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Subject[PATCH] X86_64: hpet tsc calibration fix broken smi detection logic
The current SMI detection logic in read_hpet_tsc() makes sure,
that when a SMI happens between the read of the HPET counter and
the read of the TSC, this wrong value is used for TSC calibration.

This is not the intention of the function. The comparison must ensure,
that we do _NOT_ use such a value.

Fix the check to use calibration values where delta of the two TSC reads
is smaller than a reasonable threshold.

Signed-off-by: Thomas Gleixner <>

--- a/arch/x86_64/kernel/hpet.c
+++ b/arch/x86_64/kernel/hpet.c
@@ -190,7 +190,7 @@ int hpet_reenable(void)

#define TICK_COUNT 100000000
-#define TICK_MIN 5000
+#define SMI_THRESHOLD 50000
#define MAX_TRIES 5

@@ -205,7 +205,7 @@ static void __init read_hpet_tsc(int *hpet, int *tsc)
tsc1 = get_cycles_sync();
hpet1 = hpet_readl(HPET_COUNTER);
tsc2 = get_cycles_sync();
- if (tsc2 - tsc1 > TICK_MIN)
+ if ((tsc2 - tsc1) < SMI_TRESHOLD)
*hpet = hpet1;

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