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[Bug 1567167] [NEW] Ubuntu 15.10: tsc_offset is error for hot-plugged vcpu.

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From: Launchpad Bug Tracker <1567167@xxxxxxxxxxxxxxxxxx>
Date: Thu, 07 Apr 2016 17:10:52 -0000
Reply-to: Bug 1567167 <1567167@xxxxxxxxxxxxxxxxxx>
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You have been subscribed to a public bug:

1. when hot plug vcpu, KVM will call kvm_write_tsc set the new vcpu's
tsc_offset to host tsc.  The new vcpu's tsc_offsets is greatly different
from preallocated vcpu's tsc_offset.

2. For redhat 6.x, the vm will show warning and turn off TSC clock.
kernel: CPU 1 got hotplugged
kernel: kvm-clock: cpu 1, msr 0:282367c1, secondary cpu clock
kernel: TSC synchronization [CPU#0 -> CPU#1]:
kernel: Measured 150076598781 cycles TSC warp between CPUs, turning off TSC clock.
kernel: Marking TSC unstable due to check_tsc_sync_source failed

3. I think should set the new vcpu's tsc_offset to
kvm->arch.cur_tsc_offset.

** Affects: linux (Ubuntu)
     Importance: Undecided
         Status: New

-- 
Ubuntu 15.10: tsc_offset is error for hot-plugged vcpu.
https://bugs.launchpad.net/bugs/1567167
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