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

Gleb Natapov
2013-05-20T10:27:45Z

On Mon, May 20, 2013 at 08:25:11PM +1000, Vadim Rozenfeld wrote:
> On Mon, 2013-05-20 at 12:25 +0300, Gleb Natapov wrote:
> > On Mon, May 20, 2013 at 10:56:22AM +0200, Paolo Bonzini wrote:
> > > In any case, this patch needs more comments and a better commit message.
> > > Microsoft docs are decent, but there are several non-obvious points in
> > > how the patches were done, and they need to be documented.
> > I wish you were right about Microsoft docs :) 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.
>
> As far as I know, you cannot fall back from iTSC to PMTimer or HPET,
> but you can fallback to reference counters.
>
What if you put 0xFFFFFFFF as a sequence? Or is this another case where
the spec is wrong.

> >
> > 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
> >
> > --
> > Gleb.
>

--
Gleb.