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SubjectRe: [PATCH] BUG in pv_clock when overflow condition is detected
On 02/13/2012 08:20 PM, Igor Mammedov wrote:
> 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);

Maybe a WARN_ON_ONCE()? Otherwise a relatively minor hypervisor bug can
kill the guest.

--
error compiling committee.c: too many arguments to function



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