The vector regset uses the maximum possible vlen value to estimate the
.n field. But not all the hardwares support the maximum vlen. Linux
might wastes time to prepare a large memory buffer(about 2^6 pages) for
the vector regset.

The regset can only copy vector registers when the process are using
vector. Add .active callback and determine the n field of vector regset
in riscv_v_setup_ctx_cache() doesn't affect the ptrace syscall and
coredump. It can avoid oversized allocations and better matches real
hardware limits.

Signed-off-by: Yong-Xuan Wang <yongxuan.wang@sifive.com>
Reviewed-by: Greentime Hu <greentime.hu@sifive.com>
Reviewed-by: Andy Chiu <andybnac@gmail.com>
---
 arch/riscv/include/asm/vector.h |  1 +
 arch/riscv/kernel/ptrace.c      | 24 +++++++++++++++++++++---
 arch/riscv/kernel/vector.c      |  2 ++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
index b61786d43c20..e7aa449368ad 100644
--- a/arch/riscv/include/asm/vector.h
+++ b/arch/riscv/include/asm/vector.h
@@ -51,6 +51,7 @@ void put_cpu_vector_context(void);
 void riscv_v_thread_free(struct task_struct *tsk);
 void __init riscv_v_setup_ctx_cache(void);
 void riscv_v_thread_alloc(struct task_struct *tsk);
+void __init update_regset_vector_info(unsigned long size);
 
 static inline u32 riscv_v_flags(void)
 {
diff --git a/arch/riscv/kernel/ptrace.c b/arch/riscv/kernel/ptrace.c
index 8e86305831ea..e6272d74572f 100644
--- a/arch/riscv/kernel/ptrace.c
+++ b/arch/riscv/kernel/ptrace.c
@@ -153,6 +153,17 @@ static int riscv_vr_set(struct task_struct *target,
 				 0, riscv_v_vsize);
 	return ret;
 }
+
+static int riscv_vr_active(struct task_struct *target, const struct user_regset *regset)
+{
+	if (!(has_vector() || has_xtheadvector()))
+		return -ENODEV;
+
+	if (!riscv_v_vstate_query(task_pt_regs(target)))
+		return 0;
+
+	return regset->n;
+}
 #endif
 
 #ifdef CONFIG_RISCV_ISA_SUPM
@@ -184,7 +195,7 @@ static int tagged_addr_ctrl_set(struct task_struct *target,
 }
 #endif
 
-static const struct user_regset riscv_user_regset[] = {
+static struct user_regset riscv_user_regset[] __ro_after_init = {
 	[REGSET_X] = {
 		USER_REGSET_NOTE_TYPE(PRSTATUS),
 		.n = ELF_NGREG,
@@ -207,11 +218,10 @@ static const struct user_regset riscv_user_regset[] = {
 	[REGSET_V] = {
 		USER_REGSET_NOTE_TYPE(RISCV_VECTOR),
 		.align = 16,
-		.n = ((32 * RISCV_MAX_VLENB) +
-		      sizeof(struct __riscv_v_regset_state)) / sizeof(__u32),
 		.size = sizeof(__u32),
 		.regset_get = riscv_vr_get,
 		.set = riscv_vr_set,
+		.active = riscv_vr_active,
 	},
 #endif
 #ifdef CONFIG_RISCV_ISA_SUPM
@@ -233,6 +243,14 @@ static const struct user_regset_view riscv_user_native_view = {
 	.n = ARRAY_SIZE(riscv_user_regset),
 };
 
+#ifdef CONFIG_RISCV_ISA_V
+void __init update_regset_vector_info(unsigned long size)
+{
+	riscv_user_regset[REGSET_V].n = (size + sizeof(struct __riscv_v_regset_state)) /
+					sizeof(__u32);
+}
+#endif
+
 struct pt_regs_offset {
 	const char *name;
 	int offset;
diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 901e67adf576..3ed071dab9d8 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -66,6 +66,8 @@ void __init riscv_v_setup_ctx_cache(void)
 	if (!(has_vector() || has_xtheadvector()))
 		return;
 
+	update_regset_vector_info(riscv_v_vsize);
+
 	riscv_v_user_cachep = kmem_cache_create_usercopy("riscv_vector_ctx",
 							 riscv_v_vsize, 16, SLAB_PANIC,
 							 0, riscv_v_vsize, NULL);
-- 
2.43.0