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charset="utf-8" Looping until reaching/exceeding a certain value is error prone: If the target value is close enough to the wrapping point, the loop may not terminate at all. Switch to using delta values, which then allows to fold the two loops each into just one. Fixes: 93340297802b ("x86/time: calibrate TSC against platform timer") Reported-by: Roger Pau Monn=C3=A9 Signed-off-by: Jan Beulich Reviewed-by: Roger Pau Monn=C3=A9 --- a/xen/arch/x86/time.c +++ b/xen/arch/x86/time.c @@ -378,7 +378,7 @@ static u64 read_hpet_count(void) static int64_t __init init_hpet(struct platform_timesource *pts) { uint64_t hpet_rate, start; - uint32_t count, target; + uint32_t count, target, elapsed; /* * Allow HPET to be setup, but report a frequency of 0 so it's not sel= ected * as a timer source. This is required so it can be used in legacy @@ -451,11 +451,8 @@ static int64_t __init init_hpet(struct p =20 count =3D hpet_read32(HPET_COUNTER); start =3D rdtsc_ordered(); - target =3D count + CALIBRATE_VALUE(hpet_rate); - if ( target < count ) - while ( hpet_read32(HPET_COUNTER) >=3D count ) - continue; - while ( hpet_read32(HPET_COUNTER) < target ) + target =3D CALIBRATE_VALUE(hpet_rate); + while ( (elapsed =3D hpet_read32(HPET_COUNTER) - count) < target ) continue; =20 return (rdtsc_ordered() - start) * CALIBRATE_FRAC; @@ -493,8 +490,8 @@ static u64 read_pmtimer_count(void) =20 static s64 __init init_pmtimer(struct platform_timesource *pts) { - u64 start; - u32 count, target, mask; + uint64_t start; + uint32_t count, target, mask, elapsed; =20 if ( !pmtmr_ioport || (pmtmr_width !=3D 24 && pmtmr_width !=3D 32) ) return 0; @@ -504,11 +501,8 @@ static s64 __init init_pmtimer(struct pl =20 count =3D inl(pmtmr_ioport) & mask; start =3D rdtsc_ordered(); - target =3D count + CALIBRATE_VALUE(ACPI_PM_FREQUENCY); - if ( target < count ) - while ( (inl(pmtmr_ioport) & mask) >=3D count ) - continue; - while ( (inl(pmtmr_ioport) & mask) < target ) + target =3D CALIBRATE_VALUE(ACPI_PM_FREQUENCY); + while ( (elapsed =3D (inl(pmtmr_ioport) & mask) - count) < target ) continue; =20 return (rdtsc_ordered() - start) * CALIBRATE_FRAC;