Re: [PATCH v1] drm/xe: Drop dma mappings for wedged device

[Matthew Auld <matthew.auld@intel.com>]

On 24/03/2026 15:14, Raag Jadav wrote:
> On Tue, Mar 24, 2026 at 12:52:30PM +0000, Matthew Auld wrote:
>> On 24/03/2026 07:13, Raag Jadav wrote:
>>> As per uapi documentation[1], the prerequisite for wedged device is to
>>> drop all dma mappings. Reuse xe_bo_pci_dev_remove_pinned() for this,
>>> which iterates over external bo list and removes all dma mappings.
>>>
>>> [1] Documentation/gpu/drm-uapi.rst
>>
>> Can you point to where it says that? Do you just mean the: "disabling DMA to
>> system memory" ?
>>
>> One other thing that maybe jumps out is:
>>
>> "All existing mmaps should be invalidated and
>> page faults should be redirected to a dummy page"
>>
>> Are we also missing that? We have the dummy page flow, but do we actually
>> force everything to be refaulted?
> 
> I tried this with commit c020fff70d75 but it clearly doesn't cover
> everything.

Ah right. Yeah, in theory if you do something like:

addr = mmap(bo);
addr[0] = 0xdeadbeaf;
igt_assert_eq(addr[0], 0xdeadbeaf);
wedge();
igt_assert_eq(addr[0], 0);

It should fail the second assert, I think. With the below fix in theory 
the access after the wedge will now trigger a new fault which will then 
map your dummy page (which is hopefully all zeroes), which I think is 
what the doc wants.

> 
>> Something like:
>>
>>   /* Clear all CPU mappings pointing to this device */
>>   unmap_mapping_range(dev->anon_inode->i_mapping, 0, 0, 1);
> 
> Sure.
> 
>>> Signed-off-by: Raag Jadav <raag.jadav@intel.com>
>>> ---
>>> PS: This is pretty much uncharted territory for me, so please consider
>>> this an RFC.
>>>
>>>    drivers/gpu/drm/xe/xe_bo_evict.c | 8 +++++++-
>>>    drivers/gpu/drm/xe/xe_bo_evict.h | 1 +
>>>    drivers/gpu/drm/xe/xe_device.c   | 2 ++
>>>    3 files changed, 10 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_bo_evict.c b/drivers/gpu/drm/xe/xe_bo_evict.c
>>> index 7661fca7f278..f741cda50b2d 100644
>>> --- a/drivers/gpu/drm/xe/xe_bo_evict.c
>>> +++ b/drivers/gpu/drm/xe/xe_bo_evict.c
>>> @@ -270,7 +270,13 @@ int xe_bo_restore_late(struct xe_device *xe)
>>>    	return ret;
>>>    }
>>> -static void xe_bo_pci_dev_remove_pinned(struct xe_device *xe)
>>> +/**
>>> + * xe_bo_pci_dev_remove_pinned() - Unmap external bos
>>> + * @xe: xe device
>>> + *
>>> + * Drop dma mappings of all external pinned bos.
>>> + */
>>> +void xe_bo_pci_dev_remove_pinned(struct xe_device *xe)
>>>    {
>>>    	struct xe_tile *tile;
>>>    	unsigned int id;
>>> diff --git a/drivers/gpu/drm/xe/xe_bo_evict.h b/drivers/gpu/drm/xe/xe_bo_evict.h
>>> index e8385cb7f5e9..6ce27e272780 100644
>>> --- a/drivers/gpu/drm/xe/xe_bo_evict.h
>>> +++ b/drivers/gpu/drm/xe/xe_bo_evict.h
>>> @@ -15,6 +15,7 @@ void xe_bo_notifier_unprepare_all_pinned(struct xe_device *xe);
>>>    int xe_bo_restore_early(struct xe_device *xe);
>>>    int xe_bo_restore_late(struct xe_device *xe);
>>> +void xe_bo_pci_dev_remove_pinned(struct xe_device *xe);
>>>    void xe_bo_pci_dev_remove_all(struct xe_device *xe);
>>>    int xe_bo_pinned_init(struct xe_device *xe);
>>> diff --git a/drivers/gpu/drm/xe/xe_device.c b/drivers/gpu/drm/xe/xe_device.c
>>> index 207ad2eea412..ac51b04560df 100644
>>> --- a/drivers/gpu/drm/xe/xe_device.c
>>> +++ b/drivers/gpu/drm/xe/xe_device.c
>>> @@ -1351,6 +1351,8 @@ void xe_device_declare_wedged(struct xe_device *xe)
>>>    	for_each_gt(gt, xe, id)
>>>    		xe_gt_declare_wedged(gt);
>>> +	xe_bo_pci_dev_remove_pinned(xe);
>>
>> AFAIK this just removes the iommu mappings for kernel BOs (small subset of
>> BOs), if there are any. Also if you are not using iommu, then dma between
>> GPU and system memory is still possible. And for userspace BOs nothing
>> changes. But I guess this is still better than nothing and will maybe catch
>> some misuse?
> 
> Yeah, I just floated this to start the discussion. Thanks for the pointers,
> will explore this.
> 
> Raag
> 
>>>    	if (xe_device_wedged(xe)) {
>>>    		/*
>>>    		 * XE_WEDGED_MODE_UPON_ANY_HANG_NO_RESET is intended for debugging
>>