diff mbox series

[1/2] drm: buddy_allocator: Fix buddy allocator init on 32-bit systems

Message ID 20230329065532.2122295-1-davidgow@google.com
State New
Headers
Series [1/2] drm: buddy_allocator: Fix buddy allocator init on 32-bit systems |

Commit Message

David Gow March 29, 2023, 6:55 a.m. UTC 
  The drm buddy allocator tests were broken on 32-bit systems, as
rounddown_pow_of_two() takes a long, and the buddy allocator handles
64-bit sizes even on 32-bit systems.

This can be reproduced with the drm_buddy_allocator KUnit tests on i386:
	./tools/testing/kunit/kunit.py run --arch i386 \
	--kunitconfig ./drivers/gpu/drm/tests drm_buddy

(It results in kernel BUG_ON() when too many blocks are created, due to
the block size being too small.)

This was independently uncovered (and fixed) by Luís Mendes, whose patch
added a new u64 variant of rounddown_pow_of_two(). This version instead
recalculates the size based on the order.

Reported-by: Luís Mendes <luis.p.mendes@gmail.com>
Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@mail.gmail.com/T/
Signed-off-by: David Gow <davidgow@google.com>
---
 drivers/gpu/drm/drm_buddy.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Christian König March 29, 2023, 7:04 a.m. UTC | #1 
Am 29.03.23 um 08:55 schrieb David Gow:
> The drm buddy allocator tests were broken on 32-bit systems, as
> rounddown_pow_of_two() takes a long, and the buddy allocator handles
> 64-bit sizes even on 32-bit systems.
>
> This can be reproduced with the drm_buddy_allocator KUnit tests on i386:
> 	./tools/testing/kunit/kunit.py run --arch i386 \
> 	--kunitconfig ./drivers/gpu/drm/tests drm_buddy
>
> (It results in kernel BUG_ON() when too many blocks are created, due to
> the block size being too small.)
>
> This was independently uncovered (and fixed) by Luís Mendes, whose patch
> added a new u64 variant of rounddown_pow_of_two(). This version instead
> recalculates the size based on the order.
>
> Reported-by: Luís Mendes <luis.p.mendes@gmail.com>
> Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@mail.gmail.com/T/
> Signed-off-by: David Gow <davidgow@google.com>

Acked-by: Christian König <christian.koenig@amd.com> for the series.

> ---
>   drivers/gpu/drm/drm_buddy.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index 3d1f50f481cf..7098f125b54a 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -146,8 +146,8 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>   		unsigned int order;
>   		u64 root_size;
>   
> -		root_size = rounddown_pow_of_two(size);
> -		order = ilog2(root_size) - ilog2(chunk_size);
> +		order = ilog2(size) - ilog2(chunk_size);
> +		root_size = chunk_size << order;
>   
>   		root = drm_block_alloc(mm, NULL, order, offset);
>   		if (!root)
Jani Nikula March 30, 2023, 10:53 a.m. UTC | #2 
On Wed, 29 Mar 2023, David Gow <davidgow@google.com> wrote:
> The drm buddy allocator tests were broken on 32-bit systems, as
> rounddown_pow_of_two() takes a long, and the buddy allocator handles
> 64-bit sizes even on 32-bit systems.
>
> This can be reproduced with the drm_buddy_allocator KUnit tests on i386:
> 	./tools/testing/kunit/kunit.py run --arch i386 \
> 	--kunitconfig ./drivers/gpu/drm/tests drm_buddy
>
> (It results in kernel BUG_ON() when too many blocks are created, due to
> the block size being too small.)
>
> This was independently uncovered (and fixed) by Luís Mendes, whose patch
> added a new u64 variant of rounddown_pow_of_two(). This version instead
> recalculates the size based on the order.
>
> Reported-by: Luís Mendes <luis.p.mendes@gmail.com>
> Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@mail.gmail.com/T/
> Signed-off-by: David Gow <davidgow@google.com>
> ---
>  drivers/gpu/drm/drm_buddy.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
> index 3d1f50f481cf..7098f125b54a 100644
> --- a/drivers/gpu/drm/drm_buddy.c
> +++ b/drivers/gpu/drm/drm_buddy.c
> @@ -146,8 +146,8 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>  		unsigned int order;
>  		u64 root_size;
>  
> -		root_size = rounddown_pow_of_two(size);
> -		order = ilog2(root_size) - ilog2(chunk_size);
> +		order = ilog2(size) - ilog2(chunk_size);
> +		root_size = chunk_size << order;

Just noticed near the beginning of the function there's also:

	if (!is_power_of_2(chunk_size))
		return -EINVAL;

which is also wrong for 32-bit.


BR,
Jani.


>  
>  		root = drm_block_alloc(mm, NULL, order, offset);
>  		if (!root)
Christian König March 30, 2023, 10:56 a.m. UTC | #3 
Am 30.03.23 um 12:53 schrieb Jani Nikula:
> On Wed, 29 Mar 2023, David Gow <davidgow@google.com> wrote:
>> The drm buddy allocator tests were broken on 32-bit systems, as
>> rounddown_pow_of_two() takes a long, and the buddy allocator handles
>> 64-bit sizes even on 32-bit systems.
>>
>> This can be reproduced with the drm_buddy_allocator KUnit tests on i386:
>> 	./tools/testing/kunit/kunit.py run --arch i386 \
>> 	--kunitconfig ./drivers/gpu/drm/tests drm_buddy
>>
>> (It results in kernel BUG_ON() when too many blocks are created, due to
>> the block size being too small.)
>>
>> This was independently uncovered (and fixed) by Luís Mendes, whose patch
>> added a new u64 variant of rounddown_pow_of_two(). This version instead
>> recalculates the size based on the order.
>>
>> Reported-by: Luís Mendes <luis.p.mendes@gmail.com>
>> Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@mail.gmail.com/T/
>> Signed-off-by: David Gow <davidgow@google.com>
>> ---
>>   drivers/gpu/drm/drm_buddy.c | 4 ++--
>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>> index 3d1f50f481cf..7098f125b54a 100644
>> --- a/drivers/gpu/drm/drm_buddy.c
>> +++ b/drivers/gpu/drm/drm_buddy.c
>> @@ -146,8 +146,8 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>>   		unsigned int order;
>>   		u64 root_size;
>>   
>> -		root_size = rounddown_pow_of_two(size);
>> -		order = ilog2(root_size) - ilog2(chunk_size);
>> +		order = ilog2(size) - ilog2(chunk_size);
>> +		root_size = chunk_size << order;
> Just noticed near the beginning of the function there's also:
>
> 	if (!is_power_of_2(chunk_size))
> 		return -EINVAL;
>
> which is also wrong for 32-bit.

Yeah, but that isn't vital. We just use u64 for the chunk_size for 
consistency.

In reality I wouldn't except more than 256K here.

Regards,
Christian.

>
>
> BR,
> Jani.
>
>
>>   
>>   		root = drm_block_alloc(mm, NULL, order, offset);
>>   		if (!root)
Jani Nikula March 30, 2023, 11:12 a.m. UTC | #4 
On Thu, 30 Mar 2023, Christian König <christian.koenig@amd.com> wrote:
> Am 30.03.23 um 12:53 schrieb Jani Nikula:
>> On Wed, 29 Mar 2023, David Gow <davidgow@google.com> wrote:
>>> The drm buddy allocator tests were broken on 32-bit systems, as
>>> rounddown_pow_of_two() takes a long, and the buddy allocator handles
>>> 64-bit sizes even on 32-bit systems.
>>>
>>> This can be reproduced with the drm_buddy_allocator KUnit tests on i386:
>>> 	./tools/testing/kunit/kunit.py run --arch i386 \
>>> 	--kunitconfig ./drivers/gpu/drm/tests drm_buddy
>>>
>>> (It results in kernel BUG_ON() when too many blocks are created, due to
>>> the block size being too small.)
>>>
>>> This was independently uncovered (and fixed) by Luís Mendes, whose patch
>>> added a new u64 variant of rounddown_pow_of_two(). This version instead
>>> recalculates the size based on the order.
>>>
>>> Reported-by: Luís Mendes <luis.p.mendes@gmail.com>
>>> Link: https://lore.kernel.org/lkml/CAEzXK1oghXAB_KpKpm=-CviDQbNaH0qfgYTSSjZgvvyj4U78AA@mail.gmail.com/T/
>>> Signed-off-by: David Gow <davidgow@google.com>
>>> ---
>>>   drivers/gpu/drm/drm_buddy.c | 4 ++--
>>>   1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
>>> index 3d1f50f481cf..7098f125b54a 100644
>>> --- a/drivers/gpu/drm/drm_buddy.c
>>> +++ b/drivers/gpu/drm/drm_buddy.c
>>> @@ -146,8 +146,8 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
>>>   		unsigned int order;
>>>   		u64 root_size;
>>>   
>>> -		root_size = rounddown_pow_of_two(size);
>>> -		order = ilog2(root_size) - ilog2(chunk_size);
>>> +		order = ilog2(size) - ilog2(chunk_size);
>>> +		root_size = chunk_size << order;
>> Just noticed near the beginning of the function there's also:
>>
>> 	if (!is_power_of_2(chunk_size))
>> 		return -EINVAL;
>>
>> which is also wrong for 32-bit.
>
> Yeah, but that isn't vital. We just use u64 for the chunk_size for 
> consistency.
>
> In reality I wouldn't except more than 256K here.

Right. It's just not pedantically correct either. ;)

is_power_of_2() is pretty scary as it is, since it just truncates.

BR,
Jani.


>
> Regards,
> Christian.
>
>>
>>
>> BR,
>> Jani.
>>
>>
>>>   
>>>   		root = drm_block_alloc(mm, NULL, order, offset);
>>>   		if (!root)
>
diff mbox series

Patch

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index 3d1f50f481cf..7098f125b54a 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -146,8 +146,8 @@  int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
 		unsigned int order;
 		u64 root_size;
 
-		root_size = rounddown_pow_of_two(size);
-		order = ilog2(root_size) - ilog2(chunk_size);
+		order = ilog2(size) - ilog2(chunk_size);
+		root_size = chunk_size << order;
 
 		root = drm_block_alloc(mm, NULL, order, offset);
 		if (!root)