x86: load pointer to pda into %gs while brining up a CPU

[ Based on original patch from Christoph Lameter and Mike Travis. ]

CPU startup code in head_64.S loaded address of a zero page into %gs
for temporary use till pda is loaded but address to the actual pda is
available at the point.  Load the real address directly instead.

This will help unifying percpu and pda handling later on.

This patch is mostly taken from Mike Travis' "x86_64: Fold pda into
per cpu area" patch.

Signed-off-by: Tejun Heo <tj@kernel.org>

5 files changed, 15 insertions, 7 deletions

diff --git a/arch/x86/include/asm/trampoline.h b/arch/x86/include/asm/trampoline.h
index 780ba0a..90f06c2 100644
--- a/arch/x86/include/asm/trampoline.h
+++ b/arch/x86/include/asm/trampoline.h
@@ -13,6 +13,7 @@ extern unsigned char *trampoline_base;
 
 extern unsigned long init_rsp;
 extern unsigned long initial_code;
+extern unsigned long initial_gs;
 
 #define TRAMPOLINE_SIZE roundup(trampoline_end - trampoline_data, PAGE_SIZE)
 #define TRAMPOLINE_BASE 0x6000
diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 707c1f6..9ff67f8 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -101,6 +101,7 @@ int acpi_save_state_mem(void)
 	stack_start.sp = temp_stack + sizeof(temp_stack);
 	early_gdt_descr.address =
 			(unsigned long)get_cpu_gdt_table(smp_processor_id());
+	initial_gs = (unsigned long)cpu_pda(smp_processor_id());
 #endif
 	initial_code = (unsigned long)wakeup_long64;
 	saved_magic = 0x123456789abcdef0;
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index bc2900c..76ffba2 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -26,8 +26,8 @@
 #include <asm/bios_ebda.h>
 #include <asm/trampoline.h>
 
-/* boot cpu pda */
-static struct x8664_pda _boot_cpu_pda;
+/* boot cpu pda, referenced by head_64.S to initialize %gs for boot CPU */
+struct x8664_pda _boot_cpu_pda;
 
 #ifdef CONFIG_SMP
 /*
diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
index 7ee0363..2f0ab00 100644
--- a/arch/x86/kernel/head_64.S
+++ b/arch/x86/kernel/head_64.S
@@ -243,12 +243,15 @@ 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.
+	 *
+	 * %gs should point to the pda.  For initial boot, make %gs point
+	 * to the _boot_cpu_pda in data section.  For a secondary CPU,
+	 * initial_gs should be set to its pda address before the CPU runs
+	 * this code.
+	 */
 	movl	$MSR_GS_BASE,%ecx
-	movq	$empty_zero_page,%rax
+	movq	initial_gs(%rip),%rax
 	movq    %rax,%rdx
 	shrq	$32,%rdx
 	wrmsr	
@@ -274,6 +277,8 @@ ENTRY(secondary_startup_64)
 	.align	8
 	ENTRY(initial_code)
 	.quad	x86_64_start_kernel
+	ENTRY(initial_gs)
+	.quad	_boot_cpu_pda
 	__FINITDATA
 
 	ENTRY(stack_start)
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 1a712da..70d8466 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -854,6 +854,7 @@ do_rest:
 #else
 	cpu_pda(cpu)->pcurrent = c_idle.idle;
 	clear_tsk_thread_flag(c_idle.idle, TIF_FORK);
+	initial_gs = (unsigned long)cpu_pda(cpu);
 #endif
 	early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
 	initial_code = (unsigned long)start_secondary;