1 files changed, 41 insertions, 6 deletions

diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 0e275d495563..c8ace880661b 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -19,6 +19,7 @@
 #include <asm/msr.h>
 #include <asm/cache.h>
 #include <asm/processor-flags.h>
+#include <asm/percpu.h>
 
 #ifdef CONFIG_PARAVIRT
 #include <asm/asm-offsets.h>
@@ -204,6 +205,23 @@ ENTRY(secondary_startup_64)
         pushq $0
         popfq
 
+#ifdef CONFIG_SMP
+        /*
+         * early_gdt_base should point to the gdt_page in static percpu init
+         * data area.  Computing this requires two symbols - __per_cpu_load
+         * and per_cpu__gdt_page.  As linker can't do no such relocation, do
+         * it by hand.  As early_gdt_descr is manipulated by C code for
+         * secondary CPUs, this should be done only once for the boot CPU
+         * when early_gdt_descr_base contains zero.
+         */
+        movq    early_gdt_descr_base(%rip), %rax
+        testq   %rax, %rax
+        jnz     1f
+        movq    $__per_cpu_load, %rax
+        addq    $per_cpu__gdt_page, %rax
+        movq    %rax, early_gdt_descr_base(%rip)
+1:
+#endif
         /*
          * We must switch to a new descriptor in kernel space for the GDT
          * because soon the kernel won't have access anymore to the userspace
@@ -226,12 +244,18 @@ ENTRY(secondary_startup_64)
         movl %eax,%fs
         movl %eax,%gs
 
-        /* 
-         * Setup up a dummy PDA. this is just for some early bootup code
-         * that does in_interrupt() 
-         */ 
+        /* Set up %gs.
+         *
+         * On SMP, %gs should point to the per-cpu area.  For initial
+         * boot, make %gs point to the init data section.  For a
+         * secondary CPU,initial_gs should be set to its pda address
+         * before the CPU runs this code.
+         *
+         * On UP, initial_gs points to PER_CPU_VAR(__pda) and doesn't
+         * change.
+         */
         movl    $MSR_GS_BASE,%ecx
-        movq    $empty_zero_page,%rax
+        movq    initial_gs(%rip),%rax
         movq    %rax,%rdx
         shrq    $32,%rdx
         wrmsr   
@@ -257,6 +281,12 @@ ENTRY(secondary_startup_64)
         .align  8
         ENTRY(initial_code)
         .quad   x86_64_start_kernel
+        ENTRY(initial_gs)
+#ifdef CONFIG_SMP
+        .quad   __per_cpu_load
+#else
+        .quad   PER_CPU_VAR(__pda)
+#endif
         __FINITDATA
 
         ENTRY(stack_start)
@@ -401,7 +431,12 @@ NEXT_PAGE(level2_spare_pgt)
         .globl early_gdt_descr
 early_gdt_descr:
         .word   GDT_ENTRIES*8-1
-        .quad   per_cpu__gdt_page
+#ifdef CONFIG_SMP
+early_gdt_descr_base:
+        .quad   0x0000000000000000
+#else
+        .quad   per_cpu__gdt_page
+#endif
 
 ENTRY(phys_base)
         /* This must match the first entry in level2_kernel_pgt */