arm64: Restore forced disabling of KPTI on ThunderX

A noted side-effect of commit 0c6c2d3615ef ("arm64: Generate cpucaps.h")
is that cpucaps are now sorted, changing the enumeration order. This
assumed no dependencies between cpucaps, which turned out not to be true
in one case. UNMAP_KERNEL_AT_EL0 currently needs to be processed after
WORKAROUND_CAVIUM_27456. ThunderX systems are incompatible with KPTI, so
unmap_kernel_at_el0() bails if WORKAROUND_CAVIUM_27456 is set. But because
of the sorting, WORKAROUND_CAVIUM_27456 will not yet have been considered
when unmap_kernel_at_el0() checks for it, so the kernel tries to
run w/ KPTI - and quickly falls over.

Because all ThunderX implementations have homogeneous CPUs, we can remove
this dependency by just checking the current CPU for the erratum.

Fixes: 0c6c2d3615ef ("arm64: Generate cpucaps.h")
Cc: <> # 5.13.x
Signed-off-by: dann frazier <>
Suggested-by: Suzuki K Poulose <>
Reviewed-by: Suzuki K Poulose <>
Reviewed-by: Mark Brown <>
Acked-by: Marc Zyngier <>
Signed-off-by: Catalin Marinas <>
1 file changed