On Wed, 28 May 2025 07:28:19 PDT (-0700), wangjingwei@iscas.ac.cn wrote:
The riscv_hwprobe vDSO data is populated by init_hwprobe_vdso_data(), an arch_initcall_sync. However, underlying data for some keys, like RISCV_HWPROBE_KEY_MISALIGNED_VECTOR_PERF, is determined asynchronously.
Specifically, the per_cpu(vector_misaligned_access, cpu) values are set by the vec_check_unaligned_access_speed_all_cpus kthread. This kthread is spawned by an earlier arch_initcall (check_unaligned_access_all_cpus) and may complete its benchmark *after* init_hwprobe_vdso_data() has already populated the vDSO with default/stale values.
IIUC there's another race here: we don't ensure these complete before allowing userspace to see the values, so if these took so long to probe userspace started to make hwprobe() calls before they got scheduled we'd be providing the wrong answer.
Unless I'm just missing something, though -- I thought we'd looked at that case?
So, refresh the vDSO data for specified keys (e.g., MISALIGNED_VECTOR_PERF) ensuring it reflects the final boot-time values.
Test by comparing vDSO and syscall results for affected keys (e.g., MISALIGNED_VECTOR_PERF), which now match their final boot-time values.
Wouldn't all the other keys we probe via workqueue be racy as well?
Reported-by: Tsukasa OI research_trasio@irq.a4lg.com Closes: https://lore.kernel.org/linux-riscv/760d637b-b13b-4518-b6bf-883d55d44e7f@irq... Fixes: e7c9d66e313b ("RISC-V: Report vector unaligned access speed hwprobe") Cc: stable@vger.kernel.org Reviewed-by: Yanteng Si si.yanteng@linux.dev Reviewed-by: Jesse Taube jesse@rivosinc.com Signed-off-by: Jingwei Wang wangjingwei@iscas.ac.cn
Changes in v3:
- Retained existing blank line.
Changes in v2:
- Addressed feedback from Yixun's regarding #ifdef CONFIG_MMU usage.
- Updated commit message to provide a high-level summary.
- Added Fixes tag for commit e7c9d66e313b.
v1: https://lore.kernel.org/linux-riscv/20250521052754.185231-1-wangjingwei@isca...
arch/riscv/include/asm/hwprobe.h | 6 ++++++ arch/riscv/kernel/sys_hwprobe.c | 16 ++++++++++++++++ arch/riscv/kernel/unaligned_access_speed.c | 1 + 3 files changed, 23 insertions(+)
diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h index 1f690fea0e03de6a..58dc847d86c7f2b0 100644 --- a/arch/riscv/include/asm/hwprobe.h +++ b/arch/riscv/include/asm/hwprobe.h @@ -40,4 +40,10 @@ static inline bool riscv_hwprobe_pair_cmp(struct riscv_hwprobe *pair, return pair->value == other_pair->value; }
+#ifdef CONFIG_MMU +void riscv_hwprobe_vdso_sync(__s64 sync_key); +#else +static inline void riscv_hwprobe_vdso_sync(__s64 sync_key) { }; +#endif /* CONFIG_MMU */
#endif diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c index 249aec8594a92a80..2e3e612b7ac6fd57 100644 --- a/arch/riscv/kernel/sys_hwprobe.c +++ b/arch/riscv/kernel/sys_hwprobe.c @@ -17,6 +17,7 @@ #include <asm/vector.h> #include <asm/vendor_extensions/thead_hwprobe.h> #include <vdso/vsyscall.h> +#include <vdso/datapage.h>
static void hwprobe_arch_id(struct riscv_hwprobe *pair, @@ -500,6 +501,21 @@ static int __init init_hwprobe_vdso_data(void)
arch_initcall_sync(init_hwprobe_vdso_data);
+void riscv_hwprobe_vdso_sync(__s64 sync_key) +{
- struct vdso_arch_data *avd = vdso_k_arch_data;
- struct riscv_hwprobe pair;
- pair.key = sync_key;
- hwprobe_one_pair(&pair, cpu_online_mask);
- /*
* Update vDSO data for the given key.* Currently for non-ID key updates (e.g. MISALIGNED_VECTOR_PERF),* so 'homogeneous_cpus' is not re-evaluated here.*/- avd->all_cpu_hwprobe_values[sync_key] = pair.value;
+}
#endif /* CONFIG_MMU */
SYSCALL_DEFINE5(riscv_hwprobe, struct riscv_hwprobe __user *, pairs, diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c index 585d2dcf2dab1ccb..a2cdb396ff823720 100644 --- a/arch/riscv/kernel/unaligned_access_speed.c +++ b/arch/riscv/kernel/unaligned_access_speed.c @@ -375,6 +375,7 @@ static void check_vector_unaligned_access(struct work_struct *work __always_unus static int __init vec_check_unaligned_access_speed_all_cpus(void *unused __always_unused) { schedule_on_each_cpu(check_vector_unaligned_access);
riscv_hwprobe_vdso_sync(RISCV_HWPROBE_KEY_MISALIGNED_VECTOR_PERF);
return 0;
}