arm64/mm: Fix Boot panic on Ampere Altra

When the range of present physical memory is sufficiently small enough
and the reserved address space for the linear map is sufficiently large
enough, The linear map base address is randomized in
arm64_memblock_init().

Prior to commit 62cffa49 ("arm64/mm: Override PARange for !LPA2 and
use it consistently"), we decided if the sizes were suitable with the
help of the raw mmfr0.parange. But the commit changed this to use the
sanitized version instead. But the function runs before the register has
been sanitized so this returns 0, interpreted as a parange of 32 bits.
Some fun wrapping occurs and the logic concludes that there is enough
room to randomize the linear map base address, when really there isn't.
So the top of the linear map ends up outside the reserved address space.

Since the PA range cannot be overridden in the first place, restore the
mmfr0 reading logic to its state prior to 62cffa49, where the raw
register value is used.

Reported-by: Luiz Capitulino <luizcap@redhat.com>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Closes: https://lore.kernel.org/all/a3d9acbe-07c2-43b6-9ba9-a7585f770e83@redhat.com/


Fixes: 62cffa49 ("arm64/mm: Override PARange for !LPA2 and use it consistently")
Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
Link: https://lore.kernel.org/r/20250225114638.2038006-1-ryan.roberts@arm.com


Cc: stable@vger.kernel.org
Signed-off-by: Will Deacon <will@kernel.org>