IOMMU guest VA space fix

[br]

Summary

currently, iommu gas could not allocate a guest VA.
setting domain->end to BUS_SPACE_MAXADDR resolve the issue, but the hardware does not fully support BUS_SPACE_MAXADDR range.
So we are currently trying to limit space to 48 or 52 bit based on hardware capabilities.

[andrew]

Having looked at it again we should ask the SMMU the maximum virtual address it supports. On the SMMUv3 it is the SMMU_IDR5.VAX field to decide if it's a 48 or 52 bit address space.

[br]

it does not seem to work with 52 bit

+       if (sc->features & SMMU_FEATURE_VAX)
+               iodom->end = MAXADDR_52BIT;
+       else
+               iodom->end = MAXADDR_48BIT;

[br]

set maxaddr correctly in tag and domain->end

[andrew]

sys/arm64/iommu/smmu.c

1752

I would skip the VAX check and only use the 48-bit option. We can only use 52-bit with a 64k IOMMU PAGE_SIZE

[br]

Use 48-bit address space regardless of VAX bit