - Take the reference in xe_bo_init_locked() before ttm_bo_init_reserved()
    so a TTM creation failure is covered too (Thomas).
  - Dropped the v5 series (drm/ttm + drm/xe off-LRU); the off-LRU approach
    also regressed in CI BAT via ttm_bo_pipeline_gutting() creating a ghost
    BO that outlived the exporter.
    Link to v5: https://patchwork.freedesktop.org/series/169984/

v7:
  - Move changelog above --- so it stays in the commit message.
  - Reorder changelog entries oldest-to-newest. (Thomas)

Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/work_items/8023
Fixes: dd08ebf6c3 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: stable@vger.kernel.org
Cc: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Cc: Christian Konig <christian.koenig@amd.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Suggested-by: Thomas Hellstrom <thomas.hellstrom@linux.intel.com>
Assisted-by: GitHub_Copilot:claude-sonnet-4.6
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Nitin Gote <nitin.r.gote@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patch.msgid.link/20260710191027.260160-2-nitin.r.gote@intel.com
(cherry picked from commit 3516f3fae6be35642f8f06f8a218da6425c0306a)
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
This commit is contained in:
Nitin Gote 2026-07-11 00:40:28 +05:30 committed by Thomas Hellström
parent 7bc597ce74
commit 62775525a2
4 changed files with 25 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
drivers/gpu/drm/xe/xe_bo.c
View File

@ -1349,7 +1349,7 @@ int xe_bo_notifier_prepare_pinned(struct xe_bo *bo)
backup = xe_bo_init_locked(xe, NULL, NULL, bo->ttm.base.resv, NULL, xe_bo_size(bo),
DRM_XE_GEM_CPU_CACHING_WB, ttm_bo_type_kernel,
XE_BO_FLAG_SYSTEM | XE_BO_FLAG_NEEDS_CPU_ACCESS |
XE_BO_FLAG_PINNED, &exec);
XE_BO_FLAG_PINNED, NULL, &exec);
if (IS_ERR(backup)) {
drm_exec_retry_on_contention(&exec);
ret = PTR_ERR(backup);
@ -1490,7 +1490,7 @@ int xe_bo_evict_pinned(struct xe_bo *bo)
xe_bo_size(bo),
DRM_XE_GEM_CPU_CACHING_WB, ttm_bo_type_kernel,
XE_BO_FLAG_SYSTEM | XE_BO_FLAG_NEEDS_CPU_ACCESS |
XE_BO_FLAG_PINNED, &exec);
XE_BO_FLAG_PINNED, NULL, &exec);
if (IS_ERR(backup)) {
drm_exec_retry_on_contention(&exec);
ret = PTR_ERR(backup);
@ -1826,6 +1826,8 @@ static void xe_ttm_bo_destroy(struct ttm_buffer_object *ttm_bo)
if (bo->ttm.base.import_attach)
drm_prime_gem_destroy(&bo->ttm.base, NULL);
if (bo->dma_buf)
dma_buf_put(bo->dma_buf);
drm_gem_object_release(&bo->ttm.base);
xe_assert(xe, list_empty(&ttm_bo->base.gpuva.list));
@ -2283,6 +2285,8 @@ void xe_bo_free(struct xe_bo *bo)
* @cpu_caching: The cpu caching used for system memory backing store.
* @type: The TTM buffer object type.
* @flags: XE_BO_FLAG_ flags.
* @dma_buf: The dma-buf to reference for the BO lifetime (imported BOs),
* or NULL.
* @exec: The drm_exec transaction to use for exhaustive eviction.
*
* Initialize or create an xe buffer object. On failure, any allocated buffer
@ -2294,7 +2298,8 @@ struct xe_bo *xe_bo_init_locked(struct xe_device *xe, struct xe_bo *bo,
struct xe_tile *tile, struct dma_resv *resv,
struct ttm_lru_bulk_move *bulk, size_t size,
u16 cpu_caching, enum ttm_bo_type type,
u32 flags, struct drm_exec *exec)
u32 flags, struct dma_buf *dma_buf,
struct drm_exec *exec)
{
struct ttm_operation_ctx ctx = {
.interruptible = true,
@ -2383,6 +2388,17 @@ struct xe_bo *xe_bo_init_locked(struct xe_device *xe, struct xe_bo *bo,
placement = (type == ttm_bo_type_sg ||
bo->flags & XE_BO_FLAG_DEFER_BACKING) ? &sys_placement :
&bo->placement;
/*
* For imported BOs, keep the exporter dma-buf alive for the BO
* lifetime. Taken before ttm_bo_init_reserved() to also cover a
* creation failure there. Released in xe_ttm_bo_destroy().
*/
if (dma_buf) {
get_dma_buf(dma_buf);
bo->dma_buf = dma_buf;
}
err = ttm_bo_init_reserved(&xe->ttm, &bo->ttm, type,
placement, alignment,
&ctx, NULL, resv, xe_ttm_bo_destroy);
@ -2500,7 +2516,7 @@ __xe_bo_create_locked(struct xe_device *xe,
vm && !xe_vm_in_fault_mode(vm) &&
flags & XE_BO_FLAG_USER ?
&vm->lru_bulk_move : NULL, size,
cpu_caching, type, flags, exec);
cpu_caching, type, flags, NULL, exec);
if (IS_ERR(bo))
return bo;

3
drivers/gpu/drm/xe/xe_bo.h
View File

@ -118,7 +118,8 @@ struct xe_bo *xe_bo_init_locked(struct xe_device *xe, struct xe_bo *bo,
struct xe_tile *tile, struct dma_resv *resv,
struct ttm_lru_bulk_move *bulk, size_t size,
u16 cpu_caching, enum ttm_bo_type type,
u32 flags, struct drm_exec *exec);
u32 flags, struct dma_buf *dma_buf,
struct drm_exec *exec);
struct xe_bo *xe_bo_create_locked(struct xe_device *xe, struct xe_tile *tile,
struct xe_vm *vm, size_t size,
enum ttm_bo_type type, u32 flags,

2
drivers/gpu/drm/xe/xe_bo_types.h
View File

@ -36,6 +36,8 @@ struct xe_bo {
struct xe_bo *backup_obj;
/** @parent_obj: Ref to parent bo if this a backup_obj */
struct xe_bo *parent_obj;
/** @dma_buf: Imported dma-buf ref to keep its resv alive. */
struct dma_buf *dma_buf;
/** @flags: flags for this buffer object */
u32 flags;
/** @vm: VM this BO is attached to, for extobj this will be NULL */

2
drivers/gpu/drm/xe/xe_dma_buf.c
View File

@ -302,7 +302,7 @@ xe_dma_buf_create_obj(struct drm_device *dev, struct dma_buf *dma_buf)
bo = xe_bo_init_locked(xe, NULL, NULL, resv, NULL, dma_buf->size,
0, /* Will require 1way or 2way for vm_bind */
ttm_bo_type_sg, XE_BO_FLAG_SYSTEM, &exec);
ttm_bo_type_sg, XE_BO_FLAG_SYSTEM, dma_buf, &exec);
drm_exec_retry_on_contention(&exec);
if (IS_ERR(bo)) {
ret = PTR_ERR(bo);