kernel/linux.git/arch/arm64/include/asm/lse.h, branch linux-7.0.y

arm64: Unconditionally enable LSE support

2026-01-22T10:16:41+00:00

LSE atomics have been in the architecture since ARMv8.1 (released in 2014), and are hopefully supported by all modern toolchains. Drop the optional nature of LSE support in the kernel, and always compile the support in, as this really is very little code. LL/SC still is the default, and the switch to LSE is done dynamically. Signed-off-by: Marc Zyngier Signed-off-by: Will Deacon

arm64: Remove system_uses_lse_atomics()

2023-10-18T09:58:59+00:00

There are two variants of system_uses_lse_atomics(), depending on CONFIG_ARM64_LSE_ATOMICS. The function isn't called anywhere when CONFIG_ARM64_LSE_ATOMICS is disabled. It can be directly replaced by alternative_has_cap_likely(ARM64_HAS_LSE_ATOMICS) when the kernel option is enabled. No need to keep system_uses_lse_atomics() and just remove it. Signed-off-by: Gavin Shan Acked-by: Mark Rutland Link: https://lore.kernel.org/r/20231017005036.334067-1-gshan@redhat.com Signed-off-by: Catalin Marinas

arm64: alternatives: use cpucap naming

2023-06-07T16:57:47+00:00

To more clearly align the various users of the cpucap enumeration, this patch changes the alternative code to use the term `cpucap` in favour of `feature`. The alternative_has_feature_{likely,unlikely}() functions are renamed to alternative_has_cap_ Reviewed-by: Suzuki K Poulose Cc: Marc Zyngier Cc: Mark Brown Cc: Will Deacon Link: https://lore.kernel.org/r/20230607164846.3967305-3-mark.rutland@arm.com Signed-off-by: Catalin Marinas

arm64: atomics: lse: remove stale dependency on JUMP_LABEL

2022-11-14T14:44:14+00:00

Currently CONFIG_ARM64_USE_LSE_ATOMICS depends upon CONFIG_JUMP_LABEL, as the inline atomics were indirected with a static branch. However, since commit: 21fb26bfb01ffe0d ("arm64: alternatives: add alternative_has_feature_*()") ... we use an alternative_branch (which is always available) rather than a static branch, and hence the dependency is unnecessary. Remove the stale dependency, along with the stale include. This will allow the use of LSE atomics in kernels built with CONFIG_JUMP_LABEL=n, and reduces the risk of circular header dependencies via . Signed-off-by: Mark Rutland Cc: Catalin Marinas Cc: Will Deacon Link: https://lore.kernel.org/r/20221114125424.2998268-1-mark.rutland@arm.com Signed-off-by: Will Deacon

arm64: alternatives: add alternative_has_feature_*()

2022-09-16T16:15:03+00:00

Currrently we use a mixture of alternative sequences and static branches to handle features detected at boot time. For ease of maintenance we generally prefer to use static branches in C code, but this has a few downsides: * Each static branch has metadata in the __jump_table section, which is not discarded after features are finalized. This wastes some space, and slows down the patching of other static branches. * The static branches are patched at a different point in time from the alternatives, so changes are not atomic. This leaves a transient period where there could be a mismatch between the behaviour of alternatives and static branches, which could be problematic for some features (e.g. pseudo-NMI). * More (instrumentable) kernel code is executed to patch each static branch, which can be risky when patching certain features (e.g. irqflags management for pseudo-NMI). * When CONFIG_JUMP_LABEL=n, static branches are turned into a load of a flag and a conditional branch. This means it isn't safe to use such static branches in an alternative address space (e.g. the NVHE/PKVM hyp code), where the generated address isn't safe to acccess. To deal with these issues, this patch introduces new alternative_has_feature_*() helpers, which work like static branches but are patched using alternatives. This ensures the patching is performed at the same time as other alternative patching, allows the metadata to be freed after patching, and is safe for use in alternative address spaces. Note that all supported toolchains have asm goto support, and since commit: a0a12c3ed057af57 ("asm goto: eradicate CC_HAS_ASM_GOTO)" ... the CC_HAS_ASM_GOTO Kconfig symbol has been removed, so no feature check is necessary, and we can always make use of asm goto. Additionally, note that: * This has no impact on cpus_have_cap(), which is a dynamic check. * This has no functional impact on cpus_have_const_cap(). The branches are patched slightly later than before this patch, but these branches are not reachable until caps have been finalised. * It is now invalid to use cpus_have_final_cap() in the window between feature detection and patching. All existing uses are only expected after patching anyway, so this should not be a problem. * The LSE atomics will now be enabled during alternatives patching rather than immediately before. As the LL/SC an LSE atomics are functionally equivalent this should not be problematic. When building defconfig with GCC 12.1.0, the resulting Image is 64KiB smaller: | % ls -al Image-* | -rw-r--r-- 1 mark mark 37108224 Aug 23 09:56 Image-after | -rw-r--r-- 1 mark mark 37173760 Aug 23 09:54 Image-before According to bloat-o-meter.pl: | add/remove: 44/34 grow/shrink: 602/1294 up/down: 39692/-61108 (-21416) | Function old new delta | [...] | Total: Before=16618336, After=16596920, chg -0.13% | add/remove: 0/2 grow/shrink: 0/0 up/down: 0/-1296 (-1296) | Data old new delta | arm64_const_caps_ready 16 - -16 | cpu_hwcap_keys 1280 - -1280 | Total: Before=8987120, After=8985824, chg -0.01% | add/remove: 0/0 grow/shrink: 0/0 up/down: 0/0 (0) | RO Data old new delta | Total: Before=18408, After=18408, chg +0.00% Signed-off-by: Mark Rutland Cc: Ard Biesheuvel Cc: James Morse Cc: Joey Gouly Cc: Marc Zyngier Cc: Will Deacon Reviewed-by: Ard Biesheuvel Link: https://lore.kernel.org/r/20220912162210.3626215-8-mark.rutland@arm.com Signed-off-by: Catalin Marinas

arm64: atomics: remove redundant static branch

2022-02-15T17:54:08+00:00

Due to a historical oversight, we emit a redundant static branch for each atomic/atomic64 operation when CONFIG_ARM64_LSE_ATOMICS is selected. We can safely remove this, making the kernel Image reasonably smaller. When CONFIG_ARM64_LSE_ATOMICS is selected, every LSE atomic operation has two preceding static branches with the same target, e.g. b f7c b f7c mov w0, #0x1 // #1 ldadd w0, w0, [x19] This is because the __lse_ll_sc_body() wrapper uses system_uses_lse_atomics(), which checks both `arm64_const_caps_ready` and `cpu_hwcap_keys[ARM64_HAS_LSE_ATOMICS]`, each of which emits a static branch. This has been the case since commit: addfc38672c73efd ("arm64: atomics: avoid out-of-line ll/sc atomics") However, there was never a need to check `arm64_const_caps_ready`, which was itself introduced in commit: 63a1e1c95e60e798 ("arm64/cpufeature: don't use mutex in bringup path") ... so that cpus_have_const_cap() could fall back to checking the `cpu_hwcaps` bitmap prior to the static keys for individual caps becoming enabled. As system_uses_lse_atomics() doesn't check `cpu_hwcaps`, and doesn't need to as we can safely use the LL/SC atomics prior to enabling the `ARM64_HAS_LSE_ATOMICS` static key, it doesn't need to check `arm64_const_caps_ready`. This patch removes the `arm64_const_caps_ready` check from system_uses_lse_atomics(). As the arch_atomic_* routines are meant to be safely usable in noinstr code, I've also marked system_uses_lse_atomics() as __always_inline. This results in one fewer static branch per atomic operation, with the prior example becoming: b f78 mov w0, #0x1 // #1 ldadd w0, w0, [x19] Each static branch consists of the branch itself and an associated __jump_table entry. Removing these has a reasonable impact on the Image size, with a GCC 11.1.0 defconfig v5.17-rc2 Image being reduced by 128KiB: | [mark@lakrids:~/src/linux]% ls -al Image* | -rw-r--r-- 1 mark mark 34619904 Feb 3 18:24 Image.baseline | -rw-r--r-- 1 mark mark 34488832 Feb 3 18:33 Image.onebranch Signed-off-by: Mark Rutland Cc: Ard Biesheuvel Cc: Catalin Marinas Cc: Suzuki Poulose Cc: Will Deacon Link: https://lore.kernel.org/r/20220204104439.270567-1-mark.rutland@arm.com Signed-off-by: Will Deacon

arm64: lse: Fix LSE atomics with LLVM

2020-02-18T18:10:49+00:00

Commit e0d5896bd356 ("arm64: lse: fix LSE atomics with LLVM's integrated assembler") broke the build when clang is used in connjunction with the binutils assembler ("-no-integrated-as"). This happens because __LSE_PREAMBLE is defined as ".arch armv8-a+lse", which overrides the version of the CPU architecture passed via the "-march" paramter to gas: $ aarch64-none-linux-gnu-as -EL -I ./arch/arm64/include -I ./arch/arm64/include/generated -I ./include -I ./include -I ./arch/arm64/include/uapi -I ./arch/arm64/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi -I ./init -I ./init -march=armv8.3-a -o init/do_mounts.o /tmp/do_mounts-d7992a.s /tmp/do_mounts-d7992a.s: Assembler messages: /tmp/do_mounts-d7992a.s:1959: Error: selected processor does not support `autiasp' /tmp/do_mounts-d7992a.s:2021: Error: selected processor does not support `paciasp' /tmp/do_mounts-d7992a.s:2157: Error: selected processor does not support `autiasp' /tmp/do_mounts-d7992a.s:2175: Error: selected processor does not support `paciasp' /tmp/do_mounts-d7992a.s:2494: Error: selected processor does not support `autiasp' Fix the issue by replacing ".arch armv8-a+lse" with ".arch_extension lse". Sami confirms that the clang integrated assembler does now support the '.arch_extension' directive, so this change will be fine even for LTO builds in future. Fixes: e0d5896bd356cd ("arm64: lse: fix LSE atomics with LLVM's integrated assembler") Cc: Catalin Marinas Cc: Will Deacon Reported-by: Amit Kachhap Tested-by: Sami Tolvanen Signed-off-by: Vincenzo Frascino Signed-off-by: Will Deacon

Merge branches 'for-next/acpi', 'for-next/cpufeatures', 'for-next/csum', 'for-next/e0pd', 'for-next/entry', 'for-next/kbuild', 'for-next/kexec/cleanup', 'for-next/kexec/file-kdump', 'for-next/misc', 'for-next/nofpsimd', 'for-next/perf' and 'for-next/scs' into for-next/core

2020-01-22T11:32:31+00:00

* for-next/acpi: ACPI/IORT: Fix 'Number of IDs' handling in iort_id_map() * for-next/cpufeatures: (2 commits) arm64: Introduce ID_ISAR6 CPU register ... * for-next/csum: (2 commits) arm64: csum: Fix pathological zero-length calls ... * for-next/e0pd: (7 commits) arm64: kconfig: Fix alignment of E0PD help text ... * for-next/entry: (5 commits) arm64: entry: cleanup sp_el0 manipulation ... * for-next/kbuild: (4 commits) arm64: kbuild: remove compressed images on 'make ARCH=arm64 (dist)clean' ... * for-next/kexec/cleanup: (11 commits) Revert "arm64: kexec: make dtb_mem always enabled" ... * for-next/kexec/file-kdump: (2 commits) arm64: kexec_file: add crash dump support ... * for-next/misc: (12 commits) arm64: entry: Avoid empty alternatives entries ... * for-next/nofpsimd: (7 commits) arm64: nofpsmid: Handle TIF_FOREIGN_FPSTATE flag cleanly ... * for-next/perf: (2 commits) perf/imx_ddr: Fix cpu hotplug state cleanup ... * for-next/scs: (6 commits) arm64: kernel: avoid x18 in __cpu_soft_restart ...

arm64: lse: fix LSE atomics with LLVM's integrated assembler

2020-01-16T17:25:10+00:00

Unlike gcc, clang considers each inline assembly block to be independent and therefore, when using the integrated assembler for inline assembly, any preambles that enable features must be repeated in each block. This change defines __LSE_PREAMBLE and adds it to each inline assembly block that has LSE instructions, which allows them to be compiled also with clang's assembler. Link: https://github.com/ClangBuiltLinux/linux/issues/671 Signed-off-by: Sami Tolvanen Tested-by: Andrew Murray Tested-by: Kees Cook Reviewed-by: Andrew Murray Reviewed-by: Kees Cook Reviewed-by: Nick Desaulniers Signed-off-by: Will Deacon

arm64: Move the LSE gas support detection to Kconfig

2020-01-15T12:50:48+00:00

As the Kconfig syntax gained support for $(as-instr) tests, move the LSE gas support detection from Makefile to the main arm64 Kconfig and remove the additional CONFIG_AS_LSE definition and check. Cc: Will Deacon Reviewed-by: Vladimir Murzin Tested-by: Vladimir Murzin Signed-off-by: Catalin Marinas Signed-off-by: Will Deacon