[PATCH] riscv: hwprobe: Fix stale vDSO data for late-initialized keys at boot

* [PATCH] riscv: hwprobe: Fix stale vDSO data for late-initialized keys at boot
@ 2025-05-21  5:27 wangjingwei
  2025-05-21  7:52 ` Yixun Lan
  0 siblings, 1 reply; 3+ messages in thread
From: wangjingwei @ 2025-05-21  5:27 UTC (permalink / raw)
  To: linux-riscv
  Cc: Paul Walmsley, Palmer Dabbelt, Albert Ou, Alexandre Ghiti,
	Andrew Jones, Conor Dooley, Clément Léger,
	Charlie Jenkins, Tsukasa OI, Jingwei Wang

From: Jingwei Wang <wangjingwei@iscas.ac.cn>

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.

This patch introduces riscv_hwprobe_vdso_sync(sync_key). This function
is now called by the vec_check_unaligned_access_speed_all_cpus kthread
upon its completion. It re-evaluates the specified key using current kernel
state (including the finalized per-CPU data) via hwprobe_one_pair()
and updates the corresponding entry in vdso_k_arch_data.

This ensures the vDSO accurately reflects the final boot-time values
for keys determined by such asynchronous boot tasks, resolving observed
inconsistencies when userspace starts.

Test by comparing vDSO and syscall results for affected keys
(e.g., MISALIGNED_VECTOR_PERF), which now match their final
boot-time values.

Reported-by: Tsukasa OI <research_trasio@irq.a4lg.com>
Closes: https://lore.kernel.org/linux-riscv/760d637b-b13b-4518-b6bf-883d55d44e7f@irq.a4lg.com/
Signed-off-by: Jingwei Wang <wangjingwei@iscas.ac.cn>
---
 arch/riscv/include/asm/hwprobe.h           |  4 ++++
 arch/riscv/kernel/sys_hwprobe.c            | 16 ++++++++++++++++
 arch/riscv/kernel/unaligned_access_speed.c |  4 +++-
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
index 1f690fea0e03de6a..02c34f03d8b9bc83 100644
--- a/arch/riscv/include/asm/hwprobe.h
+++ b/arch/riscv/include/asm/hwprobe.h
@@ -40,4 +40,8 @@ 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);
+#endif /* CONFIG_MMU */
+
 #endif
diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index 249aec8594a92a80..c2593bd766055d35 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..7194aee3bf3234e5 100644
--- a/arch/riscv/kernel/unaligned_access_speed.c
+++ b/arch/riscv/kernel/unaligned_access_speed.c
@@ -375,7 +375,9 @@ 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);
-
+#ifdef CONFIG_MMU
+	riscv_hwprobe_vdso_sync(RISCV_HWPROBE_KEY_MISALIGNED_VECTOR_PERF);
+#endif
 	return 0;
 }
 #else /* CONFIG_RISCV_PROBE_VECTOR_UNALIGNED_ACCESS */
-- 
2.49.0


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