Re: [RFC PATCH V6 2/7] drm/gpu: Add gpu_buddy_addr_to_block helper

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Mar 27, 2026 at 05:18:15PM +0530, Tejas Upadhyay wrote:
> Add helper with primary purpose is to efficiently trace a specific
> physical memory address back to its corresponding TTM buffer object.
> 
> Signed-off-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
> ---
>  drivers/gpu/buddy.c       | 56 +++++++++++++++++++++++++++++++++++++++
>  include/linux/gpu_buddy.h |  2 ++
>  2 files changed, 58 insertions(+)
> 
> diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c
> index 52686672e99f..2d26c2a0f971 100644
> --- a/drivers/gpu/buddy.c
> +++ b/drivers/gpu/buddy.c
> @@ -589,6 +589,62 @@ void gpu_buddy_free_block(struct gpu_buddy *mm,
>  }
>  EXPORT_SYMBOL(gpu_buddy_free_block);
>  
> +/**
> + * gpu_buddy_addr_to_block - given physical address find a block
> + *
> + * @mm: GPU buddy manager
> + * @addr: Physical address
> + *
> + * Returns:
> + * gpu_buddy_block on success, NULL or error code on failure
> + */
> +struct gpu_buddy_block *gpu_buddy_addr_to_block(struct gpu_buddy *mm, u64 addr)
> +{
> +	struct gpu_buddy_block *block;
> +	LIST_HEAD(dfs);
> +	u64 end;
> +	int i;
> +

This is somewhat of an orthogonal issue, but we really should update
gpu_buddy so drivers can register a lock that we can assert is held in
functions where gpu_buddy manipulates blocks.

Something like this [1].

I’ll defer to the gpu_buddy maintainers on whether this code is correct.

Matt

[1] https://elixir.bootlin.com/linux/v6.19.10/source/include/drm/drm_gpusvm.h#L341

> +	end = addr + SZ_4K - 1;
> +	for (i = 0; i < mm->n_roots; ++i)
> +		list_add_tail(&mm->roots[i]->tmp_link, &dfs);
> +
> +	do {
> +		u64 block_start;
> +		u64 block_end;
> +
> +		block = list_first_entry_or_null(&dfs,
> +						 struct gpu_buddy_block,
> +						 tmp_link);
> +		if (!block)
> +			break;
> +
> +		list_del(&block->tmp_link);
> +
> +		block_start = gpu_buddy_block_offset(block);
> +		block_end = block_start + gpu_buddy_block_size(mm, block) - 1;
> +
> +		if (!overlaps(addr, end, block_start, block_end))
> +			continue;
> +
> +		if (contains(addr, end, block_start, block_end) &&
> +		    !gpu_buddy_block_is_split(block)) {
> +			if (gpu_buddy_block_is_free(block))
> +				return NULL;
> +			else if (gpu_buddy_block_is_allocated(block) && !mm->clear_avail)
> +				return block;
> +		}
> +
> +		if (gpu_buddy_block_is_split(block)) {
> +			list_add(&block->right->tmp_link, &dfs);
> +			list_add(&block->left->tmp_link, &dfs);
> +		}
> +	} while (1);
> +
> +	return ERR_PTR(-ENXIO);
> +}
> +EXPORT_SYMBOL(gpu_buddy_addr_to_block);
> +
>  static void __gpu_buddy_free_list(struct gpu_buddy *mm,
>  				  struct list_head *objects,
>  				  bool mark_clear,
> diff --git a/include/linux/gpu_buddy.h b/include/linux/gpu_buddy.h
> index 5fa917ba5450..957c69c560bc 100644
> --- a/include/linux/gpu_buddy.h
> +++ b/include/linux/gpu_buddy.h
> @@ -231,6 +231,8 @@ void gpu_buddy_reset_clear(struct gpu_buddy *mm, bool is_clear);
>  
>  void gpu_buddy_free_block(struct gpu_buddy *mm, struct gpu_buddy_block *block);
>  
> +struct gpu_buddy_block *gpu_buddy_addr_to_block(struct gpu_buddy *mm, u64 addr);
> +
>  void gpu_buddy_free_list(struct gpu_buddy *mm,
>  			 struct list_head *objects,
>  			 unsigned int flags);
> -- 
> 2.52.0
>