Re: [PATCH v2 1/2] drm/buddy: Prevent BUG_ON by validating rounded allocation

[Arunpravin Paneer Selvam <arunpravin.paneerselvam@amd.com>]

On 20/01/26 16:11, Matthew Auld wrote:
> On 08/01/2026 11:32, Sanjay Yadav wrote:
>> When DRM_BUDDY_CONTIGUOUS_ALLOCATION is set, the requested size is
>> rounded up to the next power-of-two via roundup_pow_of_two().
>> Similarly, for non-contiguous allocations with large min_block_size,
>> the size is aligned up via round_up(). Both operations can produce a
>> rounded size that exceeds mm->size, which later triggers
>> BUG_ON(order > mm->max_order).
>>
>> Example scenarios:
>> - 9G CONTIGUOUS allocation on 10G VRAM memory:
>>    roundup_pow_of_two(9G) = 16G > 10G
>> - 9G allocation with 8G min_block_size on 10G VRAM memory:
>>    round_up(9G, 8G) = 16G > 10G
>>
>> Fix this by checking the rounded size against mm->size. For
>> non-contiguous or range allocations where size > mm->size is invalid,
>> return -EINVAL immediately. For contiguous allocations without range
>> restrictions, allow the request to fall through to the existing
>> __alloc_contig_try_harder() fallback.
>>
>> This ensures invalid user input returns an error or uses the fallback
>> path instead of hitting BUG_ON.
>>
>> v2: (Matt A)
>> - Add Fixes, Cc stable, and Closes tags for context
>>
>> Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/6712
>> Fixes: 0a1844bf0b53 ("drm/buddy: Improve contiguous memory allocation")
>> Cc: <stable@vger.kernel.org> # v6.7+
>> Cc: Christian König <christian.koenig@amd.com>
>> Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
>> Suggested-by: Matthew Auld <matthew.auld@intel.com>
>> Signed-off-by: Sanjay Yadav <sanjay.kumar.yadav@intel.com>
>> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
>> Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
>
> Arun/Christian, when you get a chance could you also merge these two 
> please?

I have merged these 2 patches as well.

Regards,

Arun.

>
>> ---
>>   drivers/gpu/drm/drm_buddy.c | 9 +++++++++
>>   1 file changed, 9 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>> index 2f279b46bd2c..5141348fc6c9 100644
>> --- a/drivers/gpu/drm/drm_buddy.c
>> +++ b/drivers/gpu/drm/drm_buddy.c
>> @@ -1155,6 +1155,15 @@ int drm_buddy_alloc_blocks(struct drm_buddy *mm,
>>       order = fls(pages) - 1;
>>       min_order = ilog2(min_block_size) - ilog2(mm->chunk_size);
>>   +    if (order > mm->max_order || size > mm->size) {
>> +        if ((flags & DRM_BUDDY_CONTIGUOUS_ALLOCATION) &&
>> +            !(flags & DRM_BUDDY_RANGE_ALLOCATION))
>> +            return __alloc_contig_try_harder(mm, original_size,
>> +                             original_min_size, blocks);
>> +
>> +        return -EINVAL;
>> +    }
>> +
>>       do {
>>           order = min(order, (unsigned int)fls(pages) - 1);
>>           BUG_ON(order > mm->max_order);
>