[PATCH 3/5] drm/xe/bo: Add a bo remove callback

[Thomas Hellström]

On Mon, 2025-03-17 at 15:58 +0000, Matthew Auld wrote:
> On 17/03/2025 10:41, Thomas Hellström wrote:
> > On device unbind, migrate exported bos, including pagemap bos to
> > system. This allows importers to take proper action without
> > disruption. In particular, SVM clients on remote devices may
> > continue as if nothing happened, and can chose a different
> > placement.
> > 
> > The evict_flags() placement is chosen in such a way that bos that
> > aren't exported are purged.
> > 
> > Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
> 
> > ---
> >   drivers/gpu/drm/xe/xe_bo.c     | 96
> > +++++++++++++++++++++++++++++++++-
> >   drivers/gpu/drm/xe/xe_bo.h     |  2 +
> >   drivers/gpu/drm/xe/xe_device.c |  2 +
> >   3 files changed, 99 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/xe/xe_bo.c
> > b/drivers/gpu/drm/xe/xe_bo.c
> > index 64f9c936eea0..c7c206041632 100644
> > --- a/drivers/gpu/drm/xe/xe_bo.c
> > +++ b/drivers/gpu/drm/xe/xe_bo.c
> > @@ -55,6 +55,8 @@ static struct ttm_placement sys_placement = {
> >   	.placement = &sys_placement_flags,
> >   };
> >   
> > +static struct ttm_placement purge_placement;
> > +
> >   static const struct ttm_place tt_placement_flags[] = {
> >   	{
> >   		.fpfn = 0,
> > @@ -281,6 +283,8 @@ int xe_bo_placement_for_flags(struct xe_device
> > *xe, struct xe_bo *bo,
> >   static void xe_evict_flags(struct ttm_buffer_object *tbo,
> >   			   struct ttm_placement *placement)
> >   {
> > +	struct xe_device *xe = container_of(tbo->bdev,
> > typeof(*xe), ttm);
> > +	bool device_unplugged = drm_dev_is_unplugged(&xe->drm);
> >   	struct xe_bo *bo;
> >   
> >   	if (!xe_bo_is_xe_bo(tbo)) {
> > @@ -290,7 +294,7 @@ static void xe_evict_flags(struct
> > ttm_buffer_object *tbo,
> >   			return;
> >   		}
> >   
> > -		*placement = sys_placement;
> > +		*placement = device_unplugged ? purge_placement :
> > sys_placement;
> >   		return;
> >   	}
> >   
> > @@ -300,6 +304,11 @@ static void xe_evict_flags(struct
> > ttm_buffer_object *tbo,
> >   		return;
> >   	}
> >   
> > +	if (device_unplugged && !tbo->base.dma_buf) {
> > +		*placement = purge_placement;
> > +		return;
> > +	}
> 
> > +
> >   	/*
> >   	 * For xe, sg bos that are evicted to system just triggers
> > a
> >   	 * rebind of the sg list upon subsequent validation to
> > XE_PL_TT.
> > @@ -657,11 +666,20 @@ static int xe_bo_move_dmabuf(struct
> > ttm_buffer_object *ttm_bo,
> >   	struct xe_ttm_tt *xe_tt = container_of(ttm_bo->ttm, struct
> > xe_ttm_tt,
> >   					       ttm);
> >   	struct xe_device *xe = ttm_to_xe_device(ttm_bo->bdev);
> > +	bool device_unplugged = drm_dev_is_unplugged(&xe->drm);
> >   	struct sg_table *sg;
> >   
> >   	xe_assert(xe, attach);
> >   	xe_assert(xe, ttm_bo->ttm);
> >   
> > +	if (device_unplugged && new_res->mem_type == XE_PL_SYSTEM
> > &&
> > +	    ttm_bo->sg) {
> > +		dma_resv_wait_timeout(ttm_bo->base.resv,
> > DMA_RESV_USAGE_BOOKKEEP,
> > +				      false,
> > MAX_SCHEDULE_TIMEOUT);
> > +		dma_buf_unmap_attachment(attach, ttm_bo->sg,
> > DMA_BIDIRECTIONAL);
> > +		ttm_bo->sg = NULL;
> > +	}
> 
> > +
> >   	if (new_res->mem_type == XE_PL_SYSTEM)
> >   		goto out;
> >   
> > @@ -2945,6 +2963,82 @@ void
> > xe_bo_runtime_pm_release_mmap_offset(struct xe_bo *bo)
> >   	list_del_init(&bo->vram_userfault_link);
> >   }
> >   
> > +static void xe_bo_dma_unmap_pinned(struct xe_device *xe)
> 
> Should we prefix this with xe_device_ or something?
> xe_device_unmap_pinned_bo() ?

Hmm, yes, while it doesn't take a bo as argument, I think it should
reside in the bo subsystem. Let me check whether we should split this
up and have the loops elsewhere.

> 
> > +{
> > +	struct list_head still_in_list;
> > +
> > +	INIT_LIST_HEAD(&still_in_list);
> 
> LIST_HEAD(still_in_list);

Right. Will fix.
> 
> 
> > +	spin_lock(&xe->pinned.lock);
> > +	for (;;) {
> > +		struct xe_bo *bo = list_first_entry_or_null(&xe-
> > >pinned.kernel_bo_present,
> > +							   
> > typeof(*bo), pinned_link);
> > +		struct ttm_buffer_object *ttm_bo;
> > +		struct ttm_tt *tt;
> > +		struct xe_ttm_tt *xe_tt;
> > +
> > +		if (!bo)
> > +			break;
> > +
> > +		list_move_tail(&bo->pinned_link, &still_in_list);
> > +		xe_bo_get(bo);
> > +		spin_unlock(&xe->pinned.lock);
> > +
> > +		xe_bo_lock(bo, false);
> > +		ttm_bo = &bo->ttm;
> > +		tt = ttm_bo->ttm;
> > +		if (tt) {
> > +			xe_ttm_bo_delete_mem_notify(ttm_bo);
> 
> Do we actually need this?

It's for imported pinned dma-bufs, I don't think we have any of these
ATM, but might in the future I guess. OFC I can structure that a bit
nicer.

> 
> > +			xe_tt = container_of(tt, typeof(*xe_tt),
> > ttm);
> > +			if (xe_tt->sg) {
> > +				dma_unmap_sgtable(xe_tt->xe-
> > >drm.dev, xe_tt->sg,
> > +						 
> > DMA_BIDIRECTIONAL, 0);
> > +				sg_free_table(xe_tt->sg);
> > +				xe_tt->sg = NULL;
> > +			}
> 
> Would it make sense to also call ttm_tt_unpopulate() here, so we nuke
> the pages?

I think we arrived at not nuking the pages for exported dma-bufs. For
the other use-cases I guess it's hard to tell: Is there a chance that
whatever needed the buffer pinned can issue a stray write?

I still think the best approach would to ensure that those subsystems
used devm_ managed resources rather than drmm_-managed resources.
Meanwhile, I can perhaps add a comment about that?

> 
> > +		}
> > +
> > +		xe_bo_unlock(bo);
> > +		xe_bo_put(bo);
> > +		spin_lock(&xe->pinned.lock);
> > +	}
> > +	list_splice_tail(&still_in_list, &xe-
> > >pinned.kernel_bo_present);
> > +	spin_unlock(&xe->pinned.lock);
> > +}
> 
> We could potentially move this type of thing into xe_bo_evict.c?

Could perhaps be the best choice, actually.

> 
> > +
> > +/**
> > + * xe_bo_remove() - Handle bos when the pci_device is about to be
> > removed
> > + * @xe: The xe device.
> > + *
> > + * On pci_device removal we need to drop all dma mappings and move
> > + * the data of exported bos out to system. This includes SVM bos
> > and
> > + * exported dma-buf bos. This is done by evicting all bos, but
> > + * the evict placement in xe_evict_flags() is chosen such that all
> > + * bos except those mentioned are purged, and thus their memory
> > + * is released.
> > + *
> > + * For pinned bos, we're unmapping dma.
> > + */
> > +void xe_bo_remove(struct xe_device *xe)
> 
> xe_device_remove_bo() ?

Will look into it.

> 
> > +{
> > +	unsigned int mem_type;
> > +
> > +	/*
> > +	 * Move pagemap bos and exported dma-buf to system.
> 
> ..and purge everything else."

Will add.

Thanks for reviewing!
/Thomas