If the HV told us we can fully trust the TSC, skip any
correction
Signed-off-by: Glauber Costa <glommer@xxxxxxxxxx>
---
arch/x86/include/asm/kvm_para.h | 5 +++++
arch/x86/include/asm/pvclock-abi.h | 1 +
arch/x86/kernel/kvmclock.c | 3 +++
arch/x86/kernel/pvclock.c | 4 ++++
4 files changed, 13 insertions(+), 0 deletions(-)
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index f019f8c..6f1b878 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -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_TSC 24
+
#define MSR_KVM_WALL_CLOCK 0x11
#define MSR_KVM_SYSTEM_TIME 0x12
diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include/asm/pvclock-abi.h
index ec5c41a..b123bd7 100644
--- a/arch/x86/include/asm/pvclock-abi.h
+++ b/arch/x86/include/asm/pvclock-abi.h
@@ -39,5 +39,6 @@ struct pvclock_wall_clock {
u32 nsec;
} __attribute__((__packed__));
+#define PVCLOCK_STABLE_TSC (1 << 0)
#endif /* __ASSEMBLY__ */
#endif /* _ASM_X86_PVCLOCK_ABI_H */
diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
index 59c740f..518de01 100644
--- a/arch/x86/kernel/kvmclock.c
+++ b/arch/x86/kernel/kvmclock.c
@@ -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_TSC))
+ pvclock_set_flags(PVCLOCK_STABLE_TSC);
}
diff --git a/arch/x86/kernel/pvclock.c b/arch/x86/kernel/pvclock.c
index 3dff5fa..0d4fe0c 100644
--- a/arch/x86/kernel/pvclock.c
+++ b/arch/x86/kernel/pvclock.c
@@ -135,6 +135,10 @@ cycle_t pvclock_clocksource_read(struct pvclock_vcpu_time_info *src)
barrier();
} while (version != src->version);
+ if ((valid_flags & PVCLOCK_STABLE_TSC) &&
+ (shadow.flags & PVCLOCK_STABLE_TSC))
+ 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.
--
1.6.2.2
--
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