arm64: Mask all exceptions during kernel_exit

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To take RAS Exceptions as quickly as possible we need to keep SError
unmasked as much as possible. We need to mask it during kernel_exit
as taking an error from this code will overwrite the exception-registers.

Adding a naked 'disable_daif' to kernel_exit causes a performance problem
for micro-benchmarks that do no real work, (e.g. calling getpid() in a
loop). This is because the ret_to_user loop has already masked IRQs so
that the TIF_WORK_MASK thread flags can't change underneath it, adding
disable_daif is an additional self-synchronising operation.

In the future, the RAS APEI code may need to modify the TIF_WORK_MASK
flags from an SError, in which case the ret_to_user loop must mask SError
while it examines the flags.

Disable all exceptions for return to EL1. For return to EL0 get the
ret_to_user loop to leave all exceptions masked once it has done its
work, this avoids an extra pstate-write.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Julien Thierry <julien.thierry@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

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James Morse 2017-11-02 12:12:37 +00:00 • committed by Will Deacon

parent 41bd5b5d22

commit 8d66772e86

2 changed files with 11 additions and 7 deletions

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10

arch/arm64/kernel/entry.S

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8

arch/arm64/kernel/signal.c

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