[PATCH RFC 12/12] time: Convert pvclock_read_wallclock() to use timespec64

From: pang.xunlei
Date: Mon Oct 27 2014 - 01:48:00 EST


The kernel uses 32-bit signed value(time_t) for seconds since 1970-01-01:00:00:00, so it
will overflow at 2038-01-19 03:14:08 on 32-bit systems. We call this "2038 safety" issue.

As part of addressing 2038 safety for in-kernel uses, this patch creates no functional change
in existing users, converts pvclock_read_wallclock() to use timespec64 instead of timespec.

Signed-off-by: pang.xunlei <pang.xunlei@xxxxxxxxxx>
---
arch/x86/include/asm/pvclock.h | 2 +-
arch/x86/kernel/kvmclock.c | 7 +++++--
arch/x86/kernel/pvclock.c | 8 ++++----
arch/x86/xen/time.c | 10 ++--------
4 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/pvclock.h b/arch/x86/include/asm/pvclock.h
index d6b078e..3323413 100644
--- a/arch/x86/include/asm/pvclock.h
+++ b/arch/x86/include/asm/pvclock.h
@@ -11,7 +11,7 @@ void pvclock_set_flags(u8 flags);
unsigned long pvclock_tsc_khz(struct pvclock_vcpu_time_info *src);
void pvclock_read_wallclock(struct pvclock_wall_clock *wall,
struct pvclock_vcpu_time_info *vcpu,
- struct timespec *ts);
+ struct timespec64 *ts);
void pvclock_resume(void);

void pvclock_touch_watchdogs(void);
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index d9156ce..7cd3511 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -46,10 +46,12 @@ static struct pvclock_wall_clock wall_clock;
/*
* The wallclock is the time of day when we booted. Since then, some time may
* have elapsed since the hypervisor wrote the data. So we try to account for
- * that with system time
+ * that with system time.
+ * TODO: [2038 safety] kvm_get_wallclock() should be fixed to use timespec64.
*/
static void kvm_get_wallclock(struct timespec *now)
{
+ struct timespec64 now64;
struct pvclock_vcpu_time_info *vcpu_time;
int low, high;
int cpu;
@@ -63,7 +65,8 @@ static void kvm_get_wallclock(struct timespec *now)
cpu = smp_processor_id();

vcpu_time = &hv_clock[cpu].pvti;
- pvclock_read_wallclock(&wall_clock, vcpu_time, now);
+ pvclock_read_wallclock(&wall_clock, vcpu_time, &now64);
+ *now = timespec64_to_timespec(now64);

preempt_enable();
}
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 2f355d2..ae3ae07 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -117,17 +117,17 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)

void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
struct pvclock_vcpu_time_info *vcpu_time,
- struct timespec *ts)
+ struct timespec64 *ts)
{
u32 version;
u64 delta;
- struct timespec now;
+ struct timespec64 now;

/* get wallclock at system boot */
do {
version = wall_clock->version;
rmb(); /* fetch version before time */
- now.tv_sec = wall_clock->sec;
+ now.tv_sec = (time64_t)wall_clock->sec; /* TODO: [2038 safety] wall_clock->sec uses time64_t */
now.tv_nsec = wall_clock->nsec;
rmb(); /* fetch time before checking version */
} while ((wall_clock->version & 1) || (version != wall_clock->version));
@@ -138,7 +138,7 @@ void pvclock_read_wallclock(struct pvclock_wall_clock *wall_clock,
now.tv_nsec = do_div(delta, NSEC_PER_SEC);
now.tv_sec = delta;

- set_normalized_timespec(ts, now.tv_sec, now.tv_nsec);
+ set_normalized_timespec64(ts, now.tv_sec, now.tv_nsec);
}

#ifdef CONFIG_X86_64
diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c
index 2ce064a..97dd201 100644
--- a/arch/x86/xen/time.c
+++ b/arch/x86/xen/time.c
@@ -171,18 +171,12 @@ static cycle_t xen_clocksource_get_cycles(struct clocksource *cs)

static void xen_read_wallclock(struct timespec64 *ts)
{
- struct timespec ts32;
struct shared_info *s = HYPERVISOR_shared_info;
struct pvclock_wall_clock *wall_clock = &(s->wc);
- struct pvclock_vcpu_time_info *vcpu_time;
+ struct pvclock_vcpu_time_info *vcpu_time;

vcpu_time = &get_cpu_var(xen_vcpu)->time;
- /*
- * TODO: [2038 safety] pvclock_read_wallclock() should be changed
- * to use timespec64 for 2038 safety as soon as possible.
- */
- pvclock_read_wallclock(wall_clock, vcpu_time, &ts32);
- *ts = timespec_to_timespec64(ts32);
+ pvclock_read_wallclock(wall_clock, vcpu_time, ts);
put_cpu_var(xen_vcpu);
}

--
1.7.9.5

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