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x86, paravirt: don't compute pvclock adjustments if we trust the tsc

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If the HV told us we can fully trust the TSC, skip any
correction

Signed-off-by: Glauber Costa <glommer@redhat.com>
Acked-by: Zachary Amsden <zamsden@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Glauber Costa 2010-05-11 12:17:45 -04:00 committed by Avi Kivity
parent 838815a787
commit 3a0d7256a6
4 changed files with 13 additions and 0 deletions
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5
arch/x86/include/asm/kvm_para.h
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@ -21,6 +21,11 @@
*/
#define KVM_FEATURE_CLOCKSOURCE2 3
/* The last 8 bits are used to indicate how to interpret the flags field
* in pvclock structure. If no bits are set, all flags are ignored.
*/
#define KVM_FEATURE_CLOCKSOURCE_STABLE_BIT 24
#define MSR_KVM_WALL_CLOCK 0x11
#define MSR_KVM_SYSTEM_TIME 0x12

1
arch/x86/include/asm/pvclock-abi.h
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@ -39,5 +39,6 @@ struct pvclock_wall_clock {
u32 nsec;
} __attribute__((__packed__));
#define PVCLOCK_TSC_STABLE_BIT (1 << 0)
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_PVCLOCK_ABI_H */

3
arch/x86/kernel/kvmclock.c
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@ -215,4 +215,7 @@ void __init kvmclock_init(void)
clocksource_register(&kvm_clock);
pv_info.paravirt_enabled = 1;
pv_info.name = "KVM";
if (kvm_para_has_feature(KVM_FEATURE_CLOCKSOURCE_STABLE_BIT))
pvclock_set_flags(PVCLOCK_TSC_STABLE_BIT);
}

4
arch/x86/kernel/pvclock.c
View File

@ -135,6 +135,10 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
barrier();
} while (version != src->version);
if ((valid_flags & PVCLOCK_TSC_STABLE_BIT) &&
(shadow.flags & PVCLOCK_TSC_STABLE_BIT))
return ret;
/*
* Assumption here is that last_value, a global accumulator, always goes
* forward. If we are less than that, we should not be much smaller.