Re: [RFC PATCH 1/2] Hyper-H reference counter

Paolo Bonzini
2013-05-20T09:32:35Z

Il 20/05/2013 11:25, Gleb Natapov ha scritto:
> So in Hyper-V spec they
> say:
>
> Special value of 0xFFFFFFFF is used to indicate that this facility is no
> longer a reliable source of reference time and the virtual machine must
> fall back to a different source (for example, the virtual PM timer).
>
> May be they really mean "virtual PM timer" here and reference counter is
> not considered as a fall back source, but this is not what we want.
>
> On the other hand in API specification [1] they have:
>
> #define HV_REFERENCE_TSC_SEQUENCE_INVALID (0x00000000)
>
> which is not even documented in hyper-v spec. Actually 0 is specified as
> valid value there. Go figure.
>
> [1] http://msdn.microsoft.com/en-us/library/windows/hardware/ff540244%28v=vs.85%29.aspx

Ok, if the API document is right then we should use
HV_REFERENCE_TSC_SEQUENCE_INVALID instead of 0, with a comment
explaining why we use 0 and not 0xFFFFFFFF.

Paolo