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Commit 8c49d9a7 authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Thomas Gleixner
Browse files

x86-64: Clean up vdso/kernel shared variables 



Variables that are shared between the vdso and the kernel are
currently a bit of a mess.  They are each defined with their own
magic, they are accessed differently in the kernel, the vsyscall page,
and the vdso, and one of them (vsyscall_clock) doesn't even really
exist.

This changes them all to use a common mechanism.  All of them are
delcared in vvar.h with a fixed address (validated by the linker
script).  In the kernel (as before), they look like ordinary
read-write variables.  In the vsyscall page and the vdso, they are
accessed through a new macro VVAR, which gives read-only access.

The vdso is now loaded verbatim into memory without any fixups.  As a
side bonus, access from the vdso is faster because a level of
indirection is removed.

While we're at it, pack jiffies and vgetcpu_mode into the same
cacheline.

Signed-off-by: default avatarAndy Lutomirski <luto@mit.edu>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Borislav Petkov <bp@amd64.org>
Link: http://lkml.kernel.org/r/%3C7357882fbb51fa30491636a7b6528747301b7ee9.1306156808.git.luto%40mit.edu%3E


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent d762f438

arch/x86/include/asm/vdso.h

+0 −14
Original line number Diff line number Diff line 
#ifndef _ASM_X86_VDSO_H

#define _ASM_X86_VDSO_H



#ifdef CONFIG_X86_64

extern const char VDSO64_PRELINK[];



/*

 * Given a pointer to the vDSO image, find the pointer to VDSO64_name

 * as that symbol is defined in the vDSO sources or linker script.

 */

#define VDSO64_SYMBOL(base, name)					\

({									\

	extern const char VDSO64_##name[];				\

	(void *)(VDSO64_##name - VDSO64_PRELINK + (unsigned long)(base)); \

})

#endif



#if defined CONFIG_X86_32 || defined CONFIG_COMPAT

extern const char VDSO32_PRELINK[];

arch/x86/include/asm/vgtod.h

+0 −2
Original line number Diff line number Diff line
@@ -23,8 +23,6 @@ struct vsyscall_gtod_data { 
	struct timespec wall_to_monotonic;

	struct timespec wall_time_coarse;

};

extern struct vsyscall_gtod_data __vsyscall_gtod_data

__section_vsyscall_gtod_data;

extern struct vsyscall_gtod_data vsyscall_gtod_data;



#endif /* _ASM_X86_VGTOD_H */

arch/x86/include/asm/vsyscall.h

+2 −10
Original line number Diff line number Diff line
@@ -16,27 +16,19 @@ enum vsyscall_num { 
#ifdef __KERNEL__

#include <linux/seqlock.h>



#define __section_vgetcpu_mode __attribute__ ((unused, __section__ (".vgetcpu_mode"), aligned(16)))

#define __section_jiffies __attribute__ ((unused, __section__ (".jiffies"), aligned(16)))



/* Definitions for CONFIG_GENERIC_TIME definitions */

#define __section_vsyscall_gtod_data __attribute__ \

	((unused, __section__ (".vsyscall_gtod_data"),aligned(16)))

#define __section_vsyscall_clock __attribute__ \

	((unused, __section__ (".vsyscall_clock"),aligned(16)))

#define __vsyscall_fn \

	__attribute__ ((unused, __section__(".vsyscall_fn"))) notrace



#define VGETCPU_RDTSCP	1

#define VGETCPU_LSL	2



extern int __vgetcpu_mode;

extern volatile unsigned long __jiffies;



/* kernel space (writeable) */

extern int vgetcpu_mode;

extern struct timezone sys_tz;



#include <asm/vvar.h>



extern void map_vsyscall(void);



#endif /* __KERNEL__ */

arch/x86/include/asm/vvar.h

0 → 100644
+52 −0
Original line number Diff line number Diff line 
/*

 * vvar.h: Shared vDSO/kernel variable declarations

 * Copyright (c) 2011 Andy Lutomirski

 * Subject to the GNU General Public License, version 2

 *

 * A handful of variables are accessible (read-only) from userspace

 * code in the vsyscall page and the vdso.  They are declared here.

 * Some other file must define them with DEFINE_VVAR.

 *

 * In normal kernel code, they are used like any other variable.

 * In user code, they are accessed through the VVAR macro.

 *

 * Each of these variables lives in the vsyscall page, and each

 * one needs a unique offset within the little piece of the page

 * reserved for vvars.  Specify that offset in DECLARE_VVAR.

 * (There are 896 bytes available.  If you mess up, the linker will

 * catch it.)

 */



/* Offset of vars within vsyscall page */

#define VSYSCALL_VARS_OFFSET (3072 + 128)



#if defined(__VVAR_KERNEL_LDS)



/* The kernel linker script defines its own magic to put vvars in the

 * right place.

 */

#define DECLARE_VVAR(offset, type, name) \

	EMIT_VVAR(name, VSYSCALL_VARS_OFFSET + offset)



#else



#define DECLARE_VVAR(offset, type, name)				\

	static type const * const vvaraddr_ ## name =			\

		(void *)(VSYSCALL_START + VSYSCALL_VARS_OFFSET + (offset));



#define DEFINE_VVAR(type, name)						\

	type __vvar_ ## name						\

	__attribute__((section(".vsyscall_var_" #name), aligned(16)))



#define VVAR(name) (*vvaraddr_ ## name)



#endif



/* DECLARE_VVAR(offset, type, name) */



DECLARE_VVAR(0, volatile unsigned long, jiffies)

DECLARE_VVAR(8, int, vgetcpu_mode)

DECLARE_VVAR(128, struct vsyscall_gtod_data, vsyscall_gtod_data)



#undef DECLARE_VVAR

#undef VSYSCALL_VARS_OFFSET

arch/x86/kernel/time.c

+1 −1
Original line number Diff line number Diff line
@@ -23,7 +23,7 @@ 
#include <asm/time.h>



#ifdef CONFIG_X86_64

volatile unsigned long __jiffies __section_jiffies = INITIAL_JIFFIES;

DEFINE_VVAR(volatile unsigned long, jiffies) = INITIAL_JIFFIES;

#endif



unsigned long profile_pc(struct pt_regs *regs)