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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 23.04.13 at 16:57, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
> On 23/04/13 15:55, Jan Beulich wrote:
>>>>> On 23.04.13 at 16:21, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
>>> On 23/04/13 14:00, Jan Beulich wrote:
>>>>>>> On 23.04.13 at 13:52, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:
>>>>> On 23/04/13 12:33, Jan Beulich wrote:
>>>> Just went through that change again: The only thing that changes
>>>> is that while rtc_periodic_cb() (simply setting REG_C flags) got
>>>> called at the end of pt_intr_post(), rtc_periodic_interrupt() now
>>>> gets called from pt_update_irq(), and therefore takes care of
>>>> asserting the IRQ itself (which originally happened inside
>>>> pt_update_irq()) along with setting REG_C flags. Bottom line -
>>>> all the patch changes is when exactly REG_PF (and possibly
>>>> REG_IRQF) get set, and whether the IRQ actually gets asserted.
>>> So that last bit seems to do these things:
>>> a. Changes when the handling happens in the Xen interrupt handler
>>> b. Causes assert/deassert to only happen if !(C.PF) && (B.PIE)
>>>     (Before it happened unconditionally)
>>> c. Causes C.IRQF=1 only if (same condition above)
>>>    (Before it happened unconditionally)
>>> d. Runs destroy_periodic_timer() if C.PF already
>>>
>>> So just to figure out what it was that w2k3 wanted, I tried a bunch of
>>> variations:
>>>
>>> * All of above
>>>    BAD
>>> * a only; always assert/deassert + set C.IRQF
>>>    GOOD
>>> * always assert/deassert, but leave destroy_periodic_timer and IRQF
>>> setting alone
>>>    FAIL
>>> * destroy if C.PF, assert/deassert, set IRQF if setting C.PF (don't
>>> check B.PIE)
>>>    FAIL
>>> * destroy if C.PF, always assert/deassert + set C.IRQF
>>>    FAIL
>>> * never destroy, assert/deassert + set C.IRQF if setting C.PF
>>>    FAIL
>>> * never destroy, assert/deassert + set C.IRQF if !C.IRQF
>>>    FAIL
>>>
>>> In short, it seems that w2k3 basically expects an unlimited number of
>>> attempts to actually deliver the interrupt.
>> Not always doing the deassert/assert pair was actually part of Tim's
>> subsequent changes - before that it got called conditionally upon
>> B.PIE, but always set C.IRQF and always deasserted and asserted.
>> Since we know from the debug log that B.PIE is set, I fail to see how
>> the code prior to "x86/hvm: Centralize and simplify the RTC IRQ logic"
>> would have not worked, but the above case turned out GOOD.
>>
>> So did his earlier 3 changes perhaps fix the issue, and the fourth re-
>> introduced it?
> 
> If you've got a git hash I can try to revert it.

527824f41f5fac9cba3d4441b2e73d3118d98837

Jan


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