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[PATCH] Define vsyscall cache as blob to make clearer that user space shouldn't use it

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Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
Andi Kleen 2006-09-30 01:47:55 +02:00 committed by Andi Kleen
parent 120b114237
commit 34596dc9e5
3 changed files with 15 additions and 13 deletions
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8
arch/x86_64/kernel/vsyscall.c
View file

@ -155,8 +155,8 @@ 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->t0 == (j = __jiffies)) {
p = tcache->t1;
if (tcache && tcache->blob[0] == (j = __jiffies)) {
p = tcache->blob[1];
} else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
rdtscp(dummy, dummy, p);
@ -165,8 +165,8 @@ vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
}
if (tcache) {
tcache->t0 = j;
tcache->t1 = p;
tcache->blob[0] = j;
tcache->blob[1] = p;
}
if (cpu)
*cpu = p & 0xfff;

12
include/linux/getcpu.h
View file

@ -1,16 +1,18 @@
#ifndef _LINUX_GETCPU_H
#define _LINUX_GETCPU_H 1
/* Cache for getcpu() to speed it up. Results might be upto a jiffie
/* Cache for getcpu() to speed it up. Results might be a short time
out of date, but will be faster.
User programs should not refer to the contents of this structure.
It is only a cache for vgetcpu(). It might change in future kernels.
I repeat they should not refer to it. If they do they will break
in future kernels.
It is only a private cache for vgetcpu(). It will change in future kernels.
The user program must store this information per thread (__thread)
If you want 100% accurate information pass NULL instead. */
struct getcpu_cache {
unsigned long t0;
unsigned long t1;
unsigned long res[4];
unsigned long blob[128 / sizeof(long)];
};
#endif

8
kernel/sys.c
View file

@ -2083,12 +2083,12 @@ asmlinkage long sys_getcpu(unsigned __user *cpup, unsigned __user *nodep,
* padding
*/
unsigned long t0, t1;
get_user(t0, &cache->t0);
get_user(t1, &cache->t1);
get_user(t0, &cache->blob[0]);
get_user(t1, &cache->blob[1]);
t0++;
t1++;
put_user(t0, &cache->t0);
put_user(t1, &cache->t1);
put_user(t0, &cache->blob[0]);
put_user(t1, &cache->blob[1]);
}
return err ? -EFAULT : 0;
}