x86: split loading percpu segments from loading gdt

Impact: split out a function, no functional change

Xen needs to be able to access percpu data from very early on.  For
various reasons, it cannot also load the gdt at that time.   It does,
however, have a pefectly functional gdt at that point, so there's no
pressing need to reload the gdt.

Split the function to load the segment registers off, so Xen can call
it directly.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index 1c25eb69ea861bfc794c55a51b32f64c58a4ce07..656d02ea509b7b3ee226e209b060b59b8d520653 100644 (file)
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -769,6 +769,7 @@ extern struct desc_ptr              early_gdt_descr;
 
 extern void cpu_set_gdt(int);
 extern void switch_to_new_gdt(int);
+extern void load_percpu_segment(int);
 extern void cpu_init(void);
 
 static inline unsigned long get_debugctlmsr(void)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 6eacd64b602e273bbe73bf04eaa26c5d1c5867a3..0f73ea423089d53af3dfae07d13721ff78a669bb 100644 (file)
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -253,6 +253,16 @@ static char __cpuinit *table_lookup_model(struct cpuinfo_x86 *c)
 
 __u32 cleared_cpu_caps[NCAPINTS] __cpuinitdata;
 
+void load_percpu_segment(int cpu)
+{
+#ifdef CONFIG_X86_32
+       loadsegment(fs, __KERNEL_PERCPU);
+#else
+       loadsegment(gs, 0);
+       wrmsrl(MSR_GS_BASE, (unsigned long)per_cpu(irq_stack_union.gs_base, cpu));
+#endif
+}
+
 /* Current gdt points %fs at the "master" per-cpu area: after this,
  * it's on the real one. */
 void switch_to_new_gdt(int cpu)
@@ -263,12 +273,8 @@ void switch_to_new_gdt(int cpu)
        gdt_descr.size = GDT_SIZE - 1;
        load_gdt(&gdt_descr);
        /* Reload the per-cpu base */
-#ifdef CONFIG_X86_32
-       loadsegment(fs, __KERNEL_PERCPU);
-#else
-       loadsegment(gs, 0);
-       wrmsrl(MSR_GS_BASE, (unsigned long)per_cpu(irq_stack_union.gs_base, cpu));
-#endif
+
+       load_percpu_segment(cpu);
 }
 
 static struct cpu_dev *cpu_devs[X86_VENDOR_NUM] = {};