arm64: Prevent offlining first CPU with 32-bit EL0 on mismatched system

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If we want to support 32-bit applications, then when we identify a CPU
with mismatched 32-bit EL0 support we must ensure that we will always
have an active 32-bit CPU available to us from then on. This is important
for the scheduler, because is_cpu_allowed() will be constrained to 32-bit
CPUs for compat tasks and forced migration due to a hotplug event will
hang if no 32-bit CPUs are available.

On detecting a mismatch, prevent offlining of either the mismatching CPU
if it is 32-bit capable, or find the first active 32-bit capable CPU
otherwise.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210730112443.23245-13-will@kernel.org

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Will Deacon 2021-07-30 12:24:39 +01:00 • committed by Peter Zijlstra

parent 08cd8f4112

commit df950811f4

1 changed files with 24 additions and 1 deletions

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arch/arm64/kernel/cpufeature.c

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