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The hwprobe vDSO data for some keys, like MISALIGNED_VECTOR_PERF, is determined by an asynchronous kthread. This can create a race condition where the kthread finishes after the vDSO data has already been populated, causing userspace to read stale values. To fix this race, a new 'ready' flag is added to the vDSO data, initialized to 'false' during arch_initcall_sync. This flag is checked by both the vDSO's user-space code and the riscv_hwprobe syscall. The syscall serves as a one-time gate, using a completion to wait for any pending probes before populating the data and setting the flag to 'true', thus ensuring userspace reads fresh values on its first request. Reported-by: Tsukasa OI <research_trasio@irq.a4lg.com> Closes: https://lore.kernel.org/linux-riscv/760d637b-b13b-4518-b6bf-883d55d44e7f@irq.a4lg.com/ Fixes: e7c9d66e313b ("RISC-V: Report vector unaligned access speed hwprobe") Cc: Palmer Dabbelt <palmer@dabbelt.com> Cc: Alexandre Ghiti <alexghiti@rivosinc.com> Cc: Olof Johansson <olof@lixom.net> Cc: stable@vger.kernel.org Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com> Co-developed-by: Palmer Dabbelt <palmer@dabbelt.com> Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com> Signed-off-by: Jingwei Wang <wangjingwei@iscas.ac.cn> Link: https://lore.kernel.org/r/20250811142035.105820-1-wangjingwei@iscas.ac.cn [pjw@kernel.org: fix checkpatch issues] Signed-off-by: Paul Walmsley <pjw@kernel.org>
24 lines
638 B
C
24 lines
638 B
C
/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef __RISCV_ASM_VDSO_ARCH_DATA_H
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#define __RISCV_ASM_VDSO_ARCH_DATA_H
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#include <linux/types.h>
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#include <vdso/datapage.h>
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#include <asm/hwprobe.h>
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struct vdso_arch_data {
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/* Stash static answers to the hwprobe queries when all CPUs are selected. */
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__u64 all_cpu_hwprobe_values[RISCV_HWPROBE_MAX_KEY + 1];
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/* Boolean indicating all CPUs have the same static hwprobe values. */
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__u8 homogeneous_cpus;
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/*
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* A gate to check and see if the hwprobe data is actually ready, as
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* probing is deferred to avoid boot slowdowns.
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*/
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__u8 ready;
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};
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#endif /* __RISCV_ASM_VDSO_ARCH_DATA_H */
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