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Konrad Wilk reported that the new delayed calibration crashes with a divide by zero on Xen. The reason is that Xen sets the pmtimer address, but reading from it returns 0xffffff. That results in the ref_start and ref_stop value being the same, so the delta is zero which causes the divide by zero later in the calculation. The conditional (!hpet && !ref_start && !ref_stop) which sanity checks the calibration reference values doesn't really make sense. If the refs are null, but hpet is on, we still want to break out. The div by zero would be possible to trigger by chance if both reads from the hardware provided the exact same value (due to hardware wrapping). So checking if both the ref values are the same should handle if we don't have hardware (both null) or if they are the same value (either by invalid hardware, or by chance), avoiding the div by zero issue. [ tglx: Applied the same fix to native_calibrate_tsc() where this check was copied from ] Reported-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by: John Stultz <johnstul@us.ibm.com> LKML-Reference: <1295024788-15619-1-git-send-email-johnstul@us.ibm.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> |
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