Re: [Qemu-devel] Re: Errors on MMIO read access on VM suspend / resume operations

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

On 01/26/2011 03:14 AM, Jan Kiszka wrote:
> On 2011-01-25 17:49, Stefan Berger wrote:
>> On 01/25/2011 02:26 AM, Jan Kiszka wrote:
>>> Do you see a chance to look closer at the issue yourself? E.g.
>>> instrument the kernel's irqchip models and dump their states once your
>>> guest is stuck?
>> The device runs on iRQ 3. So I applied this patch here.
>>
>> diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
>> index 3cece05..8f4f94c 100644
>> --- a/arch/x86/kvm/i8259.c
>> +++ b/arch/x86/kvm/i8259.c
>> @@ -106,7 +106,7 @@ static inline int pic_set_irq1(struct kvm_kpic_state
>> *s, int irq, int level)
>>   {
>>       int mask, ret = 1;
>>       mask = 1<<   irq;
>> -    if (s->elcr&   mask)    /* level triggered */
>> +    if (s->elcr&   mask)    /* level triggered */ {
>>           if (level) {
>>               ret = !(s->irr&   mask);
>>               s->irr |= mask;
>> @@ -115,7 +115,10 @@ static inline int pic_set_irq1(struct
>> kvm_kpic_state *s, int irq, int level)
>>               s->irr&= ~mask;
>>               s->last_irr&= ~mask;
>>           }
>> -    else    /* edge triggered */
>> +if (irq == 3)
>> +    printk("%s %d: level=%d, irr = %x\n", __FUNCTION__,__LINE__,level,
>> s->irr);
>> +        }
>> +    else    /* edge triggered */ {
>>           if (level) {
>>               if ((s->last_irr&   mask) == 0) {
>>                   ret = !(s->irr&   mask);
>> @@ -124,7 +127,9 @@ static inline int pic_set_irq1(struct kvm_kpic_state
>> *s, int irq, int level)
>>               s->last_irr |= mask;
>>           } else
>>               s->last_irr&= ~mask;
>> -
>> +if (irq == 3)
>> +    printk("%s %d: level=%d, irr = %x\n", __FUNCTION__,__LINE__,level,
>> s->irr);
>> +        }
>>       return (s->imr&   mask) ? -1 : ret;
>>   }
>>
>> @@ -206,6 +211,8 @@ int kvm_pic_set_irq(void *opaque, int irq, int level)
>>
>>       pic_lock(s);
>>       if (irq>= 0&&   irq<   PIC_NUM_PINS) {
>> +if (irq == 3)
>> +printk("%s\n", __FUNCTION__);
>>           ret = pic_set_irq1(&s->pics[irq>>   3], irq&   7, level);
>>           pic_update_irq(s);
>>           trace_kvm_pic_set_irq(irq>>   3, irq&   7, s->pics[irq>>   3].elcr,
>>
>>
>>
>> While it's still working I see this here with the levels changing 0-1-0.
>> Though then it stops and levels are only at '1'.
>>
>> [ 1773.833824] kvm_pic_set_irq
>> [ 1773.833827] pic_set_irq1 131: level=0, irr = 5b
>> [ 1773.834161] kvm_pic_set_irq
>> [ 1773.834163] pic_set_irq1 131: level=1, irr = 5b
>> [ 1773.834193] kvm_pic_set_irq
>> [ 1773.834195] pic_set_irq1 131: level=0, irr = 5b
>> [ 1773.835028] kvm_pic_set_irq
>> [ 1773.835031] pic_set_irq1 131: level=1, irr = 5b
>> [ 1773.835542] kvm_pic_set_irq
>> [ 1773.835545] pic_set_irq1 131: level=1, irr = 5b
>> [ 1773.889892] kvm_pic_set_irq
>> [ 1773.889894] pic_set_irq1 131: level=1, irr = 5b
>> [ 1791.258793] pic_set_irq1 119: level=1, irr = d9
>> [ 1791.258824] pic_set_irq1 119: level=0, irr = d1
>> [ 1791.402476] pic_set_irq1 119: level=1, irr = d9
>> [ 1791.402534] pic_set_irq1 119: level=0, irr = d1
>> [ 1791.402538] pic_set_irq1 119: level=1, irr = d9
>> [...]
>>
>>
>> I believe the last 5 shown calls can be ignored. After that the
>> interrupts don't go through anymore.
>>
>> In the device model I see interrupts being raised and cleared. After the
>> last one was cleared in 'my' device model, only interrupts are raised.
>> This looks like as if the interrupt handler in the guest Linux was never
>> run, thus the IRQ is never cleared and we're stuck.
>>
> User space is responsible for both setting and clearing that line. IRQ3
> means you are using some serial device model? Then you should check what
> its state is.
Good hint. I moved it now to IRQ11 and it works fine now (with kvm-git) 
from what I can see. There was no UART on IRQ3 before, though, but 
certainly it was the wrong IRQ for it.
> Moreover, a complete picture of the kernel/user space interaction should
> be obtainable by using fstrace for capturing kvm events.
>
Should it be working on IRQ3? If so, I'd look into it when I get a chance...
    Stefan