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Date: Tue, 17 Jun 2008 09:58:54 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: [Qemu-devel] Re: loadvm and APIC
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To: qemu-devel@nongnu.org

malc wrote:
> Here's the scenario:
> 
> 1. Start QEMU and boot Linux capable of using APIC
> 2. Save the VM state
> 3. Exit QEMU
> 4. Start QEMU and loadvm
> 
> Kernel instantly panics. Here's why:
> 
> Upon starting eventually following happens:
> ... -> pc_init -> ... -> pit_irq_timer_update
>   -> qemu_set_irq -> ...
>     -> apic_local_deliver -> cpu_interrupt(CPU_INTERRUPT_HARD)
> 
> Then qemu_loadvm_state begins executing load handlers eventually coming
> to apic_load which loads the state from the storage overriding all the
> effects of apic_local_deliver, in the meantime env->interrupt_request
> stays the same.
> 
> Then cpu_exec is entered and it arrives at line 399 where
> cpu_get_pic_interrupt calls apic_get_interrupt which returns -1, this
> bogus interrupt number is then passed to do_interrupt and here it is
> finally caught by a IDT limit check at line 649, general protection
> fault is generated and kernel inside the VM panics.
> 
> Hence:
> 
> diff --git a/vl.c b/vl.c
> index d759fde..11827ba 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -6296,6 +6296,7 @@ void do_loadvm(const char *name)
>          goto the_end;
>      }
>      ret = qemu_loadvm_state(f);
> +    first_cpu->interrupt_request = 0;
>      qemu_fclose(f);
>      if (ret < 0) {
>          term_printf("Error %d while loading VM state\n", ret);
> 
> Okay to commit?

That is basically
http://permalink.gmane.org/gmane.comp.emulators.qemu/26215, which I
would prefer.

Jan

-- 
Siemens AG, Corporate Technology, CT SE 2
Corporate Competence Center Embedded Linux