On Thu, Sep 17, 2026 at 02:33:43PM +0200, Boris Brezillon wrote:
> The check on the folio size is actually moot if the BO offset matching
> the VA we're checking huge-mapping for is not 2M aligned as well.
> This means that we are sometimes returning true when we shouldn't, which
> forces an extra unmap+map to deal with block-mapping splits. It's not
> a functional bug per-se, because the unmap+map sequence will restore
> things in the state we expect them to be, but it's better to properly
> optimize those cases.
>
> Note that we now align the VA on 2M address below it otherwise we can't
> check the bo_offset alignment (both physical and virtual address need
> to be aligned, in addition to the physically contiguous size being 2M,
> which the folio size check ensures).
>
> These changes force us to pass the drm_gpuva that's being unmapped
> instead of the new mappings that will be created to cover the left/right
> sections we remap. This changes makes the logic a lot easier to reason
> about, because it doesn't make sense to how things were mapped by
> passing the new mappings that are not yet in place.
>
> Fixes: 8e7460eac786 ("drm/panthor: Support partial unmaps of huge pages")
> Signed-off-by: Boris Brezillon <[email protected]>
Reviewed-by: Liviu Dudau <[email protected]>
Best regards,
Liviu
> ---
> drivers/gpu/drm/panthor/panthor_mmu.c | 24 +++++++++++++++++++-----
> 1 file changed, 19 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/panthor/panthor_mmu.c
> b/drivers/gpu/drm/panthor/panthor_mmu.c
> index 9f63a048df61..b0a7033480e6 100644
> --- a/drivers/gpu/drm/panthor/panthor_mmu.c
> +++ b/drivers/gpu/drm/panthor/panthor_mmu.c
> @@ -2295,15 +2295,29 @@ static int panthor_gpuva_sm_step_map(struct
> drm_gpuva_op *op, void *priv)
> }
>
> static bool
> -iova_mapped_as_huge_page(struct drm_gpuva_op_map *op, u64 addr)
> +iova_mapped_as_huge_page(struct drm_gpuva *mapping, u64 va)
> {
> - struct panthor_gem_object *bo = to_panthor_bo(op->gem.obj);
> + struct panthor_gem_object *bo = to_panthor_bo(mapping->gem.obj);
> + u64 aligned_va = ALIGN_DOWN(va, SZ_2M);
> const struct page *pg;
> pgoff_t bo_offset;
>
> - bo_offset = addr - op->va.addr + op->gem.offset;
> + /* If the 2M-aligned VA is outside the mapping being tested, we know
> + * it's not a huge map.
> + */
> + if (aligned_va < mapping->va.addr)
> + return false;
> +
> + bo_offset = aligned_va - mapping->va.addr + mapping->gem.offset;
> pg = bo->backing.pages[bo_offset >> PAGE_SHIFT];
>
> + /* In case of shmem backing, we know we can only have a huge mapping
> + * if the bo_offset is 2M aligned, meaning we can skip the folio size
> + * check if it's not the case.
> + */
> + if (!IS_ALIGNED(bo_offset, SZ_2M))
> + return false;
> +
> return folio_size(page_folio(pg)) >= SZ_2M;
> }
>
> @@ -2328,7 +2342,7 @@ unmap_hugepage_align(const struct drm_gpuva_op_remap
> *op,
> */
> if (op->prev && aligned_unmap_start < *unmap_start &&
> op->prev->va.addr <= aligned_unmap_start &&
> - (is_sparse || iova_mapped_as_huge_page(op->prev, *unmap_start))) {
> + (is_sparse || iova_mapped_as_huge_page(op->unmap->va,
> *unmap_start))) {
> *unmap_range += *unmap_start - aligned_unmap_start;
> *unmap_start = aligned_unmap_start;
> }
> @@ -2338,7 +2352,7 @@ unmap_hugepage_align(const struct drm_gpuva_op_remap
> *op,
> */
> if (op->next && aligned_unmap_end > unmap_end &&
> op->next->va.addr + op->next->va.range >= aligned_unmap_end &&
> - (is_sparse || iova_mapped_as_huge_page(op->next, unmap_end - 1))) {
> + (is_sparse || iova_mapped_as_huge_page(op->unmap->va, unmap_end -
> 1))) {
> *unmap_range += aligned_unmap_end - unmap_end;
> }
> }
>
> --
> 2.55.0
>
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
