[PATCH] x86_64 : Suppress __jiffies

Eric Dumazet
2007-03-19T21:56:01Z

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Hi Andi

I was considering re-submiting patch to group together
xtime_lock/xtime/jiffies in the same cache line. Before doing so, I believe
the following cleanup patch could prepare the x86_64 port to be similar with
other arches.

Thank you

[PATCH] x86_64 : Suppress __jiffies

x86_64 arch currently specially defines __jiffies, as a relic of old vsyscall
implementation. It is currently used to validate vgetcpu() user cache as a
token. If we use another token, more opaque like the seqlock sequence, we can
get rid of special __jiffies handling. As a result, jiffies_64 is no more
included in vsyscall page. This patch prepares the introduction of time_data.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>

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diff --git a/arch/x86_64/kernel/vsyscall.c b/arch/x86_64/kernel/vsyscall.c
index b43c698..ac4d865 100644
--- a/arch/x86_64/kernel/vsyscall.c
+++ b/arch/x86_64/kernel/vsyscall.c
@@ -62,6 +62,14 @@ struct vsyscall_gtod_data_t __vsyscall_g
.sysctl_enabled = 1,
};

+/*
+ * vgetcpu_token is an opaque token used to validate vgetcpu() user cache.
+ * We need something that change like jiffies. It used to be jiffies
+ * but using seqlock __vsyscall_gtod_data.lock sequence is better because
+ * we prefer not let user read jiffies.
+ */
+#define vgetcpu_token() read_seqbegin(&__vsyscall_gtod_data.lock)
+
void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
{
unsigned long flags;
@@ -180,7 +188,7 @@ vgetcpu(unsigned *cpu, unsigned *node, s
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 = vgetcpu_token())) {
p = tcache->blob[1];
} else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 75d73a9..5a44c11 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -53,7 +53,6 @@ DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL(rtc_lock);
DEFINE_SPINLOCK(i8253_lock);

-volatile unsigned long __jiffies __section_jiffies = INITIAL_JIFFIES;

unsigned long profile_pc(struct pt_regs *regs)
{
diff --git a/arch/x86_64/kernel/vmlinux.lds.S b/arch/x86_64/kernel/vmlinux.lds.S
index b73212c..6ca4660 100644
--- a/arch/x86_64/kernel/vmlinux.lds.S
+++ b/arch/x86_64/kernel/vmlinux.lds.S
@@ -12,7 +12,7 @@ #undef i386 /* in case the preprocessor
OUTPUT_FORMAT("elf64-x86-64", "elf64-x86-64", "elf64-x86-64")
OUTPUT_ARCH(i386:x86-64)
ENTRY(phys_startup_64)
-jiffies_64 = jiffies;
+jiffies = jiffies_64;
_proxy_pda = 0;
PHDRS {
text PT_LOAD FLAGS(5); /* R_E */
@@ -97,10 +97,6 @@ #define VVIRT(x) (ADDR(x) - VVIRT_OFFSET
.vgetcpu_mode : AT(VLOAD(.vgetcpu_mode)) { *(.vgetcpu_mode) }
vgetcpu_mode = VVIRT(.vgetcpu_mode);

- . = ALIGN(CONFIG_X86_L1_CACHE_BYTES);
- .jiffies : AT(VLOAD(.jiffies)) { *(.jiffies) }
- jiffies = VVIRT(.jiffies);
-
.vsyscall_1 ADDR(.vsyscall_0) + 1024: AT(VLOAD(.vsyscall_1))
{ *(.vsyscall_1) }
.vsyscall_2 ADDR(.vsyscall_0) + 2048: AT(VLOAD(.vsyscall_2))
diff --git a/include/asm-x86_64/vsyscall.h b/include/asm-x86_64/vsyscall.h
index 82b4afe..1fb09dc 100644
--- a/include/asm-x86_64/vsyscall.h
+++ b/include/asm-x86_64/vsyscall.h
@@ -17,7 +17,6 @@ #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__ \
@@ -31,7 +30,6 @@ #define hpet_readl(a) readl((c
#define hpet_writel(d,a) writel(d, (void __iomem *)fix_to_virt(FIX_HPET_BASE) + a)

extern int __vgetcpu_mode;
-extern volatile unsigned long __jiffies;

/* kernel space (writeable) */
extern int vgetcpu_mode;