> -----Original Message----- > From: Wei Liu <w...@xen.org> > Sent: 18 December 2019 22:21 > To: Michael Kelley <mikel...@microsoft.com> > Cc: Durrant, Paul <pdurr...@amazon.com>; Wei Liu <w...@xen.org>; Xen > Development List <xen-devel@lists.xenproject.org>; Wei Liu > <li...@microsoft.com>; Jan Beulich <jbeul...@suse.com>; Andrew Cooper > <andrew.coop...@citrix.com>; Roger Pau Monné <roger....@citrix.com> > Subject: Re: [PATCH v2 6/6] x86: implement Hyper-V clock source > > On Wed, 18 Dec 2019 at 20:24, Michael Kelley <mikel...@microsoft.com> > wrote: > > > > From: Durrant, Paul <pdurr...@amazon.com> Sent: Wednesday, December 18, > 2019 7:24 AM > > > > > > From: Wei Liu <wei.liu....@gmail.com> On Behalf Of Wei Liu > > > > Sent: 18 December 2019 14:43 > > > > [snip] > > > > > > + > > > > +static inline uint64_t read_hyperv_timer(void) > > > > +{ > > > > + uint64_t scale, offset, ret, tsc; > > > > + uint32_t seq; > > > > + const struct ms_hyperv_tsc_page *tsc_page = hyperv_tsc; > > > > + > > > > + do { > > > > + seq = tsc_page->tsc_sequence; > > > > + > > > > + /* Seq 0 is special. It means the TSC enlightenment is not > > > > + * available at the moment. The reference time can only be > > > > + * obtained from the Reference Counter MSR. > > > > + */ > > > > + if ( seq == 0 ) > > > > > > Older versions of the spec used to use 0xFFFFFFFF I think, although > when I look again they > > > seem to have been retro-actively fixed. In any case I think you should > treat both > > > 0xFFFFFFFF and 0 as invalid. > > > > FWIW, the 0xFFFFFFFF was just a bug in the spec. Hyper-V > implementations only > > set the value to 0 to indicate invalid. The equivalent Linux code > checks only for 0. > > > > Thanks for chiming in, Michael. > > In that case I will submit a fix to change Xen's viridian code to > remove the wrong value there.
If no consuming version of Windows is going to be upset seeing all-Fs then that's fine. Thanks for the clarification. Cheers, Paul _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel