Re: [Intel-gfx] [PATCH 13/28] drm/i915: Remove pages_mutex and intel_gtt->vma_ops.set/clear_pages members

Matthew Auld
2021-10-21T17:30:50Z

On Thu, 21 Oct 2021 at 11:36, Maarten Lankhorst
<maarten.lankhorst@linux.intel.com> wrote:
>
> Big delta, but boils down to moving set_pages to i915_vma.c, and removing
> the special handling, all callers use the defaults anyway. We only remap
> in ggtt, so default case will fall through.
>
> Because we still don't require locking in i915_vma_unpin(), handle this by
> using xchg in get_pages(), as it's locked with obj->mutex, and cmpxchg in
> unpin, which only fails if we race a against a new pin.
>
> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_dpt.c | 2 -
> drivers/gpu/drm/i915/gt/gen6_ppgtt.c | 15 -
> drivers/gpu/drm/i915/gt/intel_ggtt.c | 345 ----------------
> drivers/gpu/drm/i915/gt/intel_gtt.c | 13 -
> drivers/gpu/drm/i915/gt/intel_gtt.h | 7 -
> drivers/gpu/drm/i915/gt/intel_ppgtt.c | 12 -
> drivers/gpu/drm/i915/i915_vma.c | 388 ++++++++++++++++--
> drivers/gpu/drm/i915/i915_vma.h | 3 +
> drivers/gpu/drm/i915/i915_vma_types.h | 1 -
> drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 12 +-
> drivers/gpu/drm/i915/selftests/mock_gtt.c | 4 -
> 11 files changed, 368 insertions(+), 434 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dpt.c b/drivers/gpu/drm/i915/display/intel_dpt.c
> index 8f7b1f7534a4..ef428f3fc538 100644
> --- a/drivers/gpu/drm/i915/display/intel_dpt.c
> +++ b/drivers/gpu/drm/i915/display/intel_dpt.c
> @@ -221,8 +221,6 @@ intel_dpt_create(struct intel_framebuffer *fb)
>
> vm->vma_ops.bind_vma = dpt_bind_vma;
> vm->vma_ops.unbind_vma = dpt_unbind_vma;
> - vm->vma_ops.set_pages = ggtt_set_pages;
> - vm->vma_ops.clear_pages = clear_pages;
>
> vm->pte_encode = gen8_ggtt_pte_encode;
>
> diff --git a/drivers/gpu/drm/i915/gt/gen6_ppgtt.c b/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> index 5caa1703716e..5c048b4ccd4d 100644
> --- a/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> +++ b/drivers/gpu/drm/i915/gt/gen6_ppgtt.c
> @@ -270,19 +270,6 @@ static void gen6_ppgtt_cleanup(struct i915_address_space *vm)
> free_pd(&ppgtt->base.vm, ppgtt->base.pd);
> }
>
> -static int pd_vma_set_pages(struct i915_vma *vma)
> -{
> - vma->pages = ERR_PTR(-ENODEV);
> - return 0;
> -}
> -
> -static void pd_vma_clear_pages(struct i915_vma *vma)
> -{
> - GEM_BUG_ON(!vma->pages);
> -
> - vma->pages = NULL;
> -}
> -
> static void pd_vma_bind(struct i915_address_space *vm,
> struct i915_vm_pt_stash *stash,
> struct i915_vma *vma,
> @@ -322,8 +309,6 @@ static void pd_vma_unbind(struct i915_address_space *vm, struct i915_vma *vma)
> }
>
> static const struct i915_vma_ops pd_vma_ops = {
> - .set_pages = pd_vma_set_pages,
> - .clear_pages = pd_vma_clear_pages,
> .bind_vma = pd_vma_bind,
> .unbind_vma = pd_vma_unbind,
> };
> diff --git a/drivers/gpu/drm/i915/gt/intel_ggtt.c b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> index f17383e76eb7..6da57199bb33 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ggtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ggtt.c
> @@ -20,9 +20,6 @@
> #include "intel_gtt.h"
> #include "gen8_ppgtt.h"
>
> -static int
> -i915_get_ggtt_vma_pages(struct i915_vma *vma);
> -
> static void i915_ggtt_color_adjust(const struct drm_mm_node *node,
> unsigned long color,
> u64 *start,
> @@ -875,21 +872,6 @@ static int ggtt_probe_common(struct i915_ggtt *ggtt, u64 size)
> return 0;
> }
>
> -int ggtt_set_pages(struct i915_vma *vma)
> -{
> - int ret;
> -
> - GEM_BUG_ON(vma->pages);
> -
> - ret = i915_get_ggtt_vma_pages(vma);
> - if (ret)
> - return ret;
> -
> - vma->page_sizes = vma->obj->mm.page_sizes;
> -
> - return 0;
> -}
> -
> static void gen6_gmch_remove(struct i915_address_space *vm)
> {
> struct i915_ggtt *ggtt = i915_vm_to_ggtt(vm);
> @@ -950,8 +932,6 @@ static int gen8_gmch_probe(struct i915_ggtt *ggtt)
>
> ggtt->vm.vma_ops.bind_vma = ggtt_bind_vma;
> ggtt->vm.vma_ops.unbind_vma = ggtt_unbind_vma;
> - ggtt->vm.vma_ops.set_pages = ggtt_set_pages;
> - ggtt->vm.vma_ops.clear_pages = clear_pages;
>
> ggtt->vm.pte_encode = gen8_ggtt_pte_encode;
>
> @@ -1100,8 +1080,6 @@ static int gen6_gmch_probe(struct i915_ggtt *ggtt)
>
> ggtt->vm.vma_ops.bind_vma = ggtt_bind_vma;
> ggtt->vm.vma_ops.unbind_vma = ggtt_unbind_vma;
> - ggtt->vm.vma_ops.set_pages = ggtt_set_pages;
> - ggtt->vm.vma_ops.clear_pages = clear_pages;
>
> return ggtt_probe_common(ggtt, size);
> }
> @@ -1145,8 +1123,6 @@ static int i915_gmch_probe(struct i915_ggtt *ggtt)
>
> ggtt->vm.vma_ops.bind_vma = ggtt_bind_vma;
> ggtt->vm.vma_ops.unbind_vma = ggtt_unbind_vma;
> - ggtt->vm.vma_ops.set_pages = ggtt_set_pages;
> - ggtt->vm.vma_ops.clear_pages = clear_pages;
>
> if (unlikely(ggtt->do_idle_maps))
> drm_notice(&i915->drm,
> @@ -1294,324 +1270,3 @@ void i915_ggtt_resume(struct i915_ggtt *ggtt)
>
> intel_ggtt_restore_fences(ggtt);
> }
> -
> -static struct scatterlist *
> -rotate_pages(struct drm_i915_gem_object *obj, unsigned int offset,
> - unsigned int width, unsigned int height,
> - unsigned int src_stride, unsigned int dst_stride,
> - struct sg_table *st, struct scatterlist *sg)
> -{
> - unsigned int column, row;
> - unsigned int src_idx;
> -
> - for (column = 0; column < width; column++) {
> - unsigned int left;
> -
> - src_idx = src_stride * (height - 1) + column + offset;
> - for (row = 0; row < height; row++) {
> - st->nents++;
> - /*
> - * We don't need the pages, but need to initialize
> - * the entries so the sg list can be happily traversed.
> - * The only thing we need are DMA addresses.
> - */
> - sg_set_page(sg, NULL, I915_GTT_PAGE_SIZE, 0);
> - sg_dma_address(sg) =
> - i915_gem_object_get_dma_address(obj, src_idx);
> - sg_dma_len(sg) = I915_GTT_PAGE_SIZE;
> - sg = sg_next(sg);
> - src_idx -= src_stride;
> - }
> -
> - left = (dst_stride - height) * I915_GTT_PAGE_SIZE;
> -
> - if (!left)
> - continue;
> -
> - st->nents++;
> -
> - /*
> - * The DE ignores the PTEs for the padding tiles, the sg entry
> - * here is just a conenience to indicate how many padding PTEs
> - * to insert at this spot.
> - */
> - sg_set_page(sg, NULL, left, 0);
> - sg_dma_address(sg) = 0;
> - sg_dma_len(sg) = left;
> - sg = sg_next(sg);
> - }
> -
> - return sg;
> -}
> -
> -static noinline struct sg_table *
> -intel_rotate_pages(struct intel_rotation_info *rot_info,
> - struct drm_i915_gem_object *obj)
> -{
> - unsigned int size = intel_rotation_info_size(rot_info);
> - struct drm_i915_private *i915 = to_i915(obj->base.dev);
> - struct sg_table *st;
> - struct scatterlist *sg;
> - int ret = -ENOMEM;
> - int i;
> -
> - /* Allocate target SG list. */
> - st = kmalloc(sizeof(*st), GFP_KERNEL);
> - if (!st)
> - goto err_st_alloc;
> -
> - ret = sg_alloc_table(st, size, GFP_KERNEL);
> - if (ret)
> - goto err_sg_alloc;
> -
> - st->nents = 0;
> - sg = st->sgl;
> -
> - for (i = 0 ; i < ARRAY_SIZE(rot_info->plane); i++)
> - sg = rotate_pages(obj, rot_info->plane[i].offset,
> - rot_info->plane[i].width, rot_info->plane[i].height,
> - rot_info->plane[i].src_stride,
> - rot_info->plane[i].dst_stride,
> - st, sg);
> -
> - return st;
> -
> -err_sg_alloc:
> - kfree(st);
> -err_st_alloc:
> -
> - drm_dbg(&i915->drm, "Failed to create rotated mapping for object size %zu! (%ux%u tiles, %u pages)\n",
> - obj->base.size, rot_info->plane[0].width,
> - rot_info->plane[0].height, size);
> -
> - return ERR_PTR(ret);
> -}
> -
> -static struct scatterlist *
> -remap_pages(struct drm_i915_gem_object *obj,
> - unsigned int offset, unsigned int alignment_pad,
> - unsigned int width, unsigned int height,
> - unsigned int src_stride, unsigned int dst_stride,
> - struct sg_table *st, struct scatterlist *sg)
> -{
> - unsigned int row;
> -
> - if (alignment_pad) {
> - st->nents++;
> -
> - /*
> - * The DE ignores the PTEs for the padding tiles, the sg entry
> - * here is just a convenience to indicate how many padding PTEs
> - * to insert at this spot.
> - */
> - sg_set_page(sg, NULL, alignment_pad * 4096, 0);
> - sg_dma_address(sg) = 0;
> - sg_dma_len(sg) = alignment_pad * 4096;
> - sg = sg_next(sg);
> - }
> -
> - for (row = 0; row < height; row++) {
> - unsigned int left = width * I915_GTT_PAGE_SIZE;
> -
> - while (left) {
> - dma_addr_t addr;
> - unsigned int length;
> -
> - /*
> - * We don't need the pages, but need to initialize
> - * the entries so the sg list can be happily traversed.
> - * The only thing we need are DMA addresses.
> - */
> -
> - addr = i915_gem_object_get_dma_address_len(obj, offset, &length);
> -
> - length = min(left, length);
> -
> - st->nents++;
> -
> - sg_set_page(sg, NULL, length, 0);
> - sg_dma_address(sg) = addr;
> - sg_dma_len(sg) = length;
> - sg = sg_next(sg);
> -
> - offset += length / I915_GTT_PAGE_SIZE;
> - left -= length;
> - }
> -
> - offset += src_stride - width;
> -
> - left = (dst_stride - width) * I915_GTT_PAGE_SIZE;
> -
> - if (!left)
> - continue;
> -
> - st->nents++;
> -
> - /*
> - * The DE ignores the PTEs for the padding tiles, the sg entry
> - * here is just a conenience to indicate how many padding PTEs
> - * to insert at this spot.
> - */
> - sg_set_page(sg, NULL, left, 0);
> - sg_dma_address(sg) = 0;
> - sg_dma_len(sg) = left;
> - sg = sg_next(sg);
> - }
> -
> - return sg;
> -}
> -
> -static noinline struct sg_table *
> -intel_remap_pages(struct intel_remapped_info *rem_info,
> - struct drm_i915_gem_object *obj)
> -{
> - unsigned int size = intel_remapped_info_size(rem_info);
> - struct drm_i915_private *i915 = to_i915(obj->base.dev);
> - struct sg_table *st;
> - struct scatterlist *sg;
> - unsigned int gtt_offset = 0;
> - int ret = -ENOMEM;
> - int i;
> -
> - /* Allocate target SG list. */
> - st = kmalloc(sizeof(*st), GFP_KERNEL);
> - if (!st)
> - goto err_st_alloc;
> -
> - ret = sg_alloc_table(st, size, GFP_KERNEL);
> - if (ret)
> - goto err_sg_alloc;
> -
> - st->nents = 0;
> - sg = st->sgl;
> -
> - for (i = 0 ; i < ARRAY_SIZE(rem_info->plane); i++) {
> - unsigned int alignment_pad = 0;
> -
> - if (rem_info->plane_alignment)
> - alignment_pad = ALIGN(gtt_offset, rem_info->plane_alignment) - gtt_offset;
> -
> - sg = remap_pages(obj,
> - rem_info->plane[i].offset, alignment_pad,
> - rem_info->plane[i].width, rem_info->plane[i].height,
> - rem_info->plane[i].src_stride, rem_info->plane[i].dst_stride,
> - st, sg);
> -
> - gtt_offset += alignment_pad +
> - rem_info->plane[i].dst_stride * rem_info->plane[i].height;
> - }
> -
> - i915_sg_trim(st);
> -
> - return st;
> -
> -err_sg_alloc:
> - kfree(st);
> -err_st_alloc:
> -
> - drm_dbg(&i915->drm, "Failed to create remapped mapping for object size %zu! (%ux%u tiles, %u pages)\n",
> - obj->base.size, rem_info->plane[0].width,
> - rem_info->plane[0].height, size);
> -
> - return ERR_PTR(ret);
> -}
> -
> -static noinline struct sg_table *
> -intel_partial_pages(const struct i915_ggtt_view *view,
> - struct drm_i915_gem_object *obj)
> -{
> - struct sg_table *st;
> - struct scatterlist *sg, *iter;
> - unsigned int count = view->partial.size;
> - unsigned int offset;
> - int ret = -ENOMEM;
> -
> - st = kmalloc(sizeof(*st), GFP_KERNEL);
> - if (!st)
> - goto err_st_alloc;
> -
> - ret = sg_alloc_table(st, count, GFP_KERNEL);
> - if (ret)
> - goto err_sg_alloc;
> -
> - iter = i915_gem_object_get_sg_dma(obj, view->partial.offset, &offset);
> - GEM_BUG_ON(!iter);
> -
> - sg = st->sgl;
> - st->nents = 0;
> - do {
> - unsigned int len;
> -
> - len = min(sg_dma_len(iter) - (offset << PAGE_SHIFT),
> - count << PAGE_SHIFT);
> - sg_set_page(sg, NULL, len, 0);
> - sg_dma_address(sg) =
> - sg_dma_address(iter) + (offset << PAGE_SHIFT);
> - sg_dma_len(sg) = len;
> -
> - st->nents++;
> - count -= len >> PAGE_SHIFT;
> - if (count == 0) {
> - sg_mark_end(sg);
> - i915_sg_trim(st); /* Drop any unused tail entries. */
> -
> - return st;
> - }
> -
> - sg = __sg_next(sg);
> - iter = __sg_next(iter);
> - offset = 0;
> - } while (1);
> -
> -err_sg_alloc:
> - kfree(st);
> -err_st_alloc:
> - return ERR_PTR(ret);
> -}
> -
> -static int
> -i915_get_ggtt_vma_pages(struct i915_vma *vma)
> -{
> - int ret;
> -
> - /*
> - * The vma->pages are only valid within the lifespan of the borrowed
> - * obj->mm.pages. When the obj->mm.pages sg_table is regenerated, so
> - * must be the vma->pages. A simple rule is that vma->pages must only
> - * be accessed when the obj->mm.pages are pinned.
> - */
> - GEM_BUG_ON(!i915_gem_object_has_pinned_pages(vma->obj));
> -
> - switch (vma->ggtt_view.type) {
> - default:
> - GEM_BUG_ON(vma->ggtt_view.type);
> - fallthrough;
> - case I915_GGTT_VIEW_NORMAL:
> - vma->pages = vma->obj->mm.pages;
> - return 0;
> -
> - case I915_GGTT_VIEW_ROTATED:
> - vma->pages =
> - intel_rotate_pages(&vma->ggtt_view.rotated, vma->obj);
> - break;
> -
> - case I915_GGTT_VIEW_REMAPPED:
> - vma->pages =
> - intel_remap_pages(&vma->ggtt_view.remapped, vma->obj);
> - break;
> -
> - case I915_GGTT_VIEW_PARTIAL:
> - vma->pages = intel_partial_pages(&vma->ggtt_view, vma->obj);
> - break;
> - }
> -
> - ret = 0;
> - if (IS_ERR(vma->pages)) {
> - ret = PTR_ERR(vma->pages);
> - vma->pages = NULL;
> - drm_err(&vma->vm->i915->drm,
> - "Failed to get pages for VMA view type %u (%d)!\n",
> - vma->ggtt_view.type, ret);
> - }
> - return ret;
> -}
> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.c b/drivers/gpu/drm/i915/gt/intel_gtt.c
> index 67d14afa6623..12eed5fcb17a 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.c
> @@ -221,19 +221,6 @@ void i915_address_space_init(struct i915_address_space *vm, int subclass)
> INIT_LIST_HEAD(&vm->bound_list);
> }
>
> -void clear_pages(struct i915_vma *vma)
> -{
> - GEM_BUG_ON(!vma->pages);
> -
> - if (vma->pages != vma->obj->mm.pages) {
> - sg_free_table(vma->pages);
> - kfree(vma->pages);
> - }
> - vma->pages = NULL;
> -
> - memset(&vma->page_sizes, 0, sizeof(vma->page_sizes));
> -}
> -
> void *__px_vaddr(struct drm_i915_gem_object *p)
> {
> enum i915_map_type type;
> diff --git a/drivers/gpu/drm/i915/gt/intel_gtt.h b/drivers/gpu/drm/i915/gt/intel_gtt.h
> index bc6750263359..306e7645fdc5 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gtt.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gtt.h
> @@ -206,9 +206,6 @@ struct i915_vma_ops {
> */
> void (*unbind_vma)(struct i915_address_space *vm,
> struct i915_vma *vma);
> -
> - int (*set_pages)(struct i915_vma *vma);
> - void (*clear_pages)(struct i915_vma *vma);
> };
>
> struct i915_address_space {
> @@ -594,10 +591,6 @@ release_pd_entry(struct i915_page_directory * const pd,
> const struct drm_i915_gem_object * const scratch);
> void gen6_ggtt_invalidate(struct i915_ggtt *ggtt);
>
> -int ggtt_set_pages(struct i915_vma *vma);
> -int ppgtt_set_pages(struct i915_vma *vma);
> -void clear_pages(struct i915_vma *vma);
> -
> void ppgtt_bind_vma(struct i915_address_space *vm,
> struct i915_vm_pt_stash *stash,
> struct i915_vma *vma,
> diff --git a/drivers/gpu/drm/i915/gt/intel_ppgtt.c b/drivers/gpu/drm/i915/gt/intel_ppgtt.c
> index 4396bfd630d8..083b3090c69c 100644
> --- a/drivers/gpu/drm/i915/gt/intel_ppgtt.c
> +++ b/drivers/gpu/drm/i915/gt/intel_ppgtt.c
> @@ -289,16 +289,6 @@ void i915_vm_free_pt_stash(struct i915_address_space *vm,
> }
> }
>
> -int ppgtt_set_pages(struct i915_vma *vma)
> -{
> - GEM_BUG_ON(vma->pages);
> -
> - vma->pages = vma->obj->mm.pages;
> - vma->page_sizes = vma->obj->mm.page_sizes;
> -
> - return 0;
> -}
> -
> void ppgtt_init(struct i915_ppgtt *ppgtt, struct intel_gt *gt,
> unsigned long lmem_pt_obj_flags)
> {
> @@ -315,6 +305,4 @@ void ppgtt_init(struct i915_ppgtt *ppgtt, struct intel_gt *gt,
>
> ppgtt->vm.vma_ops.bind_vma = ppgtt_bind_vma;
> ppgtt->vm.vma_ops.unbind_vma = ppgtt_unbind_vma;
> - ppgtt->vm.vma_ops.set_pages = ppgtt_set_pages;
> - ppgtt->vm.vma_ops.clear_pages = clear_pages;
> }
> diff --git a/drivers/gpu/drm/i915/i915_vma.c b/drivers/gpu/drm/i915/i915_vma.c
> index ac09b685678a..bacc8d68e495 100644
> --- a/drivers/gpu/drm/i915/i915_vma.c
> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -112,7 +112,6 @@ vma_create(struct drm_i915_gem_object *obj,
> return ERR_PTR(-ENOMEM);
>
> kref_init(&vma->ref);
> - mutex_init(&vma->pages_mutex);
> vma->vm = i915_vm_get(vm);
> vma->ops = &vm->vma_ops;
> vma->obj = obj;
> @@ -789,10 +788,343 @@ static bool try_qad_pin(struct i915_vma *vma, unsigned int flags)
> return pinned;
> }
>
> -static int vma_get_pages(struct i915_vma *vma)
> +
> +
> +static struct scatterlist *
> +rotate_pages(struct drm_i915_gem_object *obj, unsigned int offset,
> + unsigned int width, unsigned int height,
> + unsigned int src_stride, unsigned int dst_stride,
> + struct sg_table *st, struct scatterlist *sg)
> {
> - int err = 0;
> - bool pinned_pages = true;
> + unsigned int column, row;
> + unsigned int src_idx;
> +
> + for (column = 0; column < width; column++) {
> + unsigned int left;
> +
> + src_idx = src_stride * (height - 1) + column + offset;
> + for (row = 0; row < height; row++) {
> + st->nents++;
> + /*
> + * We don't need the pages, but need to initialize
> + * the entries so the sg list can be happily traversed.
> + * The only thing we need are DMA addresses.
> + */
> + sg_set_page(sg, NULL, I915_GTT_PAGE_SIZE, 0);
> + sg_dma_address(sg) =
> + i915_gem_object_get_dma_address(obj, src_idx);
> + sg_dma_len(sg) = I915_GTT_PAGE_SIZE;
> + sg = sg_next(sg);
> + src_idx -= src_stride;
> + }
> +
> + left = (dst_stride - height) * I915_GTT_PAGE_SIZE;
> +
> + if (!left)
> + continue;
> +
> + st->nents++;
> +
> + /*
> + * The DE ignores the PTEs for the padding tiles, the sg entry
> + * here is just a conenience to indicate how many padding PTEs
> + * to insert at this spot.
> + */
> + sg_set_page(sg, NULL, left, 0);
> + sg_dma_address(sg) = 0;
> + sg_dma_len(sg) = left;
> + sg = sg_next(sg);
> + }
> +
> + return sg;
> +}
> +
> +static noinline struct sg_table *
> +intel_rotate_pages(struct intel_rotation_info *rot_info,
> + struct drm_i915_gem_object *obj)
> +{
> + unsigned int size = intel_rotation_info_size(rot_info);
> + struct drm_i915_private *i915 = to_i915(obj->base.dev);
> + struct sg_table *st;
> + struct scatterlist *sg;
> + int ret = -ENOMEM;
> + int i;
> +
> + /* Allocate target SG list. */
> + st = kmalloc(sizeof(*st), GFP_KERNEL);
> + if (!st)
> + goto err_st_alloc;
> +
> + ret = sg_alloc_table(st, size, GFP_KERNEL);
> + if (ret)
> + goto err_sg_alloc;
> +
> + st->nents = 0;
> + sg = st->sgl;
> +
> + for (i = 0 ; i < ARRAY_SIZE(rot_info->plane); i++)
> + sg = rotate_pages(obj, rot_info->plane[i].offset,
> + rot_info->plane[i].width, rot_info->plane[i].height,
> + rot_info->plane[i].src_stride,
> + rot_info->plane[i].dst_stride,
> + st, sg);
> +
> + return st;
> +
> +err_sg_alloc:
> + kfree(st);
> +err_st_alloc:
> +
> + drm_dbg(&i915->drm, "Failed to create rotated mapping for object size %zu! (%ux%u tiles, %u pages)\n",
> + obj->base.size, rot_info->plane[0].width,
> + rot_info->plane[0].height, size);
> +
> + return ERR_PTR(ret);
> +}
> +
> +static struct scatterlist *
> +remap_pages(struct drm_i915_gem_object *obj,
> + unsigned int offset, unsigned int alignment_pad,
> + unsigned int width, unsigned int height,
> + unsigned int src_stride, unsigned int dst_stride,
> + struct sg_table *st, struct scatterlist *sg)
> +{
> + unsigned int row;
> +
> + if (alignment_pad) {
> + st->nents++;
> +
> + /*
> + * The DE ignores the PTEs for the padding tiles, the sg entry
> + * here is just a convenience to indicate how many padding PTEs
> + * to insert at this spot.
> + */
> + sg_set_page(sg, NULL, alignment_pad * 4096, 0);
> + sg_dma_address(sg) = 0;
> + sg_dma_len(sg) = alignment_pad * 4096;
> + sg = sg_next(sg);
> + }
> +
> + for (row = 0; row < height; row++) {
> + unsigned int left = width * I915_GTT_PAGE_SIZE;
> +
> + while (left) {
> + dma_addr_t addr;
> + unsigned int length;
> +
> + /*
> + * We don't need the pages, but need to initialize
> + * the entries so the sg list can be happily traversed.
> + * The only thing we need are DMA addresses.
> + */
> +
> + addr = i915_gem_object_get_dma_address_len(obj, offset, &length);
> +
> + length = min(left, length);
> +
> + st->nents++;
> +
> + sg_set_page(sg, NULL, length, 0);
> + sg_dma_address(sg) = addr;
> + sg_dma_len(sg) = length;
> + sg = sg_next(sg);
> +
> + offset += length / I915_GTT_PAGE_SIZE;
> + left -= length;
> + }
> +
> + offset += src_stride - width;
> +
> + left = (dst_stride - width) * I915_GTT_PAGE_SIZE;
> +
> + if (!left)
> + continue;
> +
> + st->nents++;
> +
> + /*
> + * The DE ignores the PTEs for the padding tiles, the sg entry
> + * here is just a conenience to indicate how many padding PTEs
> + * to insert at this spot.
> + */
> + sg_set_page(sg, NULL, left, 0);
> + sg_dma_address(sg) = 0;
> + sg_dma_len(sg) = left;
> + sg = sg_next(sg);
> + }
> +
> + return sg;
> +}
> +
> +static noinline struct sg_table *
> +intel_remap_pages(struct intel_remapped_info *rem_info,
> + struct drm_i915_gem_object *obj)
> +{
> + unsigned int size = intel_remapped_info_size(rem_info);
> + struct drm_i915_private *i915 = to_i915(obj->base.dev);
> + struct sg_table *st;
> + struct scatterlist *sg;
> + unsigned int gtt_offset = 0;
> + int ret = -ENOMEM;
> + int i;
> +
> + /* Allocate target SG list. */
> + st = kmalloc(sizeof(*st), GFP_KERNEL);
> + if (!st)
> + goto err_st_alloc;
> +
> + ret = sg_alloc_table(st, size, GFP_KERNEL);
> + if (ret)
> + goto err_sg_alloc;
> +
> + st->nents = 0;
> + sg = st->sgl;
> +
> + for (i = 0 ; i < ARRAY_SIZE(rem_info->plane); i++) {
> + unsigned int alignment_pad = 0;
> +
> + if (rem_info->plane_alignment)
> + alignment_pad = ALIGN(gtt_offset, rem_info->plane_alignment) - gtt_offset;
> +
> + sg = remap_pages(obj,
> + rem_info->plane[i].offset, alignment_pad,
> + rem_info->plane[i].width, rem_info->plane[i].height,
> + rem_info->plane[i].src_stride, rem_info->plane[i].dst_stride,
> + st, sg);
> +
> + gtt_offset += alignment_pad +
> + rem_info->plane[i].dst_stride * rem_info->plane[i].height;
> + }
> +
> + i915_sg_trim(st);
> +
> + return st;
> +
> +err_sg_alloc:
> + kfree(st);
> +err_st_alloc:
> +
> + drm_dbg(&i915->drm, "Failed to create remapped mapping for object size %zu! (%ux%u tiles, %u pages)\n",
> + obj->base.size, rem_info->plane[0].width,
> + rem_info->plane[0].height, size);
> +
> + return ERR_PTR(ret);
> +}
> +
> +static noinline struct sg_table *
> +intel_partial_pages(const struct i915_ggtt_view *view,
> + struct drm_i915_gem_object *obj)
> +{
> + struct sg_table *st;
> + struct scatterlist *sg, *iter;
> + unsigned int count = view->partial.size;
> + unsigned int offset;
> + int ret = -ENOMEM;
> +
> + st = kmalloc(sizeof(*st), GFP_KERNEL);
> + if (!st)
> + goto err_st_alloc;
> +
> + ret = sg_alloc_table(st, count, GFP_KERNEL);
> + if (ret)
> + goto err_sg_alloc;
> +
> + iter = i915_gem_object_get_sg_dma(obj, view->partial.offset, &offset);
> + GEM_BUG_ON(!iter);
> +
> + sg = st->sgl;
> + st->nents = 0;
> + do {
> + unsigned int len;
> +
> + len = min(sg_dma_len(iter) - (offset << PAGE_SHIFT),
> + count << PAGE_SHIFT);
> + sg_set_page(sg, NULL, len, 0);
> + sg_dma_address(sg) =
> + sg_dma_address(iter) + (offset << PAGE_SHIFT);
> + sg_dma_len(sg) = len;
> +
> + st->nents++;
> + count -= len >> PAGE_SHIFT;
> + if (count == 0) {
> + sg_mark_end(sg);
> + i915_sg_trim(st); /* Drop any unused tail entries. */
> +
> + return st;
> + }
> +
> + sg = __sg_next(sg);
> + iter = __sg_next(iter);
> + offset = 0;
> + } while (1);
> +
> +err_sg_alloc:
> + kfree(st);
> +err_st_alloc:
> + return ERR_PTR(ret);
> +}
> +
> +static int
> +__i915_vma_get_pages(struct i915_vma *vma)
> +{
> + struct sg_table *pages;
> + int ret;
> +
> + /*
> + * The vma->pages are only valid within the lifespan of the borrowed
> + * obj->mm.pages. When the obj->mm.pages sg_table is regenerated, so
> + * must be the vma->pages. A simple rule is that vma->pages must only
> + * be accessed when the obj->mm.pages are pinned.
> + */
> + GEM_BUG_ON(!i915_gem_object_has_pinned_pages(vma->obj));
> +
> + switch (vma->ggtt_view.type) {
> + default:
> + GEM_BUG_ON(vma->ggtt_view.type);
> + fallthrough;
> + case I915_GGTT_VIEW_NORMAL:
> + pages = vma->obj->mm.pages;
> + break;
> +
> + case I915_GGTT_VIEW_ROTATED:
> + pages =
> + intel_rotate_pages(&vma->ggtt_view.rotated, vma->obj);
> + break;
> +
> + case I915_GGTT_VIEW_REMAPPED:
> + pages =
> + intel_remap_pages(&vma->ggtt_view.remapped, vma->obj);
> + break;
> +
> + case I915_GGTT_VIEW_PARTIAL:
> + pages = intel_partial_pages(&vma->ggtt_view, vma->obj);
> + break;
> + }
> +
> + ret = 0;
> + /* gen6 ppgtt doesn't have backing pages, special-case it */
> + if (IS_ERR(pages) && pages != ERR_PTR(-ENODEV)) {

Where does this -ENODEV come from? AFAIK for the gen6 thing mm.pages =
ZERO_SIZE_PTR. Also, just checking, I assume we always hit the
VIEW_NORMAL for that?

> + ret = PTR_ERR(pages);
> + pages = NULL;
> + drm_err(&vma->vm->i915->drm,
> + "Failed to get pages for VMA view type %u (%d)!\n",
> + vma->ggtt_view.type, ret);

Can we just return here?

> + }
> +
> + pages = xchg(&vma->pages, pages);
> +
> + /* did we race against a put_pages? */
> + if (pages && pages != vma->obj->mm.pages) {
> + sg_free_table(vma->pages);
> + kfree(vma->pages);
> + }

What is this race exactly, can we add some more details here please?
So we can more easily evaluate the lockless trickery here.