diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
index 184f780c932d44..6ba68568735bbc 100644
--- a/arch/riscv/kernel/vector.c
+++ b/arch/riscv/kernel/vector.c
@@ -120,6 +120,8 @@ static int riscv_v_thread_zalloc(struct kmem_cache *cache,
 
 	ctx->datap = datap;
 	memset(ctx, 0, offsetof(struct __riscv_v_ext_state, datap));
+	ctx->vlenb = riscv_v_vsize / 32;
+
 	return 0;
 }
 
diff --git a/tools/testing/selftests/riscv/vector/.gitignore b/tools/testing/selftests/riscv/vector/.gitignore
index 7d9c87cd064979..d21c03c3ee0e2b 100644
--- a/tools/testing/selftests/riscv/vector/.gitignore
+++ b/tools/testing/selftests/riscv/vector/.gitignore
@@ -2,3 +2,4 @@ vstate_exec_nolibc
 vstate_prctl
 v_initval
 v_exec_initval_nolibc
+v_ptrace
diff --git a/tools/testing/selftests/riscv/vector/Makefile b/tools/testing/selftests/riscv/vector/Makefile
index 6f7497f4e7b30d..c14ad127e7fb52 100644
--- a/tools/testing/selftests/riscv/vector/Makefile
+++ b/tools/testing/selftests/riscv/vector/Makefile
@@ -2,7 +2,7 @@
 # Copyright (C) 2021 ARM Limited
 # Originally tools/testing/arm64/abi/Makefile
 
-TEST_GEN_PROGS := v_initval vstate_prctl
+TEST_GEN_PROGS := v_initval vstate_prctl v_ptrace
 TEST_GEN_PROGS_EXTENDED := vstate_exec_nolibc v_exec_initval_nolibc
 
 include ../../lib.mk
@@ -26,3 +26,6 @@ $(OUTPUT)/v_initval: v_initval.c $(OUTPUT)/sys_hwprobe.o $(OUTPUT)/v_helpers.o
 $(OUTPUT)/v_exec_initval_nolibc: v_exec_initval_nolibc.c
 	$(CC) -nostdlib -static -include ../../../../include/nolibc/nolibc.h \
 		-Wall $(CFLAGS) $(LDFLAGS) $^ -o $@ -lgcc
+
+$(OUTPUT)/v_ptrace: v_ptrace.c $(OUTPUT)/sys_hwprobe.o $(OUTPUT)/v_helpers.o
+	$(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
diff --git a/tools/testing/selftests/riscv/vector/v_ptrace.c b/tools/testing/selftests/riscv/vector/v_ptrace.c
new file mode 100644
index 00000000000000..1ae1b6d443631d
--- /dev/null
+++ b/tools/testing/selftests/riscv/vector/v_ptrace.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <sys/ptrace.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <sys/wait.h>
+#include <sys/uio.h>
+#include <unistd.h>
+#include <errno.h>
+
+#include <linux/ptrace.h>
+#include <linux/elf.h>
+
+#include "../../kselftest_harness.h"
+#include "v_helpers.h"
+
+volatile unsigned long data = 0;
+volatile unsigned long lock = 0;
+
+TEST(ptrace_vlenb)
+{
+	pid_t pid;
+
+	if (!is_vector_supported() && !is_xtheadvector_supported())
+		SKIP(return, "Vector not supported");
+
+	pid = fork();
+
+	ASSERT_LE(0, pid) {
+		TH_LOG("fork: %m");
+	}
+
+	if (pid == 0) {
+		while (lock == 0)
+			asm volatile("" : : "g"(lock) : "memory");
+
+		asm volatile("csrr %[data], vlenb" : [data] "=r"(data));
+		asm volatile ("ebreak" : : : );
+	} else {
+		struct __riscv_v_regset_state *regset_data;
+		size_t regset_size;
+		struct iovec iov;
+		unsigned long vlenb_csr;
+		int status;
+
+		/* attach */
+
+		ASSERT_EQ(0, ptrace(PTRACE_ATTACH, pid, NULL, NULL));
+		ASSERT_EQ(pid, waitpid(pid, &status, 0));
+		ASSERT_TRUE(WIFSTOPPED(status));
+
+		/* unlock */
+
+		ASSERT_EQ(0, ptrace(PTRACE_POKEDATA, pid, &lock, 1));
+
+		/* resume and wait ebreak */
+
+		ASSERT_EQ(0, ptrace(PTRACE_CONT, pid, NULL, NULL));
+		ASSERT_EQ(pid, waitpid(pid, &status, 0));
+		ASSERT_TRUE(WIFSTOPPED(status));
+
+		/* read tracee vlenb via ptrace peek */
+
+		errno = 0;
+		vlenb_csr = ptrace(PTRACE_PEEKDATA, pid, &data, NULL);
+		ASSERT_FALSE((errno != 0) && (vlenb_csr == -1));
+
+		/* read tracee vlenb via ptrace regs */
+
+		regset_size = sizeof(struct __riscv_v_regset_state) +
+			vlenb_csr * 8 * 32;
+		regset_data = calloc(1, regset_size);
+
+		iov.iov_base = regset_data;
+		iov.iov_len = regset_size;
+
+		ASSERT_EQ(0, ptrace(PTRACE_GETREGSET, pid, NT_RISCV_VECTOR, &iov));
+
+		/* compare */
+
+		EXPECT_EQ(vlenb_csr, regset_data->vlenb);
+	}
+}
+
+TEST_HARNESS_MAIN