[v2 PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for 32-bit sid size
Yang Shi
yang at os.amperecomputing.com
Thu Oct 3 08:31:23 PDT 2024
On 10/3/24 4:16 AM, Jason Gunthorpe wrote:
> On Wed, Oct 02, 2024 at 01:05:08PM -0700, Yang Shi wrote:
>>> It would make some sense to have something like:
>>>
>>> u64 size = arm_smmu_strtab_max_sid()
>>>
>>> /* Would require too much memory */
>>> if (size > SZ_512M)
>>> return -EINVAL;
>> Why not just check smmu->sid_bits?
>>
>> For example,
>>
>> if (smmu->sid_bits > 28)
>> return -EINVAL;
>>
>> The check can happen before the shift.
> Sure, but IMHO it reads a bit better to check the size computed from
> the helper
>
> MAX_PAGE_ORDER is often 10, so kmalloc will always fail before we
> reach 28 bits of sid space.
I'm wondering we may just use 31 instead of using some magic number:
if (smmu->sid_bits > 31)
return -EINVAL;
If I understand correctly, the check is mainly used to avoid the u64 ->
u32 overflow. This check guarantee no overflow. If some crazy hardware
really requests that large memory, the allocation will fail.
>
> Jason
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