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

Gleb Natapov
2013-05-20T09:25:23Z

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.

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.