KVM: x86: Robust TSC compensation
Make the match of TSC find TSC writes that are close to each other instead of perfectly identical; this allows the compensator to also work in migration / suspend scenarios. Signed-off-by: Zachary Amsden <zamsden@redhat.com> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
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@ -928,21 +928,27 @@ void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
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struct kvm *kvm = vcpu->kvm;
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struct kvm *kvm = vcpu->kvm;
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u64 offset, ns, elapsed;
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u64 offset, ns, elapsed;
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unsigned long flags;
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unsigned long flags;
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s64 sdiff;
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spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
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spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
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offset = data - native_read_tsc();
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offset = data - native_read_tsc();
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ns = get_kernel_ns();
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ns = get_kernel_ns();
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elapsed = ns - kvm->arch.last_tsc_nsec;
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elapsed = ns - kvm->arch.last_tsc_nsec;
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sdiff = data - kvm->arch.last_tsc_write;
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if (sdiff < 0)
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sdiff = -sdiff;
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/*
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/*
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* Special case: identical write to TSC within 5 seconds of
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* Special case: close write to TSC within 5 seconds of
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* another CPU is interpreted as an attempt to synchronize
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* another CPU is interpreted as an attempt to synchronize
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* (the 5 seconds is to accomodate host load / swapping).
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* The 5 seconds is to accomodate host load / swapping as
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* well as any reset of TSC during the boot process.
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*
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*
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* In that case, for a reliable TSC, we can match TSC offsets,
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* In that case, for a reliable TSC, we can match TSC offsets,
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* or make a best guest using kernel_ns value.
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* or make a best guest using elapsed value.
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*/
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*/
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if (data == kvm->arch.last_tsc_write && elapsed < 5ULL * NSEC_PER_SEC) {
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if (sdiff < nsec_to_cycles(5ULL * NSEC_PER_SEC) &&
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elapsed < 5ULL * NSEC_PER_SEC) {
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if (!check_tsc_unstable()) {
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if (!check_tsc_unstable()) {
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offset = kvm->arch.last_tsc_offset;
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offset = kvm->arch.last_tsc_offset;
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pr_debug("kvm: matched tsc offset for %llu\n", data);
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pr_debug("kvm: matched tsc offset for %llu\n", data);
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