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Commit 34596dc9 authored by Andi Kleen's avatar Andi Kleen Committed by Andi Kleen
Browse files

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



Signed-off-by: default avatarAndi Kleen <ak@suse.de>
parent 120b1142

arch/x86_64/kernel/vsyscall.c

+4 −4
Original line number Diff line number Diff line
@@ -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;

include/linux/getcpu.h

+7 −5
Original line number Diff line number Diff line 
#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   out of date, but will be faster.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

kernel/sys.c

+4 −4
Original line number Diff line number Diff line
@@ -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;

}