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Commit 3a0d7256 authored by Glauber Costa's avatar Glauber Costa Committed by Avi Kivity
Browse files

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



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

Signed-off-by: default avatarGlauber Costa <glommer@redhat.com>
Acked-by: default avatarZachary Amsden <zamsden@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
parent 838815a7

arch/x86/include/asm/kvm_para.h

+5 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/include/asm/pvclock-abi.h

+1 −0
Original line number Diff line number Diff line
@@ -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 */

arch/x86/kernel/kvmclock.c

+3 −0
Original line number Diff line number Diff line
@@ -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);

}

arch/x86/kernel/pvclock.c

+4 −0
Original line number Diff line number Diff line
@@ -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.