[Qemu-devel] Re: [PATCH] Fix timer interrupt routing for non-ACPI guest

["Sebastian Herbszt" <herbszt@gmx.de>]

Ed Swierk wrote:
> Qemu 0.10.2 is unable to boot a non-ACPI kernel due to a BIOS bug:
> 
> ENABLING IO-APIC IRQs 
> ..TIMER: vector=0x31 apic1=0 pin1=0 apic2=-1 pin2=-1 
> ..MP-BIOS bug: 8254 timer not connected to IO-APIC 
> ...trying to set up timer (IRQ0) through the 8259A ... 
> ..... (found apic 0 pin 0) ... 
> ....... failed. 
> ...trying to set up timer as Virtual Wire IRQ... 

I tried Linux 2.6.27.7 and it seems to hang after
"...trying to set up timer as Virtual Wire IRQ...".

On 2.6.25.5 it managed to use Virtual Wire mode:

..TIMER: vector=0x31 apic1=0 pin1=0 apic2=-1 pin2=-1
..MP-BIOS bug: 8254 timer not connected to IO-APIC
...trying to set up timer (IRQ0) through the 8259A ...  failed.
...trying to set up timer as Virtual Wire IRQ... works.
testing the IO APIC.......................
.................................... done.

> The interrupt routing table in the MPTABLE needs to route the timer
> interrupt (IRQ 0) to IOAPIC pin 2.

Do you refer here to "5.3 Assigning of I/O Interrupts to the APIC I/O Unit"
from MultiProcessor Specification 1.4 or some other documentation?

> A similar bug was recently fixed in the ACPI table code. 

Can you point me to the patch?

> This patch fixes the problem for non-ACPI guests.

Linux displays the following without any patch:

Int: type 0, pol 0, trig 0, bus 00, IRQ 00, APIC ID 1, APIC INT 00
Int: type 0, pol 0, trig 0, bus 00, IRQ 01, APIC ID 1, APIC INT 01
Int: type 0, pol 0, trig 0, bus 00, IRQ 02, APIC ID 1, APIC INT 02
Int: type 0, pol 0, trig 0, bus 00, IRQ 03, APIC ID 1, APIC INT 03
...
..TIMER: vector=0x31 apic1=0 pin1=0 apic2=-1 pin2=-1

[older Linux output]
IRQ to pin mappings:
IRQ0 -> 0:0
IRQ1 -> 0:1
IRQ2 -> 0:2
IRQ3 -> 0:3

With your patch it's:

Int: type 0, pol 0, trig 0, bus 00, IRQ 00, APIC ID 1, APIC INT 00
Int: type 0, pol 0, trig 0, bus 00, IRQ 01, APIC ID 1, APIC INT 01
Int: type 0, pol 0, trig 0, bus 00, IRQ 00, APIC ID 1, APIC INT 02
Int: type 0, pol 0, trig 0, bus 00, IRQ 03, APIC ID 1, APIC INT 03
...
..TIMER: vector=0x31 apic1=0 pin1=0 apic2=-1 pin2=-1

[older Linux output]
IRQ to pin mappings:
IRQ0 -> 0:0-> 0:2
IRQ1 -> 0:1
IRQ3 -> 0:3

Is this mapping correct or should it rather be the following?

..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1

IRQ0 -> 0:2
IRQ1 -> 0:1
IRQ3 -> 0:3

- Sebastian