kernel-packages team mailing list archive

[Serge Hallyn <1567159@xxxxxxxxxxxxxxxxxx>]

Thanks for reporting this bug. The 'kvm' package shouldn't really exist.
The bug you're referring to is in the kernel kvm code, so I'm marking it
as affecting the kernel. (If it were in the userspace qemu package, then
the 'qemu' package would be the right bug target).

** Package changed: kvm (Ubuntu) => linux (Ubuntu)

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https://bugs.launchpad.net/bugs/1567159

Title:
  Ubuntu 15.10: After hot plug vcpu, kvm_arch->use_master_clock will
  never be true.

Status in linux package in Ubuntu:
  New

Bug description:
  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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