arm64: Document sysctls for emulated deprecated instructions (dd720784) · Commits · 戴 / test

We have support for emulating a number of deprecated instructions in the kernel with individual Kconfig options enabling this support per instruction. In addition to the Kconfig options we also provide runtime control via sysctls but this is not currently mentioned in the Kconfig so not very discoverable for users. This is particularly important for SWP/SWPB since this is disabled by default at runtime and must be enabled via the sysctl, causing considerable frustration for users who have enabled the config option and are then confused to find that the instruction is still faulting. Add a reference to the sysctls in the help text for each of the config options, noting that SWP/SWPB is disabled by default, to improve the user experience. Signed-off-by:

Mark Brown <broonie@kernel.org> Link: https://lore.kernel.org/r/20200625131507.32334-1-broonie@kernel.org Signed-off-by:

Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

+6 −2

Original line number	Diff line number	Diff line
		@@ -1327,6 +1327,8 @@ config SWP_EMULATION
		ARMv8 obsoletes the use of A32 SWP/SWPB instructions such that
		they are always undefined. Say Y here to enable software
		emulation of these instructions for userspace using LDXR/STXR.
		This feature can be controlled at runtime with the abi.swp
		sysctl which is disabled by default.

		In some older versions of glibc [<=2.8] SWP is used during futex
		trylock() operations with the assumption that the code will not
		@@ -1353,7 +1355,8 @@ config CP15_BARRIER_EMULATION
		Say Y here to enable software emulation of these
		instructions for AArch32 userspace code. When this option is
		enabled, CP15 barrier usage is traced which can help
		identify software that needs updating.
		identify software that needs updating. This feature can be
		controlled at runtime with the abi.cp15_barrier sysctl.

		If unsure, say Y

		@@ -1364,7 +1367,8 @@ config SETEND_EMULATION
		AArch32 EL0, and is deprecated in ARMv8.

		Say Y here to enable software emulation of the instruction
		for AArch32 userspace code.
		for AArch32 userspace code. This feature can be controlled
		at runtime with the abi.setend sysctl.

		Note: All the cpus on the system must have mixed endian support at EL0
		for this feature to be enabled. If a new CPU - which doesn't support mixed

Admin message