[Qemu-devel] Re: PATCH: debugging apic

[Jan Kiszka]

Am 28.09.2010 21:57, Sam King wrote:
>  Thanks to Bernhard Kauer for pointing out the problem.  Apparently if
> software disables LVT_LINT0 when there is a pending CPU_HARD_INTERRUPT
> you can get into trouble.  I attached a patch that fixes the problem by
> resetting the interrupt_request.  I am not sure if we need to do the
> same for LINT1, but this fixed the incorrect GPF I was getting.
> 

...
[ please inline patches ]

> *** hw/apic.c 2010-07-22 07:39:04.000000000 -0500
> --- ../qemu-0.12.5-fixed/hw/apic.c    2010-09-28 14:45:55.476945540 -0500
> ***************
> *** 841,846 ****
> --- 841,851 ----
>               s->lvt[n] = val;
>               if (n == APIC_LVT_TIMER)
>                   apic_timer_update(s, qemu_get_clock(vm_clock));
> + 
> +             if(n == APIC_LVT_LINT0) {
> +                 if((val & APIC_LVT_MASKED) && (env->interrupt_request & 
> CPU_INTERRUPT_HARD))
> +                     cpu_reset_interrupt(env, CPU_INTERRUPT_HARD);
> +             }
>           }
>           break;
>       case 0x38:

This actually points out open issues, but more work is required:

You need to consider other potentially pending interrupts as well, thus
you must not blindly reset here. And the same is true for invocations of
apic_deliver_pic_intr(..., 0). The APIC has to save the PIC line state
and forward it according to its current LVT mask state, which includes
raising the interrupt if the mask is removed while the PIC line is high.

Jan

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