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: 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>

15 files changed, 91 insertions, 145 deletions

diff --git a/arch/x86/include/asm/vdso.h b/arch/x86/include/asm/vdso.h
index 9064052b73de..bb0522850b74 100644
--- a/arch/x86/include/asm/vdso.h
+++ b/arch/x86/include/asm/vdso.h
@@ -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[];
 
diff --git a/arch/x86/include/asm/vgtod.h b/arch/x86/include/asm/vgtod.h
index 3d61e204826f..646b4c1ca695 100644
--- a/arch/x86/include/asm/vgtod.h
+++ b/arch/x86/include/asm/vgtod.h
@@ -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 */
diff --git a/arch/x86/include/asm/vsyscall.h b/arch/x86/include/asm/vsyscall.h
index d0983d255fbd..d55597351f6a 100644
--- a/arch/x86/include/asm/vsyscall.h
+++ b/arch/x86/include/asm/vsyscall.h
@@ -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__ */
diff --git a/arch/x86/include/asm/vvar.h b/arch/x86/include/asm/vvar.h
new file mode 100644
index 000000000000..341b3559452b
--- /dev/null
+++ b/arch/x86/include/asm/vvar.h
@@ -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
diff --git a/arch/x86/kernel/time.c b/arch/x86/kernel/time.c
index 25a28a245937..00cbb272627f 100644
--- a/arch/x86/kernel/time.c
+++ b/arch/x86/kernel/time.c
@@ -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)
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 9335bf7dd2e7..db697b81b8b1 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -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
 
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 49927a863cc1..74b5ad450c7e 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -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 */
 
diff --git a/arch/x86/kernel/vsyscall_64.c b/arch/x86/kernel/vsyscall_64.c
index dcbb28c4b694..5f6ad032575a 100644
--- a/arch/x86/kernel/vsyscall_64.c
+++ b/arch/x86/kernel/vsyscall_64.c
@@ -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 {
diff --git a/arch/x86/vdso/Makefile b/arch/x86/vdso/Makefile
index b6552b189bcd..a651861f7e8e 100644
--- a/arch/x86/vdso/Makefile
+++ b/arch/x86/vdso/Makefile
@@ -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
diff --git a/arch/x86/vdso/vclock_gettime.c b/arch/x86/vdso/vclock_gettime.c
index ee55754cc3c5..0b873d455bda 100644
--- a/arch/x86/vdso/vclock_gettime.c
+++ b/arch/x86/vdso/vclock_gettime.c
@@ -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)
 {
diff --git a/arch/x86/vdso/vdso.lds.S b/arch/x86/vdso/vdso.lds.S
index 4e5dd3b4de7f..81f250011f71 100644
--- a/arch/x86/vdso/vdso.lds.S
+++ b/arch/x86/vdso/vdso.lds.S
@@ -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
diff --git a/arch/x86/vdso/vextern.h b/arch/x86/vdso/vextern.h
deleted file mode 100644
index 1683ba2ae3e8..000000000000
--- a/arch/x86/vdso/vextern.h
+++ /dev/null
@@ -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)
diff --git a/arch/x86/vdso/vgetcpu.c b/arch/x86/vdso/vgetcpu.c
index 9fbc6b20026b..5463ad558573 100644
--- a/arch/x86/vdso/vgetcpu.c
+++ b/arch/x86/vdso/vgetcpu.c
@@ -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 {
diff --git a/arch/x86/vdso/vma.c b/arch/x86/vdso/vma.c
index 4b5d26f108bb..7abd2be0f9b9 100644
--- a/arch/x86/vdso/vma.c
+++ b/arch/x86/vdso/vma.c
@@ -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:
diff --git a/arch/x86/vdso/vvar.c b/arch/x86/vdso/vvar.c
deleted file mode 100644
index 1b7e703684f9..000000000000
--- a/arch/x86/vdso/vvar.c
+++ /dev/null
@@ -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"