Re: [PATCH] drm/amd/display: use kvzalloc to allocate struct dc

[Mario Limonciello <superm1@kernel.org>]

On 6/22/26 23:56, Honglei Huang wrote:
> struct dc has grown large over time (most of it the two inlined
> dc_scratch_space copies) and now sits close to the page allocator's 4 MiB
> contiguous allocation limit. Its actual size is not fixed by the source
> alone, it also depends on the compiler and the .configk, so it can
> easily cross 4 MiB, e.g. with a newer GCC or a config change, and once it
> does dc_create() fails.
> 
> dc_create() allocates it with kzalloc(). Once struct dc exceeds 4 MiB the
> request is rounded up to order 11 (8 MiB), which is above MAX_PAGE_ORDER,
> so the page allocator warns and returns NULL. dc_create() then fails, DM
> init fails and amdgpu probe aborts with -EINVAL:
> 
>    WARNING: mm/page_alloc.c:5197 at __alloc_frozen_pages_noprof+0x2f9/0x380
>    RSI: ...000b   RBP: ...000b      <- order = 11 (8 MiB)
>     __kmalloc_large_noprof+0x1e/0xc0
>     dc_create+0x38/0x660 [amdgpu]
>     amdgpu_dm_init+0x2d9/0x510 [amdgpu]
>     dm_hw_init+0x1b/0x90 [amdgpu]
>    amdgpu 0000:03:00.0: hw_init of IP block <dm> failed -22
>    amdgpu 0000:03:00.0: probe with driver amdgpu failed with error -22
> 
> struct dc is software only state, never DMAed and only kept as an opaque
> pointer, so it needs no physically contiguous memory. Use kvzalloc()/
> kvfree() so it falls back to vmalloc(), removing the dependency on
> MAX_PAGE_ORDER. The underlying bloat of struct dc should be addressed
> separately.
> 

Cc: stable@vger.kernel.org
Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
Closes: https://gitlab.freedesktop.org/drm/amd/-/work_items/5406

> Signed-off-by: Honglei Huang <honghuan@amd.com>
> ---
>   drivers/gpu/drm/amd/display/dc/core/dc.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/core/dc.c b/drivers/gpu/drm/amd/display/dc/core/dc.c
> index b3530fbf32f..65bd927435e 100644
> --- a/drivers/gpu/drm/amd/display/dc/core/dc.c
> +++ b/drivers/gpu/drm/amd/display/dc/core/dc.c
> @@ -1507,7 +1507,7 @@ static void disable_vbios_mode_if_required(
>   
>   struct dc *dc_create(const struct dc_init_data *init_params)
>   {
> -	struct dc *dc = kzalloc_obj(*dc);
> +	struct dc *dc = kvzalloc_obj(*dc);
>   	unsigned int full_pipe_count;
>   
>   	if (!dc)
> @@ -1555,7 +1555,7 @@ struct dc *dc_create(const struct dc_init_data *init_params)
>   
>   destruct_dc:
>   	dc_destruct(dc);
> -	kfree(dc);
> +	kvfree(dc);
>   	return NULL;
>   }
>   
> @@ -1604,7 +1604,7 @@ void dc_deinit_callbacks(struct dc *dc)
>   void dc_destroy(struct dc **dc)
>   {
>   	dc_destruct(*dc);
> -	kfree(*dc);
> +	kvfree(*dc);
>   	*dc = NULL;
>   }
>