Re: [PATCH v7 08/12] drm/xe/bo: Block mmap of DONTNEED/purged BOs

Yadav, Arvind
2026-03-26T02:49:43Z

On 26-03-2026 07:03, Matthew Brost wrote:
> On Mon, Mar 23, 2026 at 03:00:57PM +0530, Arvind Yadav wrote:
>> 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)
>>
>> 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 | 26 ++++++++++++++++++++++++--
>> 1 file changed, 24 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
>> index da18b43650e3..83a1d1ca6cc6 100644
>> --- a/drivers/gpu/drm/xe/xe_bo.c
>> +++ b/drivers/gpu/drm/xe/xe_bo.c
>> @@ -2165,10 +2165,32 @@ 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.
>> + */
>> + xe_bo_lock(bo, true);
> You need to check the return of xe_bo_lock if the 2nd argument is true
> as it can fail. On failure, kick the error code to the caller.

Noted,

>
>> + 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,
>> };
>> @@ -3427,8 +3449,8 @@ int xe_gem_mmap_offset_ioctl(struct drm_device *dev, void *data,
>>
>> /* The mmap offset was set up at BO allocation time. */
>> args->offset = drm_vma_node_offset_addr(&gem_obj->vma_node);
>> + drm_gem_object_put(gem_obj);
>>
>> - xe_bo_put(gem_to_xe_bo(gem_obj));
> Look unrelated.

Yes, I will revert back this changes.

Thanks,
Arvind

> Matt
>
>> return 0;
>> }
>>
>> --
>> 2.43.0
>>