linux/arch/arm64/lib
Mark Rutland 4c73056e32 arm64: Avoid cpus_have_const_cap() for ARM64_HAS_WFXT
In __delay() we use cpus_have_const_cap() to check for ARM64_HAS_WFXT,
but this is not necessary and alternative_has_cap() would be preferable.

For historical reasons, cpus_have_const_cap() is more complicated than
it needs to be. Before cpucaps are finalized, it will perform a bitmap
test of the system_cpucaps bitmap, and once cpucaps are finalized it
will use an alternative branch. This used to be necessary to handle some
race conditions in the window between cpucap detection and the
subsequent patching of alternatives and static branches, where different
branches could be out-of-sync with one another (or w.r.t. alternative
sequences). Now that we use alternative branches instead of static
branches, these are all patched atomically w.r.t. one another, and there
are only a handful of cases that need special care in the window between
cpucap detection and alternative patching.

Due to the above, it would be nice to remove cpus_have_const_cap(), and
migrate callers over to alternative_has_cap_*(), cpus_have_final_cap(),
or cpus_have_cap() depending on when their requirements. This will
remove redundant instructions and improve code generation, and will make
it easier to determine how each callsite will behave before, during, and
after alternative patching.

The cpus_have_const_cap() check in __delay() is an optimization to use
WFIT and WFET in preference to busy-polling the counter and/or using
regular WFE and relying upon the architected timer event stream. It is
not necessary to apply this optimization in the window between detecting
the ARM64_HAS_WFXT cpucap and patching alternatives.

This patch replaces the use of cpus_have_const_cap() with
alternative_has_cap_unlikely(), which will avoid generating code to test
the system_cpucaps bitmap and should be better for all subsequent calls
at runtime.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
2023-10-16 14:17:05 +01:00
..
clear_page.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
clear_user.S arm64: extable: consolidate definitions 2021-10-21 10:45:22 +01:00
copy_from_user.S arm64: lib: __arch_copy_from_user(): fold fixups into body 2021-10-21 10:45:21 +01:00
copy_page.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
copy_template.S treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 234 2019-06-19 17:09:07 +02:00
copy_to_user.S arm64: lib: __arch_copy_to_user(): fold fixups into body 2021-10-21 10:45:21 +01:00
crc32.S arm64: lib: accelerate crc32_be 2022-01-31 11:21:43 +11:00
csum.c arm64: csum: Fix OoB access in IP checksum code for negative lengths 2023-09-07 10:15:20 +01:00
delay.c arm64: Avoid cpus_have_const_cap() for ARM64_HAS_WFXT 2023-10-16 14:17:05 +01:00
error-inject.c arm64: Add support for function error injection 2019-08-07 13:53:09 +01:00
insn.c arm64: insn: Add encoders for LDRSB/LDRSH/LDRSW 2023-08-18 15:45:34 +02:00
kasan_sw_tags.S arm64: Use BTI C directly and unconditionally 2021-12-14 18:12:58 +00:00
Makefile isystem: delete global -isystem compile option 2021-09-22 09:26:24 +09:00
memchr.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
memcmp.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
memcpy.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
memset.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
mte.S arm64/sysreg: Remove duplicate definitions from asm/sysreg.h 2022-12-01 17:31:12 +00:00
strchr.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
strcmp.S Merge branch 'for-next/strings' into for-next/core 2022-03-14 19:02:52 +00:00
strlen.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
strncmp.S Merge branch 'for-next/strings' into for-next/core 2022-03-14 19:02:52 +00:00
strnlen.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
strrchr.S arm64: clean up symbol aliasing 2022-02-22 16:21:34 +00:00
tishift.S arm64: lib: Use modern annotations for assembly functions 2020-01-08 12:23:02 +00:00
uaccess_flushcache.c arm: uaccess: Remove memcpy_page_flushcache() 2023-03-27 16:26:19 +01:00
xor-neon.c arm64: xor-neon: mark xor_arm64_neon_*() static 2023-05-25 17:44:01 +01:00