arm64: mm: avoid redundant READ_ONCE(*ptep)

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In set_pte_at(), we read the old pte value so that it can be passed into
checks for racy hw updates. These checks are only performed for
CONFIG_DEBUG_VM, and the value is not used otherwise.

Since we read the pte value with READ_ONCE(), the compiler cannot elide
the redundant read for !CONFIG_DEBUG_VM kernels.

Let's ameliorate matters by moving the read and the checks into a
helper, __check_racy_pte_update(), which only performs the read when the
value will be used. This also allows us to reformat the conditions for
clarity.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

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Mark Rutland 2019-06-10 13:41:07 +01:00 • committed by Catalin Marinas

parent 4745224b45

commit 9b60472205

1 changed files with 30 additions and 17 deletions

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arch/arm64/include/asm/pgtable.h

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