Hi, Tvrtko
On Mon, 2021-11-01 at 13:14 +0000, Tvrtko Ursulin wrote:
>
> On 01/11/2021 12:24, Thomas Hellström wrote:
> > As we start to introduce asynchronous failsafe object migration,
> > where we update the object state and then submit asynchronous
> > commands we need to record what memory resources are actually used
> > by various part of the command stream. Initially for three
> > purposes:
> >
> > 1) Error capture.
> > 2) Asynchronous migration error recovery.
> > 3) Asynchronous vma bind.
>
> FWIW something like this may be interesting to me as well, although I
> haven't looked much into details yet, for the purpose of allowing
> delayed "put pages" via decoupling from the GEM bo.
> Two questions after glancing over:
>
> 1)
> I do wonder if abstracting "sgt" away from the name would make sense?
> Like perhaps obj->mm.pages being the location of the new abstraction
> so
> naming it along the lines of i915_obj_pages or something.
Well it's not yet clear how this will end up. Really this should
develop into something along the lines of "struct i915_async_obj", on
which the sg-list is a member only. Depending on how this turns out and
if it remains an sg-list I think your suggestion makes sense, but is it
something we can postpone for now?
>
> 2)
> And how come obj->mm.pages remains? Does it go away later in follow
> up work?
For the non-ttm backends, it's not yet implemented, so once they are
either moved to TTM or updated, we can completely replace obj-
>mm.pages.
/Thomas
>
> Regards,
>
> Tvrtko
>
> > At the time where these happens, the object state may have been
> > updated
> > to be several migrations ahead and object sg-tables discarded.
> >
> > In order to make it possible to keep sg-tables with memory resource
> > information for these operations, introduce refcounted sg-tables
> > that
> > aren't freed until the last user is done with them.
> >
> > The alternative would be to reference information sitting on the
> > corresponding ttm_resources which typically have the same lifetime
> > as
> > these refcountes sg_tables, but that leads to other awkward
> > constructs:
> > Due to the design direction chosen for ttm resource managers that
> > would
> > lead to diamond-style inheritance, the LMEM resources may sometimes
> > be
> > prematurely freed, and finally the subclassed struct ttm_resource
> > would
> > have to bleed into the asynchronous vma bind code.
> >
> > v3:
> > - Address a number of style issues (Matthew Auld)
> > v4:
> > - Dont check for st->sgl being NULL in
> > i915_ttm_tt__shmem_unpopulate(),
> > that should never happen. (Matthew Auld)
> > v5:
> > - Fix a Potential double-free (Matthew Auld)
> >
> > Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> > Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/gem/i915_gem_object.h | 12 +-
> > .../gpu/drm/i915/gem/i915_gem_object_types.h | 3 +-
> > drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 53 +++--
> > drivers/gpu/drm/i915/gem/i915_gem_ttm.c | 186 ++++++++++---
> > -----
> > drivers/gpu/drm/i915/i915_scatterlist.c | 62 ++++--
> > drivers/gpu/drm/i915/i915_scatterlist.h | 76 ++++++-
> > drivers/gpu/drm/i915/intel_region_ttm.c | 15 +-
> > drivers/gpu/drm/i915/intel_region_ttm.h | 5 +-
> > drivers/gpu/drm/i915/selftests/mock_region.c | 12 +-
> > 9 files changed, 277 insertions(+), 147 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > index a5479ac7a4ad..ba224598ed69 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.h
> > @@ -620,12 +620,12 @@ int i915_gem_object_wait_migration(struct
> > drm_i915_gem_object *obj,
> > bool i915_gem_object_placement_possible(struct
> > drm_i915_gem_object *obj,
> > enum intel_memory_type
> > type);
> >
> > -struct sg_table *shmem_alloc_st(struct drm_i915_private *i915,
> > - size_t size, struct
> > intel_memory_region *mr,
> > - struct address_space *mapping,
> > - unsigned int max_segment);
> > -void shmem_free_st(struct sg_table *st, struct address_space
> > *mapping,
> > - bool dirty, bool backup);
> > +int shmem_sg_alloc_table(struct drm_i915_private *i915, struct
> > sg_table *st,
> > + size_t size, struct intel_memory_region
> > *mr,
> > + struct address_space *mapping,
> > + unsigned int max_segment);
> > +void shmem_sg_free_table(struct sg_table *st, struct address_space
> > *mapping,
> > + bool dirty, bool backup);
> > void __shmem_writeback(size_t size, struct address_space
> > *mapping);
> >
> > #ifdef CONFIG_MMU_NOTIFIER
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > index a4b69a43b898..604ed5ad77f5 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_object_types.h
> > @@ -544,6 +544,7 @@ struct drm_i915_gem_object {
> > */
> > struct list_head region_link;
> >
> > + struct i915_refct_sgt *rsgt;
> > struct sg_table *pages;
> > void *mapping;
> >
> > @@ -597,7 +598,7 @@ struct drm_i915_gem_object {
> > } mm;
> >
> > struct {
> > - struct sg_table *cached_io_st;
> > + struct i915_refct_sgt *cached_io_rsgt;
> > struct i915_gem_object_page_iter get_io_page;
> > struct drm_i915_gem_object *backup;
> > bool created:1;
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > index 01f332d8dbde..4a88c89b7a14 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c
> > @@ -25,8 +25,8 @@ static void check_release_pagevec(struct pagevec
> > *pvec)
> > cond_resched();
> > }
> >
> > -void shmem_free_st(struct sg_table *st, struct address_space
> > *mapping,
> > - bool dirty, bool backup)
> > +void shmem_sg_free_table(struct sg_table *st, struct address_space
> > *mapping,
> > + bool dirty, bool backup)
> > {
> > struct sgt_iter sgt_iter;
> > struct pagevec pvec;
> > @@ -49,17 +49,15 @@ void shmem_free_st(struct sg_table *st, struct
> > address_space *mapping,
> > check_release_pagevec(&pvec);
> >
> > sg_free_table(st);
> > - kfree(st);
> > }
> >
> > -struct sg_table *shmem_alloc_st(struct drm_i915_private *i915,
> > - size_t size, struct
> > intel_memory_region *mr,
> > - struct address_space *mapping,
> > - unsigned int max_segment)
> > +int shmem_sg_alloc_table(struct drm_i915_private *i915, struct
> > sg_table *st,
> > + size_t size, struct intel_memory_region
> > *mr,
> > + struct address_space *mapping,
> > + unsigned int max_segment)
> > {
> > const unsigned long page_count = size / PAGE_SIZE;
> > unsigned long i;
> > - struct sg_table *st;
> > struct scatterlist *sg;
> > struct page *page;
> > unsigned long last_pfn = 0; /* suppress gcc warning */
> > @@ -71,16 +69,10 @@ struct sg_table *shmem_alloc_st(struct
> > drm_i915_private *i915,
> > * object, bail early.
> > */
> > if (size > resource_size(&mr->region))
> > - return ERR_PTR(-ENOMEM);
> > -
> > - st = kmalloc(sizeof(*st), GFP_KERNEL);
> > - if (!st)
> > - return ERR_PTR(-ENOMEM);
> > + return -ENOMEM;
> >
> > - if (sg_alloc_table(st, page_count, GFP_KERNEL)) {
> > - kfree(st);
> > - return ERR_PTR(-ENOMEM);
> > - }
> > + if (sg_alloc_table(st, page_count, GFP_KERNEL))
> > + return -ENOMEM;
> >
> > /*
> > * Get the list of pages out of our struct file. They'll
> > be pinned
> > @@ -167,15 +159,14 @@ struct sg_table *shmem_alloc_st(struct
> > drm_i915_private *i915,
> > /* Trim unused sg entries to avoid wasting memory. */
> > i915_sg_trim(st);
> >
> > - return st;
> > + return 0;
> > err_sg:
> > sg_mark_end(sg);
> > if (sg != st->sgl) {
> > - shmem_free_st(st, mapping, false, false);
> > + shmem_sg_free_table(st, mapping, false, false);
> > } else {
> > mapping_clear_unevictable(mapping);
> > sg_free_table(st);
> > - kfree(st);
> > }
> >
> > /*
> > @@ -190,7 +181,7 @@ struct sg_table *shmem_alloc_st(struct
> > drm_i915_private *i915,
> > if (ret == -ENOSPC)
> > ret = -ENOMEM;
> >
> > - return ERR_PTR(ret);
> > + return ret;
> > }
> >
> > static int shmem_get_pages(struct drm_i915_gem_object *obj)
> > @@ -214,11 +205,14 @@ static int shmem_get_pages(struct
> > drm_i915_gem_object *obj)
> > GEM_BUG_ON(obj->write_domain & I915_GEM_GPU_DOMAINS);
> >
> > rebuild_st:
> > - st = shmem_alloc_st(i915, obj->base.size, mem, mapping,
> > max_segment);
> > - if (IS_ERR(st)) {
> > - ret = PTR_ERR(st);
> > + st = kmalloc(sizeof(*st), GFP_KERNEL);
> > + if (!st)
> > + return -ENOMEM;
> > +
> > + ret = shmem_sg_alloc_table(i915, st, obj->base.size, mem,
> > mapping,
> > + max_segment);
> > + if (ret)
> > goto err_st;
> > - }
> >
> > ret = i915_gem_gtt_prepare_pages(obj, st);
> > if (ret) {
> > @@ -254,7 +248,7 @@ static int shmem_get_pages(struct
> > drm_i915_gem_object *obj)
> > return 0;
> >
> > err_pages:
> > - shmem_free_st(st, mapping, false, false);
> > + shmem_sg_free_table(st, mapping, false, false);
> > /*
> > * shmemfs first checks if there is enough memory to
> > allocate the page
> > * and reports ENOSPC should there be insufficient, along
> > with the usual
> > @@ -268,6 +262,8 @@ static int shmem_get_pages(struct
> > drm_i915_gem_object *obj)
> > if (ret == -ENOSPC)
> > ret = -ENOMEM;
> >
> > + kfree(st);
> > +
> > return ret;
> > }
> >
> > @@ -374,8 +370,9 @@ void i915_gem_object_put_pages_shmem(struct
> > drm_i915_gem_object *obj, struct sg_
> > if (i915_gem_object_needs_bit17_swizzle(obj))
> > i915_gem_object_save_bit_17_swizzle(obj, pages);
> >
> > - shmem_free_st(pages, file_inode(obj->base.filp)->i_mapping,
> > - obj->mm.dirty, obj->mm.madv ==
> > I915_MADV_WILLNEED);
> > + shmem_sg_free_table(pages, file_inode(obj->base.filp)-
> > >i_mapping,
> > + obj->mm.dirty, obj->mm.madv ==
> > I915_MADV_WILLNEED);
> > + kfree(pages);
> > obj->mm.dirty = false;
> > }
> >
> > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > index 4fd2edb20dd9..6a05369e2705 100644
> > --- a/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > +++ b/drivers/gpu/drm/i915/gem/i915_gem_ttm.c
> > @@ -34,7 +34,7 @@
> > * struct i915_ttm_tt - TTM page vector with additional private
> > information
> > * @ttm: The base TTM page vector.
> > * @dev: The struct device used for dma mapping and unmapping.
> > - * @cached_st: The cached scatter-gather table.
> > + * @cached_rsgt: The cached scatter-gather table.
> > * @is_shmem: Set if using shmem.
> > * @filp: The shmem file, if using shmem backend.
> > *
> > @@ -47,7 +47,7 @@
> > struct i915_ttm_tt {
> > struct ttm_tt ttm;
> > struct device *dev;
> > - struct sg_table *cached_st;
> > + struct i915_refct_sgt cached_rsgt;
> >
> > bool is_shmem;
> > struct file *filp;
> > @@ -217,18 +217,16 @@ static int i915_ttm_tt_shmem_populate(struct
> > ttm_device *bdev,
> > i915_tt->filp = filp;
> > }
> >
> > - st = shmem_alloc_st(i915, size, mr, filp->f_mapping,
> > max_segment);
> > - if (IS_ERR(st))
> > - return PTR_ERR(st);
> > + st = &i915_tt->cached_rsgt.table;
> > + err = shmem_sg_alloc_table(i915, st, size, mr, filp-
> > >f_mapping,
> > + max_segment);
> > + if (err)
> > + return err;
> >
> > - err = dma_map_sg_attrs(i915_tt->dev,
> > - st->sgl, st->nents,
> > - DMA_BIDIRECTIONAL,
> > - DMA_ATTR_SKIP_CPU_SYNC);
> > - if (err <= 0) {
> > - err = -EINVAL;
> > + err = dma_map_sgtable(i915_tt->dev, st, DMA_BIDIRECTIONAL,
> > + DMA_ATTR_SKIP_CPU_SYNC);
> > + if (err)
> > goto err_free_st;
> > - }
> >
> > i = 0;
> > for_each_sgt_page(page, sgt_iter, st)
> > @@ -237,11 +235,11 @@ static int i915_ttm_tt_shmem_populate(struct
> > ttm_device *bdev,
> > if (ttm->page_flags & TTM_TT_FLAG_SWAPPED)
> > ttm->page_flags &= ~TTM_TT_FLAG_SWAPPED;
> >
> > - i915_tt->cached_st = st;
> > return 0;
> >
> > err_free_st:
> > - shmem_free_st(st, filp->f_mapping, false, false);
> > + shmem_sg_free_table(st, filp->f_mapping, false, false);
> > +
> > return err;
> > }
> >
> > @@ -249,16 +247,27 @@ static void
> > i915_ttm_tt_shmem_unpopulate(struct ttm_tt *ttm)
> > {
> > struct i915_ttm_tt *i915_tt = container_of(ttm,
> > typeof(*i915_tt), ttm);
> > bool backup = ttm->page_flags & TTM_TT_FLAG_SWAPPED;
> > + struct sg_table *st = &i915_tt->cached_rsgt.table;
> > +
> > + shmem_sg_free_table(st, file_inode(i915_tt->filp)-
> > >i_mapping,
> > + backup, backup);
> > +}
> >
> > - dma_unmap_sg(i915_tt->dev, i915_tt->cached_st->sgl,
> > - i915_tt->cached_st->nents,
> > - DMA_BIDIRECTIONAL);
> > +static void i915_ttm_tt_release(struct kref *ref)
> > +{
> > + struct i915_ttm_tt *i915_tt =
> > + container_of(ref, typeof(*i915_tt),
> > cached_rsgt.kref);
> > + struct sg_table *st = &i915_tt->cached_rsgt.table;
> >
> > - shmem_free_st(fetch_and_zero(&i915_tt->cached_st),
> > - file_inode(i915_tt->filp)->i_mapping,
> > - backup, backup);
> > + GEM_WARN_ON(st->sgl);
> > +
> > + kfree(i915_tt);
> > }
> >
> > +static const struct i915_refct_sgt_ops tt_rsgt_ops = {
> > + .release = i915_ttm_tt_release
> > +};
> > +
> > static struct ttm_tt *i915_ttm_tt_create(struct ttm_buffer_object
> > *bo,
> > uint32_t page_flags)
> > {
> > @@ -287,6 +296,9 @@ static struct ttm_tt *i915_ttm_tt_create(struct
> > ttm_buffer_object *bo,
> > if (ret)
> > goto err_free;
> >
> > + __i915_refct_sgt_init(&i915_tt->cached_rsgt, bo->base.size,
> > + &tt_rsgt_ops);
> > +
> > i915_tt->dev = obj->base.dev->dev;
> >
> > return &i915_tt->ttm;
> > @@ -311,17 +323,15 @@ static int i915_ttm_tt_populate(struct
> > ttm_device *bdev,
> > static void i915_ttm_tt_unpopulate(struct ttm_device *bdev,
> > struct ttm_tt *ttm)
> > {
> > struct i915_ttm_tt *i915_tt = container_of(ttm,
> > typeof(*i915_tt), ttm);
> > + struct sg_table *st = &i915_tt->cached_rsgt.table;
> > +
> > + if (st->sgl)
> > + dma_unmap_sgtable(i915_tt->dev, st,
> > DMA_BIDIRECTIONAL, 0);
> >
> > if (i915_tt->is_shmem) {
> > i915_ttm_tt_shmem_unpopulate(ttm);
> > } else {
> > - if (i915_tt->cached_st) {
> > - dma_unmap_sgtable(i915_tt->dev, i915_tt-
> > >cached_st,
> > - DMA_BIDIRECTIONAL, 0);
> > - sg_free_table(i915_tt->cached_st);
> > - kfree(i915_tt->cached_st);
> > - i915_tt->cached_st = NULL;
> > - }
> > + sg_free_table(st);
> > ttm_pool_free(&bdev->pool, ttm);
> > }
> > }
> > @@ -334,7 +344,7 @@ static void i915_ttm_tt_destroy(struct
> > ttm_device *bdev, struct ttm_tt *ttm)
> > fput(i915_tt->filp);
> >
> > ttm_tt_fini(ttm);
> > - kfree(i915_tt);
> > + i915_refct_sgt_put(&i915_tt->cached_rsgt);
> > }
> >
> > static bool i915_ttm_eviction_valuable(struct ttm_buffer_object
> > *bo,
> > @@ -376,12 +386,12 @@ static int i915_ttm_move_notify(struct
> > ttm_buffer_object *bo)
> > return 0;
> > }
> >
> > -static void i915_ttm_free_cached_io_st(struct drm_i915_gem_object
> > *obj)
> > +static void i915_ttm_free_cached_io_rsgt(struct
> > drm_i915_gem_object *obj)
> > {
> > struct radix_tree_iter iter;
> > void __rcu **slot;
> >
> > - if (!obj->ttm.cached_io_st)
> > + if (!obj->ttm.cached_io_rsgt)
> > return;
> >
> > rcu_read_lock();
> > @@ -389,9 +399,8 @@ static void i915_ttm_free_cached_io_st(struct
> > drm_i915_gem_object *obj)
> > radix_tree_delete(&obj->ttm.get_io_page.radix,
> > iter.index);
> > rcu_read_unlock();
> >
> > - sg_free_table(obj->ttm.cached_io_st);
> > - kfree(obj->ttm.cached_io_st);
> > - obj->ttm.cached_io_st = NULL;
> > + i915_refct_sgt_put(obj->ttm.cached_io_rsgt);
> > + obj->ttm.cached_io_rsgt = NULL;
> > }
> >
> > static void
> > @@ -477,7 +486,7 @@ static int i915_ttm_purge(struct
> > drm_i915_gem_object *obj)
> > obj->write_domain = 0;
> > obj->read_domains = 0;
> > i915_ttm_adjust_gem_after_move(obj);
> > - i915_ttm_free_cached_io_st(obj);
> > + i915_ttm_free_cached_io_rsgt(obj);
> > obj->mm.madv = __I915_MADV_PURGED;
> > return 0;
> > }
> > @@ -532,7 +541,7 @@ static void i915_ttm_swap_notify(struct
> > ttm_buffer_object *bo)
> > int ret = i915_ttm_move_notify(bo);
> >
> > GEM_WARN_ON(ret);
> > - GEM_WARN_ON(obj->ttm.cached_io_st);
> > + GEM_WARN_ON(obj->ttm.cached_io_rsgt);
> > if (!ret && obj->mm.madv != I915_MADV_WILLNEED)
> > i915_ttm_purge(obj);
> > }
> > @@ -543,7 +552,7 @@ static void i915_ttm_delete_mem_notify(struct
> > ttm_buffer_object *bo)
> >
> > if (likely(obj)) {
> > __i915_gem_object_pages_fini(obj);
> > - i915_ttm_free_cached_io_st(obj);
> > + i915_ttm_free_cached_io_rsgt(obj);
> > }
> > }
> >
> > @@ -563,40 +572,35 @@ i915_ttm_region(struct ttm_device *bdev, int
> > ttm_mem_type)
> > ttm_mem_type -
> > I915_PL_LMEM0);
> > }
> >
> > -static struct sg_table *i915_ttm_tt_get_st(struct ttm_tt *ttm)
> > +static struct i915_refct_sgt *i915_ttm_tt_get_st(struct ttm_tt
> > *ttm)
> > {
> > struct i915_ttm_tt *i915_tt = container_of(ttm,
> > typeof(*i915_tt), ttm);
> > struct sg_table *st;
> > int ret;
> >
> > - if (i915_tt->cached_st)
> > - return i915_tt->cached_st;
> > -
> > - st = kzalloc(sizeof(*st), GFP_KERNEL);
> > - if (!st)
> > - return ERR_PTR(-ENOMEM);
> > + if (i915_tt->cached_rsgt.table.sgl)
> > + return i915_refct_sgt_get(&i915_tt->cached_rsgt);
> >
> > + st = &i915_tt->cached_rsgt.table;
> > ret = sg_alloc_table_from_pages_segment(st,
> > ttm->pages, ttm->num_pages,
> > 0, (unsigned long)ttm->num_pages <<
> > PAGE_SHIFT,
> > i915_sg_segment_size(), GFP_KERNEL);
> > if (ret) {
> > - kfree(st);
> > + st->sgl = NULL;
> > return ERR_PTR(ret);
> > }
> >
> > ret = dma_map_sgtable(i915_tt->dev, st, DMA_BIDIRECTIONAL,
> > 0);
> > if (ret) {
> > sg_free_table(st);
> > - kfree(st);
> > return ERR_PTR(ret);
> > }
> >
> > - i915_tt->cached_st = st;
> > - return st;
> > + return i915_refct_sgt_get(&i915_tt->cached_rsgt);
> > }
> >
> > -static struct sg_table *
> > +static struct i915_refct_sgt *
> > i915_ttm_resource_get_st(struct drm_i915_gem_object *obj,
> > struct ttm_resource *res)
> > {
> > @@ -610,7 +614,21 @@ i915_ttm_resource_get_st(struct
> > drm_i915_gem_object *obj,
> > * the resulting st. Might make sense for GGTT.
> > */
> > GEM_WARN_ON(!cpu_maps_iomem(res));
> > - return intel_region_ttm_resource_to_st(obj->mm.region,
> > res);
> > + if (bo->resource == res) {
> > + if (!obj->ttm.cached_io_rsgt) {
> > + struct i915_refct_sgt *rsgt;
> > +
> > + rsgt =
> > intel_region_ttm_resource_to_rsgt(obj->mm.region,
> > +
> > res);
> > + if (IS_ERR(rsgt))
> > + return rsgt;
> > +
> > + obj->ttm.cached_io_rsgt = rsgt;
> > + }
> > + return i915_refct_sgt_get(obj->ttm.cached_io_rsgt);
> > + }
> > +
> > + return intel_region_ttm_resource_to_rsgt(obj->mm.region,
> > res);
> > }
> >
> > static int i915_ttm_accel_move(struct ttm_buffer_object *bo,
> > @@ -621,10 +639,7 @@ static int i915_ttm_accel_move(struct
> > ttm_buffer_object *bo,
> > {
> > struct drm_i915_private *i915 = container_of(bo->bdev,
> > typeof(*i915),
> > bdev);
> > - struct ttm_resource_manager *src_man =
> > - ttm_manager_type(bo->bdev, bo->resource->mem_type);
> > struct drm_i915_gem_object *obj = i915_ttm_to_gem(bo);
> > - struct sg_table *src_st;
> > struct i915_request *rq;
> > struct ttm_tt *src_ttm = bo->ttm;
> > enum i915_cache_level src_level, dst_level;
> > @@ -650,17 +665,22 @@ static int i915_ttm_accel_move(struct
> > ttm_buffer_object *bo,
> > }
> > intel_engine_pm_put(i915->gt.migrate.context-
> > >engine);
> > } else {
> > - src_st = src_man->use_tt ?
> > i915_ttm_tt_get_st(src_ttm) :
> > - obj->ttm.cached_io_st;
> > + struct i915_refct_sgt *src_rsgt =
> > + i915_ttm_resource_get_st(obj, bo-
> > >resource);
> > +
> > + if (IS_ERR(src_rsgt))
> > + return PTR_ERR(src_rsgt);
> >
> > src_level = i915_ttm_cache_level(i915, bo-
> > >resource, src_ttm);
> > intel_engine_pm_get(i915->gt.migrate.context-
> > >engine);
> > ret = intel_context_migrate_copy(i915-
> > >gt.migrate.context,
> > - NULL, src_st->sgl,
> > src_level,
> > + NULL, src_rsgt-
> > >table.sgl,
> > + src_level,
> >
> > gpu_binds_iomem(bo->resource),
> > dst_st->sgl,
> > dst_level,
> >
> > gpu_binds_iomem(dst_mem),
> > &rq);
> > + i915_refct_sgt_put(src_rsgt);
> > if (!ret && rq) {
> > i915_request_wait(rq, 0,
> > MAX_SCHEDULE_TIMEOUT);
> > i915_request_put(rq);
> > @@ -674,13 +694,14 @@ static int i915_ttm_accel_move(struct
> > ttm_buffer_object *bo,
> > static void __i915_ttm_move(struct ttm_buffer_object *bo, bool
> > clear,
> > struct ttm_resource *dst_mem,
> > struct ttm_tt *dst_ttm,
> > - struct sg_table *dst_st,
> > + struct i915_refct_sgt *dst_rsgt,
> > bool allow_accel)
> > {
> > int ret = -EINVAL;
> >
> > if (allow_accel)
> > - ret = i915_ttm_accel_move(bo, clear, dst_mem,
> > dst_ttm, dst_st);
> > + ret = i915_ttm_accel_move(bo, clear, dst_mem,
> > dst_ttm,
> > + &dst_rsgt->table);
> > if (ret) {
> > struct drm_i915_gem_object *obj =
> > i915_ttm_to_gem(bo);
> > struct intel_memory_region *dst_reg, *src_reg;
> > @@ -697,12 +718,13 @@ static void __i915_ttm_move(struct
> > ttm_buffer_object *bo, bool clear,
> > dst_iter = !cpu_maps_iomem(dst_mem) ?
> > ttm_kmap_iter_tt_init(&_dst_iter.tt,
> > dst_ttm) :
> > ttm_kmap_iter_iomap_init(&_dst_iter.io,
> > &dst_reg->iomap,
> > - dst_st, dst_reg-
> > >region.start);
> > + &dst_rsgt->table,
> > + dst_reg-
> > >region.start);
> >
> > src_iter = !cpu_maps_iomem(bo->resource) ?
> > ttm_kmap_iter_tt_init(&_src_iter.tt, bo-
> > >ttm) :
> > ttm_kmap_iter_iomap_init(&_src_iter.io,
> > &src_reg->iomap,
> > - obj-
> > >ttm.cached_io_st,
> > + &obj-
> > >ttm.cached_io_rsgt->table,
> > src_reg-
> > >region.start);
> >
> > ttm_move_memcpy(clear, dst_mem->num_pages,
> > dst_iter, src_iter);
> > @@ -718,7 +740,7 @@ static int i915_ttm_move(struct
> > ttm_buffer_object *bo, bool evict,
> > struct ttm_resource_manager *dst_man =
> > ttm_manager_type(bo->bdev, dst_mem->mem_type);
> > struct ttm_tt *ttm = bo->ttm;
> > - struct sg_table *dst_st;
> > + struct i915_refct_sgt *dst_rsgt;
> > bool clear;
> > int ret;
> >
> > @@ -744,22 +766,24 @@ static int i915_ttm_move(struct
> > ttm_buffer_object *bo, bool evict,
> > return ret;
> > }
> >
> > - dst_st = i915_ttm_resource_get_st(obj, dst_mem);
> > - if (IS_ERR(dst_st))
> > - return PTR_ERR(dst_st);
> > + dst_rsgt = i915_ttm_resource_get_st(obj, dst_mem);
> > + if (IS_ERR(dst_rsgt))
> > + return PTR_ERR(dst_rsgt);
> >
> > clear = !cpu_maps_iomem(bo->resource) && (!ttm ||
> > !ttm_tt_is_populated(ttm));
> > if (!(clear && ttm && !(ttm->page_flags &
> > TTM_TT_FLAG_ZERO_ALLOC)))
> > - __i915_ttm_move(bo, clear, dst_mem, bo->ttm,
> > dst_st, true);
> > + __i915_ttm_move(bo, clear, dst_mem, bo->ttm,
> > dst_rsgt, true);
> >
> > ttm_bo_move_sync_cleanup(bo, dst_mem);
> > i915_ttm_adjust_domains_after_move(obj);
> > - i915_ttm_free_cached_io_st(obj);
> > + i915_ttm_free_cached_io_rsgt(obj);
> >
> > if (gpu_binds_iomem(dst_mem) || cpu_maps_iomem(dst_mem)) {
> > - obj->ttm.cached_io_st = dst_st;
> > - obj->ttm.get_io_page.sg_pos = dst_st->sgl;
> > + obj->ttm.cached_io_rsgt = dst_rsgt;
> > + obj->ttm.get_io_page.sg_pos = dst_rsgt->table.sgl;
> > obj->ttm.get_io_page.sg_idx = 0;
> > + } else {
> > + i915_refct_sgt_put(dst_rsgt);
> > }
> >
> > i915_ttm_adjust_lru(obj);
> > @@ -825,7 +849,6 @@ static int __i915_ttm_get_pages(struct
> > drm_i915_gem_object *obj,
> > .interruptible = true,
> > .no_wait_gpu = false,
> > };
> > - struct sg_table *st;
> > int real_num_busy;
> > int ret;
> >
> > @@ -862,12 +885,16 @@ static int __i915_ttm_get_pages(struct
> > drm_i915_gem_object *obj,
> > }
> >
> > if (!i915_gem_object_has_pages(obj)) {
> > - /* Object either has a page vector or is an iomem
> > object */
> > - st = bo->ttm ? i915_ttm_tt_get_st(bo->ttm) : obj-
> > >ttm.cached_io_st;
> > - if (IS_ERR(st))
> > - return PTR_ERR(st);
> > + struct i915_refct_sgt *rsgt =
> > + i915_ttm_resource_get_st(obj, bo-
> > >resource);
> > +
> > + if (IS_ERR(rsgt))
> > + return PTR_ERR(rsgt);
> >
> > - __i915_gem_object_set_pages(obj, st,
> > i915_sg_dma_sizes(st->sgl));
> > + GEM_BUG_ON(obj->mm.rsgt);
> > + obj->mm.rsgt = rsgt;
> > + __i915_gem_object_set_pages(obj, &rsgt->table,
> > + i915_sg_dma_sizes(rsgt-
> > >table.sgl));
> > }
> >
> > i915_ttm_adjust_lru(obj);
> > @@ -941,6 +968,9 @@ static void i915_ttm_put_pages(struct
> > drm_i915_gem_object *obj,
> > * If the object is not destroyed next, The TTM eviction
> > logic
> > * and shrinkers will move it out if needed.
> > */
> > +
> > + if (obj->mm.rsgt)
> > + i915_refct_sgt_put(fetch_and_zero(&obj->mm.rsgt));
> > }
> >
> > static void i915_ttm_adjust_lru(struct drm_i915_gem_object *obj)
> > @@ -1278,7 +1308,7 @@ int i915_gem_obj_copy_ttm(struct
> > drm_i915_gem_object *dst,
> > struct ttm_operation_ctx ctx = {
> > .interruptible = intr,
> > };
> > - struct sg_table *dst_st;
> > + struct i915_refct_sgt *dst_rsgt;
> > int ret;
> >
> > assert_object_held(dst);
> > @@ -1293,11 +1323,11 @@ int i915_gem_obj_copy_ttm(struct
> > drm_i915_gem_object *dst,
> > if (ret)
> > return ret;
> >
> > - dst_st = gpu_binds_iomem(dst_bo->resource) ?
> > - dst->ttm.cached_io_st : i915_ttm_tt_get_st(dst_bo-
> > >ttm);
> > -
> > + dst_rsgt = i915_ttm_resource_get_st(dst, dst_bo->resource);
> > __i915_ttm_move(src_bo, false, dst_bo->resource, dst_bo-
> > >ttm,
> > - dst_st, allow_accel);
> > + dst_rsgt, allow_accel);
> > +
> > + i915_refct_sgt_put(dst_rsgt);
> >
> > return 0;
> > }
> > diff --git a/drivers/gpu/drm/i915/i915_scatterlist.c
> > b/drivers/gpu/drm/i915/i915_scatterlist.c
> > index 4a6712dca838..41f2adb6a583 100644
> > --- a/drivers/gpu/drm/i915/i915_scatterlist.c
> > +++ b/drivers/gpu/drm/i915/i915_scatterlist.c
> > @@ -41,8 +41,32 @@ bool i915_sg_trim(struct sg_table *orig_st)
> > return true;
> > }
> >
> > +static void i915_refct_sgt_release(struct kref *ref)
> > +{
> > + struct i915_refct_sgt *rsgt =
> > + container_of(ref, typeof(*rsgt), kref);
> > +
> > + sg_free_table(&rsgt->table);
> > + kfree(rsgt);
> > +}
> > +
> > +static const struct i915_refct_sgt_ops rsgt_ops = {
> > + .release = i915_refct_sgt_release
> > +};
> > +
> > +/**
> > + * i915_refct_sgt_init - Initialize a struct i915_refct_sgt with
> > default ops
> > + * @rsgt: The struct i915_refct_sgt to initialize.
> > + * size: The size of the underlying memory buffer.
> > + */
> > +void i915_refct_sgt_init(struct i915_refct_sgt *rsgt, size_t size)
> > +{
> > + __i915_refct_sgt_init(rsgt, size, &rsgt_ops);
> > +}
> > +
> > /**
> > - * i915_sg_from_mm_node - Create an sg_table from a struct
> > drm_mm_node
> > + * i915_rsgt_from_mm_node - Create a refcounted sg_table from a
> > struct
> > + * drm_mm_node
> > * @node: The drm_mm_node.
> > * @region_start: An offset to add to the dma addresses of the sg
> > list.
> > *
> > @@ -50,25 +74,28 @@ bool i915_sg_trim(struct sg_table *orig_st)
> > * taking a maximum segment length into account, splitting into
> > segments
> > * if necessary.
> > *
> > - * Return: A pointer to a kmalloced struct sg_table on success,
> > negative
> > + * Return: A pointer to a kmalloced struct i915_refct_sgt on
> > success, negative
> > * error code cast to an error pointer on failure.
> > */
> > -struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node
> > *node,
> > - u64 region_start)
> > +struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct
> > drm_mm_node *node,
> > + u64 region_start)
> > {
> > const u64 max_segment = SZ_1G; /* Do we have a limit on
> > this? */
> > u64 segment_pages = max_segment >> PAGE_SHIFT;
> > u64 block_size, offset, prev_end;
> > + struct i915_refct_sgt *rsgt;
> > struct sg_table *st;
> > struct scatterlist *sg;
> >
> > - st = kmalloc(sizeof(*st), GFP_KERNEL);
> > - if (!st)
> > + rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
> > + if (!rsgt)
> > return ERR_PTR(-ENOMEM);
> >
> > + i915_refct_sgt_init(rsgt, node->size << PAGE_SHIFT);
> > + st = &rsgt->table;
> > if (sg_alloc_table(st, DIV_ROUND_UP(node->size,
> > segment_pages),
> > GFP_KERNEL)) {
> > - kfree(st);
> > + i915_refct_sgt_put(rsgt);
> > return ERR_PTR(-ENOMEM);
> > }
> >
> > @@ -104,11 +131,11 @@ struct sg_table *i915_sg_from_mm_node(const
> > struct drm_mm_node *node,
> > sg_mark_end(sg);
> > i915_sg_trim(st);
> >
> > - return st;
> > + return rsgt;
> > }
> >
> > /**
> > - * i915_sg_from_buddy_resource - Create an sg_table from a struct
> > + * i915_rsgt_from_buddy_resource - Create a refcounted sg_table
> > from a struct
> > * i915_buddy_block list
> > * @res: The struct i915_ttm_buddy_resource.
> > * @region_start: An offset to add to the dma addresses of the sg
> > list.
> > @@ -117,11 +144,11 @@ struct sg_table *i915_sg_from_mm_node(const
> > struct drm_mm_node *node,
> > * taking a maximum segment length into account, splitting into
> > segments
> > * if necessary.
> > *
> > - * Return: A pointer to a kmalloced struct sg_table on success,
> > negative
> > + * Return: A pointer to a kmalloced struct i915_refct_sgts on
> > success, negative
> > * error code cast to an error pointer on failure.
> > */
> > -struct sg_table *i915_sg_from_buddy_resource(struct ttm_resource
> > *res,
> > - u64 region_start)
> > +struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct
> > ttm_resource *res,
> > + u64
> > region_start)
> > {
> > struct i915_ttm_buddy_resource *bman_res =
> > to_ttm_buddy_resource(res);
> > const u64 size = res->num_pages << PAGE_SHIFT;
> > @@ -129,18 +156,21 @@ struct sg_table
> > *i915_sg_from_buddy_resource(struct ttm_resource *res,
> > struct i915_buddy_mm *mm = bman_res->mm;
> > struct list_head *blocks = &bman_res->blocks;
> > struct i915_buddy_block *block;
> > + struct i915_refct_sgt *rsgt;
> > struct scatterlist *sg;
> > struct sg_table *st;
> > resource_size_t prev_end;
> >
> > GEM_BUG_ON(list_empty(blocks));
> >
> > - st = kmalloc(sizeof(*st), GFP_KERNEL);
> > - if (!st)
> > + rsgt = kmalloc(sizeof(*rsgt), GFP_KERNEL);
> > + if (!rsgt)
> > return ERR_PTR(-ENOMEM);
> >
> > + i915_refct_sgt_init(rsgt, size);
> > + st = &rsgt->table;
> > if (sg_alloc_table(st, res->num_pages, GFP_KERNEL)) {
> > - kfree(st);
> > + i915_refct_sgt_put(rsgt);
> > return ERR_PTR(-ENOMEM);
> > }
> >
> > @@ -181,7 +211,7 @@ struct sg_table
> > *i915_sg_from_buddy_resource(struct ttm_resource *res,
> > sg_mark_end(sg);
> > i915_sg_trim(st);
> >
> > - return st;
> > + return rsgt;
> > }
> >
> > #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
> > diff --git a/drivers/gpu/drm/i915/i915_scatterlist.h
> > b/drivers/gpu/drm/i915/i915_scatterlist.h
> > index b8bd5925b03f..12c6a1684081 100644
> > --- a/drivers/gpu/drm/i915/i915_scatterlist.h
> > +++ b/drivers/gpu/drm/i915/i915_scatterlist.h
> > @@ -144,10 +144,78 @@ static inline unsigned int
> > i915_sg_segment_size(void)
> >
> > bool i915_sg_trim(struct sg_table *orig_st);
> >
> > -struct sg_table *i915_sg_from_mm_node(const struct drm_mm_node
> > *node,
> > - u64 region_start);
> > +/**
> > + * struct i915_refct_sgt_ops - Operations structure for struct
> > i915_refct_sgt
> > + */
> > +struct i915_refct_sgt_ops {
> > + /**
> > + * release() - Free the memory of the struct i915_refct_sgt
> > + * @ref: struct kref that is embedded in the struct
> > i915_refct_sgt
> > + */
> > + void (*release)(struct kref *ref);
> > +};
> > +
> > +/**
> > + * struct i915_refct_sgt - A refcounted scatter-gather table
> > + * @kref: struct kref for refcounting
> > + * @table: struct sg_table holding the scatter-gather table
> > itself. Note that
> > + * @table->sgl = NULL can be used to determine whether a scatter-
> > gather table
> > + * is present or not.
> > + * @size: The size in bytes of the underlying memory buffer
> > + * @ops: The operations structure.
> > + */
> > +struct i915_refct_sgt {
> > + struct kref kref;
> > + struct sg_table table;
> > + size_t size;
> > + const struct i915_refct_sgt_ops *ops;
> > +};
> > +
> > +/**
> > + * i915_refct_sgt_put - Put a refcounted sg-table
> > + * @rsgt the struct i915_refct_sgt to put.
> > + */
> > +static inline void i915_refct_sgt_put(struct i915_refct_sgt *rsgt)
> > +{
> > + if (rsgt)
> > + kref_put(&rsgt->kref, rsgt->ops->release);
> > +}
> > +
> > +/**
> > + * i915_refct_sgt_get - Get a refcounted sg-table
> > + * @rsgt the struct i915_refct_sgt to get.
> > + */
> > +static inline struct i915_refct_sgt *
> > +i915_refct_sgt_get(struct i915_refct_sgt *rsgt)
> > +{
> > + kref_get(&rsgt->kref);
> > + return rsgt;
> > +}
> > +
> > +/**
> > + * __i915_refct_sgt_init - Initialize a refcounted sg-list with a
> > custom
> > + * operations structure
> > + * @rsgt The struct i915_refct_sgt to initialize.
> > + * @size: Size in bytes of the underlying memory buffer.
> > + * @ops: A customized operations structure in case the refcounted
> > sg-list
> > + * is embedded into another structure.
> > + */
> > +static inline void __i915_refct_sgt_init(struct i915_refct_sgt
> > *rsgt,
> > + size_t size,
> > + const struct
> > i915_refct_sgt_ops *ops)
> > +{
> > + kref_init(&rsgt->kref);
> > + rsgt->table.sgl = NULL;
> > + rsgt->size = size;
> > + rsgt->ops = ops;
> > +}
> > +
> > +void i915_refct_sgt_init(struct i915_refct_sgt *rsgt, size_t
> > size);
> > +
> > +struct i915_refct_sgt *i915_rsgt_from_mm_node(const struct
> > drm_mm_node *node,
> > + u64 region_start);
> >
> > -struct sg_table *i915_sg_from_buddy_resource(struct ttm_resource
> > *res,
> > - u64 region_start);
> > +struct i915_refct_sgt *i915_rsgt_from_buddy_resource(struct
> > ttm_resource *res,
> > + u64
> > region_start);
> >
> > #endif
> > diff --git a/drivers/gpu/drm/i915/intel_region_ttm.c
> > b/drivers/gpu/drm/i915/intel_region_ttm.c
> > index 98c7339bf8ba..2e901a27e259 100644
> > --- a/drivers/gpu/drm/i915/intel_region_ttm.c
> > +++ b/drivers/gpu/drm/i915/intel_region_ttm.c
> > @@ -115,8 +115,8 @@ void intel_region_ttm_fini(struct
> > intel_memory_region *mem)
> > }
> >
> > /**
> > - * intel_region_ttm_resource_to_st - Convert an opaque TTM
> > resource manager resource
> > - * to an sg_table.
> > + * intel_region_ttm_resource_to_rsgt -
> > + * Convert an opaque TTM resource manager resource to a refcounted
> > sg_table.
> > * @mem: The memory region.
> > * @res: The resource manager resource obtained from the TTM
> > resource manager.
> > *
> > @@ -126,17 +126,18 @@ void intel_region_ttm_fini(struct
> > intel_memory_region *mem)
> > *
> > * Return: A malloced sg_table on success, an error pointer on
> > failure.
> > */
> > -struct sg_table *intel_region_ttm_resource_to_st(struct
> > intel_memory_region *mem,
> > - struct
> > ttm_resource *res)
> > +struct i915_refct_sgt *
> > +intel_region_ttm_resource_to_rsgt(struct intel_memory_region *mem,
> > + struct ttm_resource *res)
> > {
> > if (mem->is_range_manager) {
> > struct ttm_range_mgr_node *range_node =
> > to_ttm_range_mgr_node(res);
> >
> > - return i915_sg_from_mm_node(&range_node-
> > >mm_nodes[0],
> > - mem->region.start);
> > + return i915_rsgt_from_mm_node(&range_node-
> > >mm_nodes[0],
> > + mem->region.start);
> > } else {
> > - return i915_sg_from_buddy_resource(res, mem-
> > >region.start);
> > + return i915_rsgt_from_buddy_resource(res, mem-
> > >region.start);
> > }
> > }
> >
> > diff --git a/drivers/gpu/drm/i915/intel_region_ttm.h
> > b/drivers/gpu/drm/i915/intel_region_ttm.h
> > index 6f44075920f2..7bbe2b46b504 100644
> > --- a/drivers/gpu/drm/i915/intel_region_ttm.h
> > +++ b/drivers/gpu/drm/i915/intel_region_ttm.h
> > @@ -22,8 +22,9 @@ int intel_region_ttm_init(struct
> > intel_memory_region *mem);
> >
> > void intel_region_ttm_fini(struct intel_memory_region *mem);
> >
> > -struct sg_table *intel_region_ttm_resource_to_st(struct
> > intel_memory_region *mem,
> > - struct
> > ttm_resource *res);
> > +struct i915_refct_sgt *
> > +intel_region_ttm_resource_to_rsgt(struct intel_memory_region *mem,
> > + struct ttm_resource *res);
> >
> > void intel_region_ttm_resource_free(struct intel_memory_region
> > *mem,
> > struct ttm_resource *res);
> > diff --git a/drivers/gpu/drm/i915/selftests/mock_region.c
> > b/drivers/gpu/drm/i915/selftests/mock_region.c
> > index 75793008c4ef..7ec5037eaa58 100644
> > --- a/drivers/gpu/drm/i915/selftests/mock_region.c
> > +++ b/drivers/gpu/drm/i915/selftests/mock_region.c
> > @@ -15,9 +15,9 @@
> > static void mock_region_put_pages(struct drm_i915_gem_object
> > *obj,
> > struct sg_table *pages)
> > {
> > + i915_refct_sgt_put(obj->mm.rsgt);
> > + obj->mm.rsgt = NULL;
> > intel_region_ttm_resource_free(obj->mm.region, obj-
> > >mm.res);
> > - sg_free_table(pages);
> > - kfree(pages);
> > }
> >
> > static int mock_region_get_pages(struct drm_i915_gem_object *obj)
> > @@ -36,12 +36,14 @@ static int mock_region_get_pages(struct
> > drm_i915_gem_object *obj)
> > if (IS_ERR(obj->mm.res))
> > return PTR_ERR(obj->mm.res);
> >
> > - pages = intel_region_ttm_resource_to_st(obj->mm.region,
> > obj->mm.res);
> > - if (IS_ERR(pages)) {
> > - err = PTR_ERR(pages);
> > + obj->mm.rsgt = intel_region_ttm_resource_to_rsgt(obj-
> > >mm.region,
> > + obj-
> > >mm.res);
> > + if (IS_ERR(obj->mm.rsgt)) {
> > + err = PTR_ERR(obj->mm.rsgt);
> > goto err_free_resource;
> > }
> >
> > + pages = &obj->mm.rsgt->table;
> > __i915_gem_object_set_pages(obj, pages,
> > i915_sg_dma_sizes(pages->sgl));
> >
> > return 0;
> >
