Re: [Xen-devel] Bug: Windows 2003 fails to install on xen-unstable tip

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.13 at 12:38, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 23/04/13 11:25, Jan Beulich wrote:
>> Just to double check - could you comment out entirely the first
>> (normal code, i.e. not the one marked //todo?) "else if" in
>> rtc_periodic_interrupt() (including its body of course)? I would
>> expect this to not make a difference, and if so I don't see how
>> Windows expects to be woken up again (I would guess that
>> they internally have some gating logic preventing the normal IRQ8
>> handling to happen, yet of course we don't know what would
>> reset that state).
> 
> In fact, when I comment out that region, then it hangs in the guest BIOS 
> before even attempting to boot the CD.

That's due to a different issue, that I meanwhile found a fix for
(caused by the general vpt code expecting interrupts to be
delivered, yet the BIOS doesn't enable the interrupt, and hence
the RTC periodic timer doesn't get advanced to the next tick,
and it having an earlier expiration time than the PIT one prevents
pt_update_irq() to pick that one up for processing).

With that fixed and the mentioned code block removed, things
work as I had expected. But the logging that I added in the
course of all this shows that it really juts happens to work,
I can't really explain why (other than the myriads of superfluous
interrupts attempted to be injected into the guest keeping the
VM alive). In particular, almost none of the injected IRQs
actually reach their handler (there are only very few REG_C
reads), but the handler also doesn't do anything really
interesting (i.e. we don't actually need the handler to execute,
we just need to keep a flow of interrupts going into the VM).
Yet I did verify that the correct values get actually written
through vmx_inject_extint()/__vmx_inject_exception().

So at this point I'm of the opinion that the RTC changes really
just exposed a completely different issue, and I'm of the opinion
that this is what needs fixing, not papering over it by reverting
the RTC stuff.

Jan


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