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

Signed-off-by: Andi Kleen <ak@suse.de>

diff --git a/arch/x86_64/kernel/vsyscall.c b/arch/x86_64/kernel/vsyscall.c
index ac48c38..07c0863 100644 (file)
--- a/arch/x86_64/kernel/vsyscall.c
+++ b/arch/x86_64/kernel/vsyscall.c
@@ -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;

diff --git a/include/linux/getcpu.h b/include/linux/getcpu.h
index 031ed37..c7372d7 100644 (file)
--- a/include/linux/getcpu.h
+++ b/include/linux/getcpu.h
@@ -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    out of date, but will be faster.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

diff --git a/kernel/sys.c b/kernel/sys.c
index 8647061..b88806c 100644 (file)
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -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;
 }