[Bug 116011] New: After hot plug vcpu, kvm_arch->use_master_clock will never be true.

[bugzilla-daemon@xxxxxxxxxxxxxxxxxxx]

https://bugzilla.kernel.org/show_bug.cgi?id=116011

            Bug ID: 116011
           Summary: After hot plug vcpu, kvm_arch->use_master_clock will
                    never be true.
           Product: Virtualization
           Version: unspecified
    Kernel Version: 4.5
          Hardware: x86-64
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: normal
          Priority: P1
         Component: kvm
          Assignee: virtualization_kvm@xxxxxxxxxxxxxxxxxxxx
          Reporter: changlimin@xxxxxxx
        Regression: No

1. In function kvm_write_tsc, when tsc first matched, do
kvm->arch.nr_vcpus_matched_tsc++;

2. In function pvclock_update_vm_gtod_copy, if vcpus_matched (also with other
conditions meet), ka->use_master_clock will be true;

3. After hot plug vcpu, kvm_arch_vcpu_postcreate and Qemu will call
kvm_write_tsc for the new vcpu. Because the tsc will not match, so do
kvm->arch.nr_vcpus_matched_tsc = 0;

4. For other already existed vcpu will not call kvm_write_tsc, so will not do
kvm->arch.nr_vcpus_matched_tsc++;

5. So vcpus_matched in function pvclock_update_vm_gtod_copy will be false
forever, this cause ka->use_master_clock will never be true;

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