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

[Sebastian Herbszt]

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


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[Sebastian Herbszt]

Ed Swierk wrote:

>>> 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?
>
> I confess I haven't checked actual documentation; instead I've
> referred to code from Coreboot that seems to work. For example the
> bus_isa interrupts at
> http://tracker.coreboot.org/trac/coreboot/browser/trunk/coreboot-v2/src/mainboard/msi/ms9185/mptable.c
> .

Looks like this sets:

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

This seems to also be what VMware provides:

Int: type 3, pol 1, trig 1, bus 02, IRQ 00, APIC ID 1, APIC INT 00
Int: type 0, pol 1, trig 1, bus 02, IRQ 01, APIC ID 1, APIC INT 01
Int: type 0, pol 1, trig 1, bus 02, IRQ 00, APIC ID 1, APIC INT 02
Int: type 0, pol 1, trig 1, bus 02, IRQ 03, APIC ID 1, APIC INT 03
..TIMER: vector=0x31 apic1=0 pin1=2 apic2=0 pin2=0
 
>> ..TIMER: vector=0x31 apic1=0 pin1=2 apic2=-1 pin2=-1
>>
>> IRQ0 -> 0:2
>> IRQ1 -> 0:1
>> IRQ3 -> 0:3
>
> I suspect the latter is correct but I don't know that it really makes
> a difference, at least to Linux.

We can achieve this

Int: type 3, pol 0, trig 0, bus 00, IRQ 00, APIC ID 1, APIC INT 00
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 01, APIC ID 1, APIC INT 01
Int: type 0, pol 0, trig 0, bus 00, IRQ 03, APIC ID 1, APIC INT 03
..TIMER: vector=0x31 apic1=0 pin1=2 apic2=0 pin2=0

with the following patch.

- Sebastian

Index: bochs-cvs/bios/rombios32.c
===================================================================
--- bochs-cvs.orig/bios/rombios32.c
+++ bochs-cvs/bios/rombios32.c
@@ -1142,16 +1142,27 @@ static void mptable_init(void)
     putb(&q, 1); /* enable */
     putle32(&q, 0xfec00000); /* I/O APIC addr */

+    putb(&q, 3); /* entry type = I/O interrupt */
+    putb(&q, 3); /* interrupt type = ExtINT */
+    putb(&q, 0); /* flags: po=0, el=0 */
+    putb(&q, 0);
+    putb(&q, 0); /* source bus ID = ISA */
+    putb(&q, 0); /* source bus IRQ */
+    putb(&q, ioapic_id); /* dest I/O APIC ID */
+    putb(&q, 0); /* dest I/O APIC interrupt in */
+
     /* irqs */
     for(i = 0; i < 16; i++) {
+        if (i == 2)
+            continue;
         putb(&q, 3); /* entry type = I/O interrupt */
         putb(&q, 0); /* interrupt type = vectored interrupt */
         putb(&q, 0); /* flags: po=0, el=0 */
         putb(&q, 0);
         putb(&q, 0); /* source bus ID = ISA */
-        putb(&q, (i == 2) ? 0 : i); /* source bus IRQ */
+        putb(&q, i); /* source bus IRQ */
         putb(&q, ioapic_id); /* dest I/O APIC ID */
-        putb(&q, i); /* dest I/O APIC interrupt in */
+        putb(&q, (i == 0) ? 2 : i); /* dest I/O APIC interrupt in */
     }
     /* patch length */
     len = q - mp_config_table;


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