[PATCH v2 8/9] s390/percpu: Provide arch_this_cpu_write() implementation

Heiko Carstens
2026-03-19T12:05:16Z

Provide an s390 specific implementation of arch_this_cpu_write()
instead of the generic variant. The generic variant uses a quite
expensive raw_local_irq_save() / raw_local_irq_restore() pair.

Get rid of this by providing an own variant which makes use of the new
percpu code section infrastructure.

With this the text size of the kernel image is reduced by ~1k (defconfig).

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
---
arch/s390/include/asm/percpu.h | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)

diff --git a/arch/s390/include/asm/percpu.h b/arch/s390/include/asm/percpu.h
index 08c48fa97381..44501a407e6d 100644
--- a/arch/s390/include/asm/percpu.h
+++ b/arch/s390/include/asm/percpu.h
@@ -271,6 +271,38 @@
#define this_cpu_read_4(pcp) arch_this_cpu_read(pcp, "l")
#define this_cpu_read_8(pcp) arch_this_cpu_read(pcp, "lg")

+#define arch_this_cpu_write(pcp, val, op) \
+{ \
+ unsigned long lc_pcpr, lc_pcpo; \
+ typedef typeof(pcp) pcp_op_T__; \
+ pcp_op_T__ val__ = (val); \
+ pcp_op_T__ old__, *ptr__; \
+ \
+ lc_pcpr = offsetof(struct lowcore, percpu_register); \
+ lc_pcpo = offsetof(struct lowcore, percpu_offset); \
+ ptr__ = PERCPU_PTR(&(pcp)); \
+ asm_inline volatile( \
+ MVIY_PERCPU("%[disppcpr]", "%[dispaltpcpr]", "%[ptr__]")\
+ AG_ALT("%[disppcpo]", "%[dispaltpcpo]", "%[ptr__]") \
+ op " %[val__],0(%[ptr__])\n" \
+ MVIY_ALT("%[disppcpr]", "%[dispaltpcpr]", "%%r0") \
+ : [old__] "=&d" (old__), \
+ [ptr__] "+&a" (ptr__), "=m" (*ptr__), \
+ "=m" (((struct lowcore *)0)->percpu_register) \
+ : [val__] "d" (val__), \
+ [disppcpr] "i" (lc_pcpr), \
+ [disppcpo] "i" (lc_pcpo), \
+ [dispaltpcpr] "i" (lc_pcpr + LOWCORE_ALT_ADDRESS), \
+ [dispaltpcpo] "i" (lc_pcpo + LOWCORE_ALT_ADDRESS), \
+ "m" (((struct lowcore *)0)->percpu_offset) \
+ : "cc"); \
+}
+
+#define this_cpu_write_1(pcp, val) arch_this_cpu_write(pcp, val, "stc")
+#define this_cpu_write_2(pcp, val) arch_this_cpu_write(pcp, val, "sth")
+#define this_cpu_write_4(pcp, val) arch_this_cpu_write(pcp, val, "st")
+#define this_cpu_write_8(pcp, val) arch_this_cpu_write(pcp, val, "stg")
+
#define arch_this_cpu_cmpxchg(pcp, oval, nval) \
({ \
typedef typeof(pcp) pcp_op_T__; \
--
2.51.0