Re: [PATCH v3 6/6] arm64/mm: Drop configurable 48-bit physical address space limit

Hi Ard,

On 12/12/2024 16:18, Ard Biesheuvel wrote:

From: Ard Biesheuvel <ardb@kernel.org>

Currently, the maximum supported physical address space can be
configured as either 48 bits or 52 bits. The only remaining difference
between these in practice is that the former omits the masking and
shifting required to construct TTBR and PTE values, which carry bits #48
and higher disjoint from the rest of the physical address.

The overhead of performing these additional calculations is negligible,
and so there is little reason to retain support for two different
configurations, and we can simply support whatever the hardware
supports.

I am seeing a boot failure on Apple iPad 7 which uses 
CONFIG_ARM64_16K=y after this change in linux-next as commit
32d053d6f5e9, with nothing appearing on serial console with
earlycon enabled unless I set CONFIG_ARM64_VA_BITS_52=y. Reverting
this patch makes the kernel work again.

Nick Chan