← Back to team overview

kernel-packages team mailing list archive

[Bug 1567159] Re: Ubuntu 15.10: After hot plug vcpu, kvm_arch->use_master_clock will never be true.

 

No pending crash reports. 
The influence is: After hot plug vcpu, kvm_arch->use_master_clock will never be true, even if use_master_clock is true before hot plug vcpu.

** Changed in: linux (Ubuntu)
       Status: Incomplete => Confirmed

-- 
You received this bug notification because you are a member of Kernel
Packages, which is subscribed to linux in Ubuntu.
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:
  Confirmed

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;

To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1567159/+subscriptions