Messages in this thread |  | | | Date | Sun, 15 Mar 2009 15:56:52 -0400 | | Subject | Re: [Patch] Fix the possibility of insane return value of hpet_calibrate() against SMI. | | From | Paul Gortmaker <> |
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On Fri, Mar 13, 2009 at 1:00 AM, Yasunori Goto <y-goto@jp.fujitsu.com> wrote: > Hello. > > I think there is a possibility that HPET driver will return > insane value due to a SMI interruption (or switching guests by hypervisor). > I found it by reviewing, and I would like to fix it. > > Current HPET driver calibrates the adjustment value > by calculation the elapse time in CPU busy loop. > However this way is too dangerous against SMI interruption. > > Here is the calibration code in hpet_calibrate() > > 701 static unsigned long hpet_calibrate(struct hpets *hpetp) > : > : > 728 do { > 729 m = read_counter(&hpet->hpet_mc); > 730 write_counter(t + m + hpetp->hp_delta, &timer->hpet_compare); > 731 } while (i++, (m - start) < count); > 732 > 733 local_irq_restore(flags); > 734 > 735 return (m - start) / i; > > If SMI interruption occurs between 728 to 731, then return value will be > bigger value than correct one. (SMI is not able to be controlled by OS.) > > > This patch is a simple solution to fix it. > hpet_calibrate() is called 5 times, and one of them is expected as > correct value.
I've no sense of feel for how long each calibration run would take. Would doing it 5 times show up as a significant increase in the boot time for those that care about boot time being as quick as possible?
Paul.
> > Thanks. > > > --- > > hpet_calibrate() has a possibility of miss-calibration due to SMI. > If SMI interrupts in the while loop of calibration, then return value > will be big. This changes it tries 5 times and get minimum value as > correct value. > > Signed-off-by: Yasunori Goto <y-goto@jp.fujitsu.com> > > --- > > Index: hpet_test/drivers/char/hpet.c > =================================================================== > --- hpet_test.orig/drivers/char/hpet.c 2008-12-04 16:24:02.000000000 +0900 > +++ hpet_test/drivers/char/hpet.c 2008-12-04 16:34:59.000000000 +0900 > @@ -713,7 +713,7 @@ > */ > #define TICK_CALIBRATE (1000UL) > > -static unsigned long hpet_calibrate(struct hpets *hpetp) > +static unsigned long __hpet_calibrate(struct hpets *hpetp) > { > struct hpet_timer __iomem *timer = NULL; > unsigned long t, m, count, i, flags, start; > @@ -750,6 +750,17 @@ > return (m - start) / i; > } > > +static unsigned long hpet_calibrate(struct hpets *hpetp) > +{ > + unsigned long ret = ~0UL, i; > + > + /* Try 5 times to remove impact of SMI.*/ > + for (i = 0; i < 5; i++) > + ret = min(ret, __hpet_calibrate(hpetp)); > + > + return ret; > +} > + > int hpet_alloc(struct hpet_data *hdp) > { > u64 cap, mcfg; > > -- > Yasunori Goto > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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