Re: [PATCH] KVM: x86: Don't deliver PIC interrupts to disabled APICs - v2

[Jan Kiszka <jan.kiszka@siemens.com>]

Jan Kiszka wrote:
> Jan Kiszka wrote:
>> Avi Kivity wrote:
>>> Jan Kiszka wrote:
>>>> [ taking Sheng's comments into account ]
>>>>
>>>> The logic of kvm_apic_accept_pic_intr has a minor, practically hardly
>>>> relevant incorrectness: PIC interrupts are still delivered even if the
>>>> APIC of VPU0 (BSP) is disabled. This does not comply with the Virtual
>>>> Wire mode according to the Intel MP spec.
>>>>   
>>> This breaks Windows XP with the Standard PC HAL, so I am unapplying this
>>> patch.
>> Hmm, this points to either an APIC setup or BIOS bug. To my
>> understanding, the Standard PC HAL should not fiddle with the APIC, so
>> what the BIOS leaves behind should counts. But I think I found no traces
>> of APIC manipulation in rombios32.c.
> 
> Manipulation on UP systems. There is fiddling for SMP. But I will check
> again.

I take everything back: For yet unknown reasons Windows' standard HAL
actually decides to disable the APIC actively. Either there is a
short-path around a disabled APIC for Virtual Wire mode in Real Live
(though I fail to read this out of the spec), or Windows simply has a
bug here (MS insists on NOT supporting the Standard HAL on APIC systems
[1] - precisely the setup KVM is providing). Sheng, any comments on
this? Guess we have to live with the previous version, maybe with some
refactoring + commenting.

Jan

[1] http://support.microsoft.com/kb/309283/en
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