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x86-64: Clean up vdso/kernel shared variables

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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: Andy 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: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Andy Lutomirski 2011-05-23 09:31:24 -04:00 committed by Thomas Gleixner
parent d762f43831
commit 8c49d9a74b
15 changed files with 91 additions and 145 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
arch/x86/include/asm/vdso.h
View File

@ -1,20 +1,6 @@
#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[];

2
arch/x86/include/asm/vgtod.h
View File

@ -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 */

12
arch/x86/include/asm/vsyscall.h
View File

@ -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__ */

52
arch/x86/include/asm/vvar.h Normal file
View File

@ -0,0 +1,52 @@
/*
* 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

2
arch/x86/kernel/time.c
View File

@ -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)

4
arch/x86/kernel/tsc.c
View File

@ -777,8 +777,8 @@ static cycle_t __vsyscall_fn vread_tsc(void)
ret = (cycle_t)vget_cycles();
rdtsc_barrier();
return ret >= __vsyscall_gtod_data.clock.cycle_last ?
ret : __vsyscall_gtod_data.clock.cycle_last;
return ret >= VVAR(vsyscall_gtod_data).clock.cycle_last ?
ret : VVAR(vsyscall_gtod_data).clock.cycle_last;
}
#endif

34
arch/x86/kernel/vmlinux.lds.S
View File

@ -161,6 +161,12 @@ SECTIONS
#define VVIRT_OFFSET (VSYSCALL_ADDR - __vsyscall_0)
#define VVIRT(x) (ADDR(x) - VVIRT_OFFSET)
#define EMIT_VVAR(x, offset) .vsyscall_var_ ## x \
ADDR(.vsyscall_0) + offset \
: AT(VLOAD(.vsyscall_var_ ## x)) { \
*(.vsyscall_var_ ## x) \
} \
x = VVIRT(.vsyscall_var_ ## x);
. = ALIGN(4096);
__vsyscall_0 = .;
@ -175,18 +181,6 @@ SECTIONS
*(.vsyscall_fn)
}
. = ALIGN(L1_CACHE_BYTES);
.vsyscall_gtod_data : AT(VLOAD(.vsyscall_gtod_data)) {
*(.vsyscall_gtod_data)
}
vsyscall_gtod_data = VVIRT(.vsyscall_gtod_data);
.vsyscall_clock : AT(VLOAD(.vsyscall_clock)) {
*(.vsyscall_clock)
}
vsyscall_clock = VVIRT(.vsyscall_clock);
.vsyscall_1 ADDR(.vsyscall_0) + 1024: AT(VLOAD(.vsyscall_1)) {
*(.vsyscall_1)
}
@ -194,21 +188,14 @@ SECTIONS
*(.vsyscall_2)
}
.vgetcpu_mode : AT(VLOAD(.vgetcpu_mode)) {
*(.vgetcpu_mode)
}
vgetcpu_mode = VVIRT(.vgetcpu_mode);
. = ALIGN(L1_CACHE_BYTES);
.jiffies : AT(VLOAD(.jiffies)) {
*(.jiffies)
}
jiffies = VVIRT(.jiffies);
.vsyscall_3 ADDR(.vsyscall_0) + 3072: AT(VLOAD(.vsyscall_3)) {
*(.vsyscall_3)
}
#define __VVAR_KERNEL_LDS
#include <asm/vvar.h>
#undef __VVAR_KERNEL_LDS
. = __vsyscall_0 + PAGE_SIZE;
#undef VSYSCALL_ADDR
@ -216,6 +203,7 @@ SECTIONS
#undef VLOAD
#undef VVIRT_OFFSET
#undef VVIRT
#undef EMIT_VVAR
#endif /* CONFIG_X86_64 */

46
arch/x86/kernel/vsyscall_64.c
View File

@ -49,15 +49,8 @@
__attribute__ ((unused, __section__(".vsyscall_" #nr))) notrace
#define __syscall_clobber "r11","cx","memory"
/*
* vsyscall_gtod_data contains data that is :
* - readonly from vsyscalls
* - written by timer interrupt or systcl (/proc/sys/kernel/vsyscall64)
* Try to keep this structure as small as possible to avoid cache line ping pongs
*/
int __vgetcpu_mode __section_vgetcpu_mode;
struct vsyscall_gtod_data __vsyscall_gtod_data __section_vsyscall_gtod_data =
DEFINE_VVAR(int, vgetcpu_mode);
DEFINE_VVAR(struct vsyscall_gtod_data, vsyscall_gtod_data) =
{
.lock = SEQLOCK_UNLOCKED,
.sysctl_enabled = 1,
@ -97,7 +90,7 @@ void update_vsyscall(struct timespec *wall_time, struct timespec *wtm,
*/
static __always_inline void do_get_tz(struct timezone * tz)
{
*tz = __vsyscall_gtod_data.sys_tz;
*tz = VVAR(vsyscall_gtod_data).sys_tz;
}
static __always_inline int gettimeofday(struct timeval *tv, struct timezone *tz)
@ -126,23 +119,24 @@ static __always_inline void do_vgettimeofday(struct timeval * tv)
unsigned long mult, shift, nsec;
cycle_t (*vread)(void);
do {
seq = read_seqbegin(&__vsyscall_gtod_data.lock);
seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);
vread = __vsyscall_gtod_data.clock.vread;
if (unlikely(!__vsyscall_gtod_data.sysctl_enabled || !vread)) {
vread = VVAR(vsyscall_gtod_data).clock.vread;
if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled ||
!vread)) {
gettimeofday(tv,NULL);
return;
}
now = vread();
base = __vsyscall_gtod_data.clock.cycle_last;
mask = __vsyscall_gtod_data.clock.mask;
mult = __vsyscall_gtod_data.clock.mult;
shift = __vsyscall_gtod_data.clock.shift;
base = VVAR(vsyscall_gtod_data).clock.cycle_last;
mask = VVAR(vsyscall_gtod_data).clock.mask;
mult = VVAR(vsyscall_gtod_data).clock.mult;
shift = VVAR(vsyscall_gtod_data).clock.shift;
tv->tv_sec = __vsyscall_gtod_data.wall_time_sec;
nsec = __vsyscall_gtod_data.wall_time_nsec;
} while (read_seqretry(&__vsyscall_gtod_data.lock, seq));
tv->tv_sec = VVAR(vsyscall_gtod_data).wall_time_sec;
nsec = VVAR(vsyscall_gtod_data).wall_time_nsec;
} while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));
/* calculate interval: */
cycle_delta = (now - base) & mask;
@ -171,15 +165,15 @@ time_t __vsyscall(1) vtime(time_t *t)
{
unsigned seq;
time_t result;
if (unlikely(!__vsyscall_gtod_data.sysctl_enabled))
if (unlikely(!VVAR(vsyscall_gtod_data).sysctl_enabled))
return time_syscall(t);
do {
seq = read_seqbegin(&__vsyscall_gtod_data.lock);
seq = read_seqbegin(&VVAR(vsyscall_gtod_data).lock);
result = __vsyscall_gtod_data.wall_time_sec;
result = VVAR(vsyscall_gtod_data).wall_time_sec;
} while (read_seqretry(&__vsyscall_gtod_data.lock, seq));
} while (read_seqretry(&VVAR(vsyscall_gtod_data).lock, seq));
if (t)
*t = result;
@ -208,9 +202,9 @@ vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
We do this here because otherwise user space would do it on
its own in a likely inferior way (no access to jiffies).
If you don't like it pass NULL. */
if (tcache && tcache->blob[0] == (j = __jiffies)) {
if (tcache && tcache->blob[0] == (j = VVAR(jiffies))) {
p = tcache->blob[1];
} else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
} else if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
native_read_tscp(&p);
} else {

2
arch/x86/vdso/Makefile
View File

@ -11,7 +11,7 @@ vdso-install-$(VDSO32-y) += $(vdso32-images)
# files to link into the vdso
vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o vvar.o
vobjs-y := vdso-note.o vclock_gettime.o vgetcpu.o
# files to link into kernel
obj-$(VDSO64-y) += vma.o vdso.o

3
arch/x86/vdso/vclock_gettime.c
View File

@ -22,9 +22,8 @@
#include <asm/hpet.h>
#include <asm/unistd.h>
#include <asm/io.h>
#include "vextern.h"
#define gtod vdso_vsyscall_gtod_data
#define gtod (&VVAR(vsyscall_gtod_data))
notrace static long vdso_fallback_gettime(long clock, struct timespec *ts)
{

7
arch/x86/vdso/vdso.lds.S
View File

@ -28,10 +28,3 @@ VERSION {
}
VDSO64_PRELINK = VDSO_PRELINK;
/*
* Define VDSO64_x for each VEXTERN(x), for use via VDSO64_SYMBOL.
*/
#define VEXTERN(x) VDSO64_ ## x = vdso_ ## x;
#include "vextern.h"
#undef VEXTERN

16
arch/x86/vdso/vextern.h
View File

@ -1,16 +0,0 @@
#ifndef VEXTERN
#include <asm/vsyscall.h>
#define VEXTERN(x) \
extern typeof(x) *vdso_ ## x __attribute__((visibility("hidden")));
#endif
#define VMAGIC 0xfeedbabeabcdefabUL
/* Any kernel variables used in the vDSO must be exported in the main
kernel's vmlinux.lds.S/vsyscall.h/proper __section and
put into vextern.h and be referenced as a pointer with vdso prefix.
The main kernel later fills in the values. */
VEXTERN(jiffies)
VEXTERN(vgetcpu_mode)
VEXTERN(vsyscall_gtod_data)

3
arch/x86/vdso/vgetcpu.c
View File

@ -11,14 +11,13 @@
#include <linux/time.h>
#include <asm/vsyscall.h>
#include <asm/vgtod.h>
#include "vextern.h"
notrace long
__vdso_getcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *unused)
{
unsigned int p;
if (*vdso_vgetcpu_mode == VGETCPU_RDTSCP) {
if (VVAR(vgetcpu_mode) == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
native_read_tscp(&p);
} else {

27
arch/x86/vdso/vma.c
View File

@ -15,9 +15,6 @@
#include <asm/proto.h>
#include <asm/vdso.h>
#include "vextern.h" /* Just for VMAGIC. */
#undef VEXTERN
unsigned int __read_mostly vdso_enabled = 1;
extern char vdso_start[], vdso_end[];
@ -26,20 +23,10 @@ extern unsigned short vdso_sync_cpuid;
static struct page **vdso_pages;
static unsigned vdso_size;
static inline void *var_ref(void *p, char *name)
{
if (*(void **)p != (void *)VMAGIC) {
printk("VDSO: variable %s broken\n", name);
vdso_enabled = 0;
}
return p;
}
static int __init init_vdso_vars(void)
{
int npages = (vdso_end - vdso_start + PAGE_SIZE - 1) / PAGE_SIZE;
int i;
char *vbase;
vdso_size = npages << PAGE_SHIFT;
vdso_pages = kmalloc(sizeof(struct page *) * npages, GFP_KERNEL);
@ -54,20 +41,6 @@ static int __init init_vdso_vars(void)
copy_page(page_address(p), vdso_start + i*PAGE_SIZE);
}
vbase = vmap(vdso_pages, npages, 0, PAGE_KERNEL);
if (!vbase)
goto oom;
if (memcmp(vbase, "\177ELF", 4)) {
printk("VDSO: I'm broken; not ELF\n");
vdso_enabled = 0;
}
#define VEXTERN(x) \
*(typeof(__ ## x) **) var_ref(VDSO64_SYMBOL(vbase, x), #x) = &__ ## x;
#include "vextern.h"
#undef VEXTERN
vunmap(vbase);
return 0;
oom:

12
arch/x86/vdso/vvar.c
View File

@ -1,12 +0,0 @@
/* Define pointer to external vDSO variables.
These are part of the vDSO. The kernel fills in the real addresses
at boot time. This is done because when the vdso is linked the
kernel isn't yet and we don't know the final addresses. */
#include <linux/kernel.h>
#include <linux/time.h>
#include <asm/vsyscall.h>
#include <asm/timex.h>
#include <asm/vgtod.h>
#define VEXTERN(x) typeof (__ ## x) *const vdso_ ## x = (void *)VMAGIC;
#include "vextern.h"