Re: RFC: VMX: initialize TSC offset relative to vm creation time

[Avi Kivity <avi@qumranet.com>]

Marcelo Tosatti wrote:
> VMX initializes the TSC offset for each vcpu at different times, and
> also reinitializes it for vcpus other than 0 on APIC SIPI message.
>
> This bug causes the TSC's to appear unsynchronized in the guest, even if
> the host is good.
>
> Older Linux kernels don't handle the situation very well, so
> gettimeofday is likely to go backwards in time:
>
> http://www.mail-archive.com/kvm@vger.kernel.org/msg02955.html
> http://sourceforge.net/tracker/index.php?func=detail&aid=2025534&group_id=180599&atid=893831
>
> Fix it by initializating the offset of each vcpu relative to vm creation
> time, and moving it from vmx_vcpu_reset to vmx_vcpu_setup, out of the
> APIC MP init path.
>
>
>   

This is good in principle, but we need to detect if we're on a multiple
board host (or a host with unsynced tscs) and do something else in that
case.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.