Re: [Xen-devel] [PATCH] Re: Ever increasing time offset for HVM domain / Huge amounts of drift

[Tim Deegan <tim@xxxxxxx>]

At 17:02 +0000 on 17 Jan (1358442159), Jan Beulich wrote:
> >>> On 17.01.13 at 17:41, Tim Deegan <tim@xxxxxxx> wrote:
> > At 13:55 +0000 on 17 Jan (1358430927), Tim Deegan wrote:
> >> It's possible that the code to calculate 'current CMOS time' for a VM is
> >> buggy -- that was changed in 4.2.  Cc'ing the people who touched that
> >> code in 4.2 for their opinions.
> > 
> > In fact I think it's the code that handles CMOS writes.  The attached
> > patch fixes the issue for me; can you try it on your system?
> 
> Looks plausible, so feel free to put my ack on it if it also helps
> Phil.
> 
> > (Jan, this is a candidate for applying to 4.2 as well as unstable.)
> 
> I agree, but the code you touch here hasn't been changed for
> years (and even the involved helper functions changed only
> marginally between 4.1 and 4.2), so wouldn't that have been
> a problem for much longer? In which case it ought to also go
> into 4.1?

The bug was introduced in 24974:6deb0b626f3f, when the 1-second timer
that used to keep those registers up-to-date was removed; AFAICT that's
only in 4.2.

Tim.

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