Re: [PATCH kvm-unit-tests] KVM: x86: add hyperv clock test case

[Paolo Bonzini <pbonzini@redhat.com>]

On 04/02/2016 10:33, Roman Kagan wrote:
>> The bit that I was missing last week was how the guest could perceive
>> updates to the TSC page parameters as atomic.  We actually _can_
>> emulate seqlock-like behavior in Hyper-V by writing 0 to seq during
>> an update.  Instead of looping like seqlocks do, the guest will simply
>> use the time reference counter and take a hypervisor exit.  The result
>> however is still valid, because we want the time reference counter to
>> be perfectly synchronized with the Hyper-V clock and lets you handle
>> any kvmclock update scenario safely.
> 
> That's smart, thanks for the idea!  We'll only need to check that
> Windows goes through all these steps on every clock read, rather than
> remembering the failure and sticking with the MSR for good.

Andrey pointed me to https://lkml.org/lkml/2015/11/2/655, which has the
source for Windows's clock read code.  It should work.

>> The remaining part is _further_ adjusting the offset to
> 
> ...?

Cut and paste. :)  I'll take a look at it if it's not super-high
priority for you.

Paolo