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

[Jan Kiszka <jan.kiszka@web.de>]

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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.

Moreover, a complete picture of the kernel/user space interaction should
be obtainable by using fstrace for capturing kvm events.

Jan


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