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Subject[PATCH] BUG in pv_clock when overflow condition is detected
Date
BUG when overflow occurs at pvclock.c:pvclock_get_nsec_offset

u64 delta = native_read_tsc() - shadow->tsc_timestamp;

this might happen at an attempt to read an uninitialized yet clock.
It won't prevent stalls and hangs but at least it won't do it silently.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
arch/x86/kernel/pvclock.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 42eb330..35a6190 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -43,7 +43,10 @@ void pvclock_set_flags(u8 flags)

static u64 pvclock_get_nsec_offset(struct pvclock_shadow_time *shadow)
{
- u64 delta = native_read_tsc() - shadow->tsc_timestamp;
+ u64 delta;
+ u64 tsc = native_read_tsc();
+ BUG_ON(tsc < shadow->tsc_timestamp);
+ delta = tsc - shadow->tsc_timestamp;
return pvclock_scale_delta(delta, shadow->tsc_to_nsec_mul,
shadow->tsc_shift);
}
--
1.7.7.6


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