kernel/linux.git/arch/arm64/include/asm/simd.h, branch v6.19.12

arm64/simd: Avoid pointless clearing of FP/SIMD buffer

2025-12-14T18:18:22+00:00

The buffer provided to kernel_neon_begin() is only used if the task is scheduled out while the FP/SIMD is in use by the kernel, or when such a section is interrupted by a softirq that also uses the FP/SIMD. IOW, this happens rarely, and even if it happened often, there is still no reason for this buffer to be cleared beforehand, which happens unconditionally, due to the use of a compound literal expression. So define that buffer variable explicitly, and mark it as __uninitialized so that it will not get cleared, even when -ftrivial-auto-var-init is in effect. This requires some preprocessor gymnastics, due to the fact that the variable must be defined throughout the entire guarded scope, and the expression ({ struct user_fpsimd_state __uninitialized st; &st; }) is problematic in that regard, even though the compilers seem to permit it. So instead, repeat the 'for ()' trick that is also used in the implementation of the guarded scope helpers. Cc: Will Deacon Cc: Catalin Marinas Cc: Kees Cook Cc: Eric Biggers Signed-off-by: Ard Biesheuvel Fixes: 4fa617cc6851 ("arm64/fpsimd: Allocate kernel mode FP/SIMD buffers on the stack") Link: https://lore.kernel.org/r/20251209054848.998878-2-ardb@kernel.org Signed-off-by: Eric Biggers

Merge tag 'fpsimd-on-stack-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux

2025-12-03T02:53:50+00:00

Pull arm64 FPSIMD on-stack buffer updates from Eric Biggers: "This is a core arm64 change. However, I was asked to take this because most uses of kernel-mode FPSIMD are in crypto or CRC code. In v6.8, the size of task_struct on arm64 increased by 528 bytes due to the new 'kernel_fpsimd_state' field. This field was added to allow kernel-mode FPSIMD code to be preempted. Unfortunately, 528 bytes is kind of a lot for task_struct. This regression in the task_struct size was noticed and reported. Recover that space by making this state be allocated on the stack at the beginning of each kernel-mode FPSIMD section. To make it easier for all the users of kernel-mode FPSIMD to do that correctly, introduce and use a 'scoped_ksimd' abstraction" * tag 'fpsimd-on-stack-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/ebiggers/linux: (23 commits) lib/crypto: arm64: Move remaining algorithms to scoped ksimd API lib/crypto: arm/blake2b: Move to scoped ksimd API arm64/fpsimd: Allocate kernel mode FP/SIMD buffers on the stack arm64/fpu: Enforce task-context only for generic kernel mode FPU net/mlx5: Switch to more abstract scoped ksimd guard API on arm64 arm64/xorblocks: Switch to 'ksimd' scoped guard API crypto/arm64: sm4 - Switch to 'ksimd' scoped guard API crypto/arm64: sm3 - Switch to 'ksimd' scoped guard API crypto/arm64: sha3 - Switch to 'ksimd' scoped guard API crypto/arm64: polyval - Switch to 'ksimd' scoped guard API crypto/arm64: nhpoly1305 - Switch to 'ksimd' scoped guard API crypto/arm64: aes-gcm - Switch to 'ksimd' scoped guard API crypto/arm64: aes-blk - Switch to 'ksimd' scoped guard API crypto/arm64: aes-ccm - Switch to 'ksimd' scoped guard API raid6: Move to more abstract 'ksimd' guard API crypto: aegis128-neon - Move to more abstract 'ksimd' guard API crypto/arm64: sm4-ce-gcm - Avoid pointless yield of the NEON unit crypto/arm64: sm4-ce-ccm - Avoid pointless yield of the NEON unit crypto/arm64: aes-ce-ccm - Avoid pointless yield of the NEON unit lib/crc: Switch ARM and arm64 to 'ksimd' scoped guard API ...

arm64/fpsimd: Allocate kernel mode FP/SIMD buffers on the stack

2025-11-12T08:52:03+00:00

Commit aefbab8e77eb16b5 ("arm64: fpsimd: Preserve/restore kernel mode NEON at context switch") added a 'kernel_fpsimd_state' field to struct thread_struct, which is the arch-specific portion of struct task_struct, and is allocated for each task in the system. The size of this field is 528 bytes, resulting in non-negligible bloat of task_struct, and the resulting memory overhead may impact performance on systems with many processes. This allocation is only used if the task is scheduled out or interrupted by a softirq while using the FP/SIMD unit in kernel mode, and so it is possible to transparently allocate this buffer on the caller's stack instead. So tweak the 'ksimd' scoped guard implementation so that a stack buffer is allocated and passed to both kernel_neon_begin() and kernel_neon_end(), and either record it in the task struct, or use it directly to preserve the task mode kernel FP/SIMD when running in softirq context. Passing the address to both functions, and checking the addresses for consistency ensures that callers of the updated bare begin/end API use it in a manner that is consistent with the new context switch semantics. Acked-by: Catalin Marinas Signed-off-by: Ard Biesheuvel

arm64/simd: Add scoped guard API for kernel mode SIMD

2025-11-12T08:22:39+00:00

Encapsulate kernel_neon_begin() and kernel_neon_end() using a 'ksimd' cleanup guard. This hides the prototype of those functions, allowing them to be changed for arm64 but not ARM, without breaking code that is shared between those architectures (RAID6, AEGIS-128) It probably makes sense to expose this API more widely across architectures, as it affords more flexibility to the arch code to plumb it in, while imposing more rigid rules regarding the start/end bookends appearing in matched pairs. Reviewed-by: Kees Cook Reviewed-by: Mark Brown Reviewed-by: Eric Biggers Reviewed-by: Jonathan Cameron Acked-by: Catalin Marinas Signed-off-by: Ard Biesheuvel

arm64/fpsimd: Permit kernel mode NEON with IRQs off

2025-11-11T18:59:22+00:00

Currently, may_use_simd() will return false when called from a context where IRQs are disabled. One notable case where this happens is when calling the ResetSystem() EFI runtime service from the reboot/poweroff code path. For this case alone, there is a substantial amount of FP/SIMD support code to handle the corner case where a EFI runtime service is invoked with IRQs disabled. The only reason kernel mode SIMD is not allowed when IRQs are disabled is that re-enabling softirqs in this case produces a noisy diagnostic when lockdep is enabled. The warning is valid, in the sense that delivering pending softirqs over the back of the call to local_bh_enable() is problematic when IRQs are disabled. While the API lacks a facility to simply mask and unmask softirqs without triggering their delivery, disabling softirqs is not needed to begin with when IRQs are disabled, given that softirqs are only every taken asynchronously over the back of a hard IRQ. So dis/enable softirq processing conditionally, based on whether IRQs are enabled, and relax the check in may_use_simd(). Acked-by: Will Deacon Signed-off-by: Ard Biesheuvel Acked-by: Catalin Marinas Signed-off-by: Catalin Marinas

arm64: fpsimd: Drop unneeded 'busy' flag

2023-12-12T14:29:16+00:00

Kernel mode NEON will preserve the user mode FPSIMD state by saving it into the task struct before clobbering the registers. In order to avoid the need for preserving kernel mode state too, we disallow nested use of kernel mode NEON, i..e, use in softirq context while the interrupted task context was using kernel mode NEON too. Originally, this policy was implemented using a per-CPU flag which was exposed via may_use_simd(), requiring the users of the kernel mode NEON to deal with the possibility that it might return false, and having NEON and non-NEON code paths. This policy was changed by commit 13150149aa6ded1 ("arm64: fpsimd: run kernel mode NEON with softirqs disabled"), and now, softirq processing is disabled entirely instead, and so may_use_simd() can never fail when called from task or softirq context. This means we can drop the fpsimd_context_busy flag entirely, and instead, ensure that we disable softirq processing in places where we formerly relied on the flag for preventing races in the FPSIMD preserve routines. Signed-off-by: Ard Biesheuvel Reviewed-by: Mark Brown Tested-by: Geert Uytterhoeven Link: https://lore.kernel.org/r/20231208113218.3001940-7-ardb@google.com [will: Folded in fix from CAMj1kXFhzbJRyWHELCivQW1yJaF=p07LLtbuyXYX3G1WtsdyQg@mail.gmail.com] Signed-off-by: Will Deacon

arm64: replace in_irq() with in_hardirq()

2021-08-20T18:49:38+00:00

Replace the obsolete and ambiguos macro in_irq() with new macro in_hardirq(). Signed-off-by: Changbin Du Link: https://lore.kernel.org/r/20210814005405.2658-1-changbin.du@gmail.com Signed-off-by: Catalin Marinas

arm64: fpsimd: Make sure SVE setup is complete before SIMD is used

2020-01-14T17:11:21+00:00

In-kernel users of NEON rely on may_use_simd() to check if the SIMD can be used. However, we must initialize the SVE before SIMD can be used. Add a sanity check to make sure that we have completed the SVE setup before anyone uses the SIMD. Cc: Ard Biesheuvel Cc: Mark Rutland Cc: Will Deacon Reviewed-by: Ard Biesheuvel Reviewed-by: Catalin Marinas Signed-off-by: Suzuki K Poulose Signed-off-by: Will Deacon

Merge tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux

2019-07-08T16:54:55+00:00

Pull arm64 updates from Catalin Marinas: - arm64 support for syscall emulation via PTRACE_SYSEMU{,_SINGLESTEP} - Wire up VM_FLUSH_RESET_PERMS for arm64, allowing the core code to manage the permissions of executable vmalloc regions more strictly - Slight performance improvement by keeping softirqs enabled while touching the FPSIMD/SVE state (kernel_neon_begin/end) - Expose a couple of ARMv8.5 features to user (HWCAP): CondM (new XAFLAG and AXFLAG instructions for floating point comparison flags manipulation) and FRINT (rounding floating point numbers to integers) - Re-instate ARM64_PSEUDO_NMI support which was previously marked as BROKEN due to some bugs (now fixed) - Improve parking of stopped CPUs and implement an arm64-specific panic_smp_self_stop() to avoid warning on not being able to stop secondary CPUs during panic - perf: enable the ARM Statistical Profiling Extensions (SPE) on ACPI platforms - perf: DDR performance monitor support for iMX8QXP - cache_line_size() can now be set from DT or ACPI/PPTT if provided to cope with a system cache info not exposed via the CPUID registers - Avoid warning on hardware cache line size greater than ARCH_DMA_MINALIGN if the system is fully coherent - arm64 do_page_fault() and hugetlb cleanups - Refactor set_pte_at() to avoid redundant READ_ONCE(*ptep) - Ignore ACPI 5.1 FADTs reported as 5.0 (infer from the 'arm_boot_flags' introduced in 5.1) - CONFIG_RANDOMIZE_BASE now enabled in defconfig - Allow the selection of ARM64_MODULE_PLTS, currently only done via RANDOMIZE_BASE (and an erratum workaround), allowing modules to spill over into the vmalloc area - Make ZONE_DMA32 configurable * tag 'arm64-upstream' of git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux: (54 commits) perf: arm_spe: Enable ACPI/Platform automatic module loading arm_pmu: acpi: spe: Add initial MADT/SPE probing ACPI/PPTT: Add function to return ACPI 6.3 Identical tokens ACPI/PPTT: Modify node flag detection to find last IDENTICAL x86/entry: Simplify _TIF_SYSCALL_EMU handling arm64: rename dump_instr as dump_kernel_instr arm64/mm: Drop [PTE|PMD]_TYPE_FAULT arm64: Implement panic_smp_self_stop() arm64: Improve parking of stopped CPUs arm64: Expose FRINT capabilities to userspace arm64: Expose ARMv8.5 CondM capability to userspace arm64: defconfig: enable CONFIG_RANDOMIZE_BASE arm64: ARM64_MODULES_PLTS must depend on MODULES arm64: bpf: do not allocate executable memory arm64/kprobes: set VM_FLUSH_RESET_PERMS on kprobe instruction pages arm64/mm: wire up CONFIG_ARCH_HAS_SET_DIRECT_MAP arm64: module: create module allocations without exec permissions arm64: Allow user selection of ARM64_MODULE_PLTS acpi/arm64: ignore 5.1 FADTs that are reported as 5.0 arm64: Allow selecting Pseudo-NMI again ...

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 500

2019-06-19T15:09:55+00:00

Based on 2 normalized pattern(s): this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation this program is free software you can redistribute it and or modify it under the terms of the gnu general public license version 2 as published by the free software foundation # extracted by the scancode license scanner the SPDX license identifier GPL-2.0-only has been chosen to replace the boilerplate/reference in 4122 file(s). Signed-off-by: Thomas Gleixner Reviewed-by: Enrico Weigelt Reviewed-by: Kate Stewart Reviewed-by: Allison Randal Cc: linux-spdx@vger.kernel.org Link: https://lkml.kernel.org/r/20190604081206.933168790@linutronix.de Signed-off-by: Greg Kroah-Hartman