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>

arch/s390/include/asm/timex.h

@@ -49,6 +49,13 @@ static inline void set_clock_comparator(__u64 time)
 	asm volatile("sckc %0" : : "Q" (time));
 }
 
+static inline void set_tod_programmable_field(u16 val)
+{
+	register unsigned long reg0 asm("0") = val;
+
+	asm volatile("sckpf" : : "d" (reg0));
+}
+
 void clock_comparator_work(void);
 
 void __init time_early_init(void);

arch/s390/include/asm/vdso.h

@@ -14,5 +14,7 @@
 
 extern struct vdso_data *vdso_data;
 
+void vdso_getcpu_init(void);
+
 #endif /* __ASSEMBLY__ */
 #endif /* __S390_VDSO_H__ */

arch/s390/kernel/smp.c

@@ -54,6 +54,7 @@
 #include <asm/nmi.h>
 #include <asm/stacktrace.h>
 #include <asm/topology.h>
+#include <asm/vdso.h>
 #include "entry.h"
 
 enum {
@@ -858,6 +859,7 @@ static void smp_init_secondary(void)
 	preempt_disable();
 	init_cpu_timer();
 	vtime_init();
+	vdso_getcpu_init();
 	pfault_init();
 	notify_cpu_starting(cpu);
 	if (topology_cpu_dedicated(cpu))

arch/s390/kernel/vdso.c

@@ -29,6 +29,7 @@
 #include <asm/sections.h>
 #include <asm/vdso.h>
 #include <asm/facility.h>
+#include <asm/timex.h>
 
 extern char vdso64_start, vdso64_end;
 static void *vdso64_kbase = &vdso64_start;
@@ -100,6 +101,11 @@ static union {
 } vdso_data_store __page_aligned_data;
 struct vdso_data *vdso_data = (struct vdso_data *)&vdso_data_store.data;
 
+void vdso_getcpu_init(void)
+{
+	set_tod_programmable_field(smp_processor_id());
+}
+
 /*
  * This is called from binfmt_elf, we create the special vma for the
  * vDSO and insert it into the mm struct tree
@@ -170,6 +176,7 @@ static int __init vdso_init(void)
 {
 	int i;
 
+	vdso_getcpu_init();
 	/* Calculate the size of the 64 bit vDSO */
 	vdso64_pages = ((&vdso64_end - &vdso64_start
 			 + PAGE_SIZE - 1) >> PAGE_SHIFT) + 1;

arch/s390/kernel/vdso64/Makefile

@@ -7,7 +7,8 @@ ARCH_REL_TYPE_ABS += R_390_GOT|R_390_PLT
 
 include $(srctree)/lib/vdso/Makefile
 obj-vdso64 = vdso_user_wrapper.o note.o
-obj-cvdso64 = vdso64_generic.o
+obj-cvdso64 = vdso64_generic.o getcpu.o
+CFLAGS_REMOVE_getcpu.o = -pg $(CC_FLAGS_FTRACE) $(CC_FLAGS_EXPOLINE)
 CFLAGS_REMOVE_vdso64_generic.o = -pg $(CC_FLAGS_FTRACE) $(CC_FLAGS_EXPOLINE)
 
 # Build rules

arch/s390/kernel/vdso64/getcpu.c

+// 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;
+}

arch/s390/kernel/vdso64/vdso64.lds.S

@@ -135,7 +135,7 @@ VERSION
 		__kernel_gettimeofday;
 		__kernel_clock_gettime;
 		__kernel_clock_getres;
-
+		__kernel_getcpu;
 	local: *;
 	};
 }

arch/s390/kernel/vdso64/vdso_user_wrapper.S

@@ -36,3 +36,4 @@ __kernel_\func:
 vdso_func gettimeofday
 vdso_func clock_getres
 vdso_func clock_gettime
+vdso_func getcpu