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>> 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