Instead of hunting misterious stalls/hungs all over the kernel when
overflow occurs at pvclock.c:pvclock_get_nsec_offset
u64 delta = native_read_tsc() - shadow->tsc_timestamp;
and introducing hooks when places of unexpected access found, pv_clock
should be initialized for the calling cpu if overflow condition is detected.
Signed-off-by: Igor Mammedov <imammedo@xxxxxxxxxx>
---
arch/x86/kernel/pvclock.c | 18 +++++++++++++++---
1 files changed, 15 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 42eb330..b486756 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -41,9 +41,14 @@ void pvclock_set_flags(u8 flags)
valid_flags = flags;
}
-static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
+static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow,
+ bool *overflow)
{
- u64 delta = native_read_tsc() - shadow->tsc_timestamp;
+ u64 delta;
+ u64 tsc = native_read_tsc();
+ u64 shadow_timestamp = shadow->tsc_timestamp;
+ *overflow = tsc < shadow_timestamp;
+ delta = tsc - shadow_timestamp;
return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul,
shadow->tsc_shift);
}
@@ -94,12 +99,19 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
unsigned version;
cycle_t ret, offset;
u64 last;
+ bool overflow;
do {
version = pvclock_get_time_values(&shadow, src);
barrier();
- offset = pvclock_get_nsec_offset(&shadow);
+ offset = pvclock_get_nsec_offset(&shadow, &overflow);
ret = shadow.system_timestamp + offset;
+ if (unlikely(overflow)) {
+ memset(src, 0, sizeof(*src));
+ barrier();
+ x86_cpuinit.early_percpu_clock_init();
+ continue;
+ }
barrier();
} while (version != src->version);
--
1.7.7.6
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