[PATCH v3 4/5] arm64: vdso: Add getcpu() implementation

[Mark Brown <broonie@xxxxxxxxxx>]

Some applications, especially trace ones, benefit from avoiding the syscall
overhead on getcpu() calls so provide a vDSO implementation of it.

Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 arch/arm64/kernel/vdso/Makefile   |  2 +-
 arch/arm64/kernel/vdso/vdso.lds.S |  1 +
 arch/arm64/kernel/vdso/vgetcpu.c  | 48 +++++++++++++++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/kernel/vdso/vgetcpu.c

diff --git a/arch/arm64/kernel/vdso/Makefile b/arch/arm64/kernel/vdso/Makefile
index 88cf0f0b91ed..ff350e69b8b6 100644
--- a/arch/arm64/kernel/vdso/Makefile
+++ b/arch/arm64/kernel/vdso/Makefile
@@ -11,7 +11,7 @@
 ARCH_REL_TYPE_ABS := R_AARCH64_JUMP_SLOT|R_AARCH64_GLOB_DAT|R_AARCH64_ABS64
 include $(srctree)/lib/vdso/Makefile
 
-obj-vdso := vgettimeofday.o note.o sigreturn.o
+obj-vdso := vgettimeofday.o note.o sigreturn.o vgetcpu.o
 
 # Build rules
 targets := $(obj-vdso) vdso.so vdso.so.dbg
diff --git a/arch/arm64/kernel/vdso/vdso.lds.S b/arch/arm64/kernel/vdso/vdso.lds.S
index d808ad31e01f..ef3fb80e0349 100644
--- a/arch/arm64/kernel/vdso/vdso.lds.S
+++ b/arch/arm64/kernel/vdso/vdso.lds.S
@@ -80,6 +80,7 @@ VERSION
 		__kernel_gettimeofday;
 		__kernel_clock_gettime;
 		__kernel_clock_getres;
+		__kernel_getcpu;
 	local: *;
 	};
 }
diff --git a/arch/arm64/kernel/vdso/vgetcpu.c b/arch/arm64/kernel/vdso/vgetcpu.c
new file mode 100644
index 000000000000..e8972e561e08
--- /dev/null
+++ b/arch/arm64/kernel/vdso/vgetcpu.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * ARM64 userspace implementations of getcpu()
+ *
+ * Copyright (C) 2020 ARM Limited
+ *
+ */
+
+#include <asm/unistd.h>
+#include <asm/vdso/datapage.h>
+
+struct getcpucache;
+
+static __always_inline
+int getcpu_fallback(unsigned int *_cpu, unsigned int *_node,
+		    struct getcpucache *_c)
+{
+	register unsigned int *cpu asm("x0") = _cpu;
+	register unsigned int *node asm("x1") = _node;
+	register struct getcpucache *c asm("x2") = _c;
+	register long ret asm ("x0");
+	register long nr asm("x8") = __NR_getcpu;
+
+	asm volatile(
+	"       svc #0\n"
+	: "=r" (ret)
+	: "r" (cpu), "r" (node), "r" (c), "r" (nr)
+	: "memory");
+
+	return ret;
+}
+
+int __kernel_getcpu(unsigned int *cpu, unsigned int *node,
+		    struct getcpucache *c)
+{
+	struct vdso_cpu_data *cpu_data = __vdso_cpu_data();
+
+	if (cpu_data) {
+		if (cpu)
+			*cpu = cpu_data->cpu;
+		if (node)
+			*node = cpu_data->node;
+
+		return 0;
+	}
+
+	return getcpu_fallback(cpu, node, c);
+}
-- 
2.20.1