Hi Lukas,
Le mer., déc. 8 2021 at 12:43:00 +0100, Lukas Bulwahn
<lukas.bulwahn@xxxxxxxxx> a écrit :
Dear Daniel, dear Paul, dear Thomas,
In commit d4a451d5fc84 ("arch: remove the ARCH_PHYS_ADDR_T_64BIT
config symbol") from April 2018, the config ARCH_PHYS_ADDR_T_64BIT was
removed and all instances of that config were refactored
appropriately. Since then, it is recommended to use the config
PHYS_ADDR_T_64BIT instead.
Then in June 2019, commit 171543e75272 ("MIPS: Disallow
CPU_SUPPORTS_HUGEPAGES for XPA,EVA") introduces the expression
"!(32BIT && (ARCH_PHYS_ADDR_T_64BIT || EVA))" for config
CPU_SUPPORTS_HUGEPAGES, which refers to the non-existing symbol
ARCH_PHYS_ADDR_T_64BIT.
In this expression, the symbol ARCH_PHYS_ADDR_T_64BIT always evaluates
to false. So, the expression is effectively "!(32BIT && EVA)" right
now.
Now, it is a bit unclear what is intended here, especially since it
was not noticed to be wrong for the last two years:
- The commit is buggy, but nobody noticed it so far. It was intended
to refer to PHYS_ADDR_T_64BIT. We need to provide a fix that changes
the semantics by referring to the intended Kconfig symbol.
It should be PHYS_ADDR_T_64BIT, yes.
- The commit is just a bit unclean and that is why nobody noticed. The
reference to ARCH_PHYS_ADDR_T_64BIT can be dropped. We can provide a
clean-up patch that preserves the current semantics.
AFAIK hugepages still don't work as-is on 32-bit as we are running out
of available bits in PTEs. I do have hugepages enabled on a kernel
build, but I have to manually disable ARCH_HAS_PTE_SPECIAL and
CPU_HAS_RIXI to free up space. This is annoying but not something that
can be fixed easily.
-Paul
Once the situation for that commit and its intention is clear, I am
happy to provide the suitable patch.
Best regards,
Lukas
