Re: [PATCH] iommu/arm-smmu-v3: Fix L1 stream table index calculation for AmpereOne

[Yang Shi]

On 10/1/24 11:27 AM, Nicolin Chen wrote:
> On Tue, Oct 01, 2024 at 11:03:46AM -0700, Yang Shi wrote:
> > Using 64 bit immediate when doing shift can solve the problem.  The
> > disssembly after the fix looks like:
> [...]
>
> >          unsigned int last_sid_idx =
> > -               arm_smmu_strtab_l1_idx((1 << smmu->sid_bits) - 1);
> > +               arm_smmu_strtab_l1_idx((1UL << smmu->sid_bits) - 1);
> Could a 32-bit build be a corner case where UL is no longer a
> "64 bit" stated in the commit message?

It shouldn't. Because smmu v3 depends on ARM64.

config ARM_SMMU_V3
        tristate "ARM Ltd. System MMU Version 3 (SMMUv3) Support"
        depends on ARM64

> Also, there are other places doing "1 << smmu->sid_bits", e.g.
> arm_smmu_init_strtab_linear().

The disassembly shows it uses "sbfiz   x21, x20, 6, 32" instead of lsl. 
1UL should be used if we want to take extra caution and don't prefer 
rely on compiler.

> Then, can ssid_bits/s1cdmax be a concern similarly?

IIUC, ssid_bits is determined by IDR1_SSIDSIZE. It is GENMASK(10, 6). So 
it shouldn't be 32. IDR1_SIDSIZE is GENMASK(5, 0).

> Thanks
> Nicolin