[PATCH v8 08/12] drm/xe/bo: Block mmap of DONTNEED/purged BOs

[Arvind Yadav <arvind.yadav@intel.com>]

Don't allow new CPU mmaps to BOs marked DONTNEED or PURGED.
DONTNEED BOs can have their contents discarded at any time, making
CPU access undefined behavior. PURGED BOs have no backing store and
are permanently invalid.

Return -EBUSY for DONTNEED BOs (temporary purgeable state) and
-EINVAL for purged BOs (permanent, no backing store).

The mmap offset ioctl now checks the BO's purgeable state before
allowing userspace to establish a new CPU mapping. This prevents
the race where userspace gets a valid offset but the BO is purged
before actual faulting begins.

Existing mmaps (established before DONTNEED) may still work until
pages are purged, at which point CPU faults fail with SIGBUS.

v6:
- Split DONTNEED → -EBUSY and PURGED → -EINVAL for consistency
  with the rest of the series (Thomas, Matt)

v7:
  - Move purgeable check from xe_gem_mmap_offset_ioctl() into a new
    xe_gem_object_mmap() callback that wraps drm_gem_ttm_mmap(). (Thomas)
  - Use an interruptible lock. (Thomas)

v8:
  - Check xe_bo_lock() return value and propagate error. (Thomas and
    Matt)

Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Himal Prasad Ghimiray <himal.prasad.ghimiray@intel.com>
Signed-off-by: Arvind Yadav <arvind.yadav@intel.com>
---
 drivers/gpu/drm/xe/xe_bo.c | 27 ++++++++++++++++++++++++++-
 1 file changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
index da18b43650e3..c8e3a3fd4880 100644
--- a/drivers/gpu/drm/xe/xe_bo.c
+++ b/drivers/gpu/drm/xe/xe_bo.c
@@ -2165,10 +2165,35 @@ static const struct vm_operations_struct xe_gem_vm_ops = {
 	.access = xe_bo_vm_access,
 };
 
+static int xe_gem_object_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
+{
+	struct xe_bo *bo = gem_to_xe_bo(obj);
+	int err = 0;
+
+	/*
+	 * Reject mmap of purgeable BOs. DONTNEED BOs can be purged
+	 * at any time, making CPU access undefined behavior. Purged BOs have
+	 * no backing store and are permanently invalid.
+	 */
+	err = xe_bo_lock(bo, true);
+	if (err)
+		return err;
+
+	if (xe_bo_madv_is_dontneed(bo))
+		err = -EBUSY;
+	else if (xe_bo_is_purged(bo))
+		err = -EINVAL;
+	xe_bo_unlock(bo);
+	if (err)
+		return err;
+
+	return drm_gem_ttm_mmap(obj, vma);
+}
+
 static const struct drm_gem_object_funcs xe_gem_object_funcs = {
 	.free = xe_gem_object_free,
 	.close = xe_gem_object_close,
-	.mmap = drm_gem_ttm_mmap,
+	.mmap = xe_gem_object_mmap,
 	.export = xe_gem_prime_export,
 	.vm_ops = &xe_gem_vm_ops,
 };
-- 
2.43.0