s390/vdso: reimplement getcpu vdso syscall

Implement the previously removed getcpu vdso syscall by using the
TOD programmable field to pass the cpu number to user space.

Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/s390/kernel/vdso64/getcpu.c b/arch/s390/kernel/vdso64/getcpu.c
new file mode 100644
index 000000000000..a5da7a9eb43d
--- /dev/null
+++ b/arch/s390/kernel/vdso64/getcpu.c
@@ -0,0 +1,20 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright IBM Corp. 2020 */
+
+#include <linux/compiler.h>
+#include <linux/getcpu.h>
+#include <asm/timex.h>
+
+int __s390_vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
+{
+	__u16 todval[8];
+
+	/* CPU number is stored in the programmable field of the TOD clock */
+	get_tod_clock_ext((char *)todval);
+	if (cpu)
+		*cpu = todval[7];
+	/* NUMA node is always zero */
+	if (node)
+		*node = 0;
+	return 0;
+}