Commit 7c3576d2 authored by Jeremy Fitzhardinge's avatar Jeremy Fitzhardinge Committed by Andi Kleen
Browse files

[PATCH] i386: Convert PDA into the percpu section 



Currently x86 (similar to x84-64) has a special per-cpu structure
called "i386_pda" which can be easily and efficiently referenced via
the %fs register.  An ELF section is more flexible than a structure,
allowing any piece of code to use this area.  Indeed, such a section
already exists: the per-cpu area.

So this patch:
(1) Removes the PDA and uses per-cpu variables for each current member.
(2) Replaces the __KERNEL_PDA segment with __KERNEL_PERCPU.
(3) Creates a per-cpu mirror of __per_cpu_offset called this_cpu_off, which
    can be used to calculate addresses for this CPU's variables.
(4) Simplifies startup, because %fs doesn't need to be loaded with a
    special segment at early boot; it can be deferred until the first
    percpu area is allocated (or never for UP).

The result is less code and one less x86-specific concept.

Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarJeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: default avatarAndi Kleen <ak@suse.de>
Cc: Andi Kleen <ak@suse.de>
parent 7a61d35d

arch/i386/kernel/asm-offsets.c

+0 −5
Original line number Diff line number Diff line
@@ -15,7 +15,6 @@ 
#include <asm/processor.h>

#include <asm/thread_info.h>

#include <asm/elf.h>

#include <asm/pda.h>



#define DEFINE(sym, val) \

        asm volatile("\n->" #sym " %0 " #val : : "i" (val))
@@ -101,10 +100,6 @@ void foo(void) 


	OFFSET(crypto_tfm_ctx_offset, crypto_tfm, __crt_ctx);



	BLANK();

 	OFFSET(PDA_cpu, i386_pda, cpu_number);

	OFFSET(PDA_pcurrent, i386_pda, pcurrent);



#ifdef CONFIG_PARAVIRT

	BLANK();

	OFFSET(PARAVIRT_enabled, paravirt_ops, paravirt_enabled);

arch/i386/kernel/cpu/common.c

+3 −14
Original line number Diff line number Diff line
@@ -18,7 +18,6 @@ 
#include <asm/apic.h>

#include <mach_apic.h>

#endif

#include <asm/pda.h>



#include "cpu.h"
@@ -47,13 +46,10 @@ DEFINE_PER_CPU(struct gdt_page, gdt_page) = { .gdt = { 
	[GDT_ENTRY_APMBIOS_BASE+2] = { 0x0000ffff, 0x00409200 }, /* data */



	[GDT_ENTRY_ESPFIX_SS] = { 0x00000000, 0x00c09200 },

	[GDT_ENTRY_PDA] = { 0x00000000, 0x00c09200 }, /* set in setup_pda */

	[GDT_ENTRY_PERCPU] = { 0x00000000, 0x00000000 },

} };

EXPORT_PER_CPU_SYMBOL_GPL(gdt_page);



DEFINE_PER_CPU(struct i386_pda, _cpu_pda);

EXPORT_PER_CPU_SYMBOL(_cpu_pda);



static int cachesize_override __cpuinitdata = -1;

static int disable_x86_fxsr __cpuinitdata;

static int disable_x86_serial_nr __cpuinitdata = 1;
@@ -634,21 +630,14 @@ void __init early_cpu_init(void) 
#endif

}



/* Make sure %gs is initialized properly in idle threads */

/* Make sure %fs is initialized properly in idle threads */

struct pt_regs * __devinit idle_regs(struct pt_regs *regs)

{

	memset(regs, 0, sizeof(struct pt_regs));

	regs->xfs = __KERNEL_PDA;

	regs->xfs = __KERNEL_PERCPU;

	return regs;

}



/* Initial PDA used by boot CPU */

struct i386_pda boot_pda = {

	._pda = &boot_pda,

	.cpu_number = 0,

	.pcurrent = &init_task,

};



/*

 * cpu_init() initializes state that is per-CPU. Some data is already

 * initialized (naturally) in the bootstrap process, such as the GDT

arch/i386/kernel/entry.S

+2 −3
Original line number Diff line number Diff line
@@ -132,7 +132,7 @@ VM_MASK = 0x00020000 
	movl $(__USER_DS), %edx; \

	movl %edx, %ds; \

	movl %edx, %es; \

	movl $(__KERNEL_PDA), %edx; \

	movl $(__KERNEL_PERCPU), %edx; \

	movl %edx, %fs



#define RESTORE_INT_REGS \
@@ -556,7 +556,6 @@ END(syscall_badsys) 


#define FIXUP_ESPFIX_STACK \

	/* since we are on a wrong stack, we cant make it a C code :( */ \

	movl %fs:PDA_cpu, %ebx; \

	PER_CPU(gdt_page, %ebx); \

	GET_DESC_BASE(GDT_ENTRY_ESPFIX_SS, %ebx, %eax, %ax, %al, %ah); \

	addl %esp, %eax; \
@@ -681,7 +680,7 @@ error_code: 
	pushl %fs

	CFI_ADJUST_CFA_OFFSET 4

	/*CFI_REL_OFFSET fs, 0*/

	movl $(__KERNEL_PDA), %ecx

	movl $(__KERNEL_PERCPU), %ecx

	movl %ecx, %fs

	UNWIND_ESPFIX_STACK

	popl %ecx

arch/i386/kernel/head.S

+6 −25
Original line number Diff line number Diff line
@@ -317,12 +317,12 @@ is386: movl $2,%ecx # set MP 
	movl %eax,%cr0



	call check_x87

	call setup_pda

	lgdt early_gdt_descr

	lidt idt_descr

	ljmp $(__KERNEL_CS),$1f

1:	movl $(__KERNEL_DS),%eax	# reload all the segment registers

	movl %eax,%ss			# after changing gdt.

	movl %eax,%fs			# gets reset once there's real percpu



	movl $(__USER_DS),%eax		# DS/ES contains default USER segment

	movl %eax,%ds
@@ -332,16 +332,17 @@ is386: movl $2,%ecx # set MP 
	movl %eax,%gs

	lldt %ax



	movl $(__KERNEL_PDA),%eax

	mov  %eax,%fs



	cld			# gcc2 wants the direction flag cleared at all times

	pushl $0		# fake return address for unwinder

#ifdef CONFIG_SMP

	movb ready, %cl

	movb $1, ready

	cmpb $0,%cl		# the first CPU calls start_kernel

	jne initialize_secondary # all other CPUs call initialize_secondary

	je   1f

	movl $(__KERNEL_PERCPU), %eax

	movl %eax,%fs		# set this cpu's percpu

	jmp initialize_secondary # all other CPUs call initialize_secondary

1:

#endif /* CONFIG_SMP */

	jmp start_kernel
@@ -364,23 +365,6 @@ check_x87: 
	.byte 0xDB,0xE4		/* fsetpm for 287, ignored by 387 */

	ret



/*

 * Point the GDT at this CPU's PDA.  On boot this will be

 * cpu_gdt_table and boot_pda; for secondary CPUs, these will be

 * that CPU's GDT and PDA.

 */

ENTRY(setup_pda)

	/* get the PDA pointer */

	movl start_pda, %eax



	/* slot the PDA address into the GDT */

	mov early_gdt_descr+2, %ecx

	mov %ax, (__KERNEL_PDA+0+2)(%ecx)		/* base & 0x0000ffff */

	shr $16, %eax

	mov %al, (__KERNEL_PDA+4+0)(%ecx)		/* base & 0x00ff0000 */

	mov %ah, (__KERNEL_PDA+4+3)(%ecx)		/* base & 0xff000000 */

	ret



/*

 *  setup_idt

 *
@@ -553,9 +537,6 @@ ENTRY(empty_zero_page) 
 * This starts the data section.

 */

.data

ENTRY(start_pda)

	.long boot_pda



ENTRY(stack_start)

	.long init_thread_union+THREAD_SIZE

	.long __BOOT_DS

arch/i386/kernel/i386_ksyms.c

+0 −2
Original line number Diff line number Diff line
@@ -28,5 +28,3 @@ EXPORT_SYMBOL(__read_lock_failed); 
#endif



EXPORT_SYMBOL(csum_partial);
 


EXPORT_SYMBOL(_proxy_pda);

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