Re: [Xen-devel] Xen 4.5 random freeze question

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> Hi Stefano,
> 
> On Wed, Nov 19, 2014 at 7:07 PM, Stefano Stabellini
> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> > I think that's OK: it looks like that on your board for some reasons
> > when UIE is set you get irq 1023 (spurious interrupt) instead of your
> > normal maintenance interrupt.
> 
> OK, but I think this should be investigated too. What do you think ?

I think it is harmless: my guess is that if we clear UIE before reading
GICC_IAR, GICC_IAR returns spurious interrupt instead of maintenance
interrupt. But it doesn't really matter to us.

> >
> > But everything should work anyway without issues.
> >
> > This is the same patch as before but on top of the lastest xen-unstable
> > tree. Please confirm if it works.
> >
> > diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> > index 70d10d6..df140b9 100644
> > --- a/xen/arch/arm/gic.c
> > +++ b/xen/arch/arm/gic.c
> > @@ -403,6 +403,8 @@ void gic_clear_lrs(struct vcpu *v)
> >      if ( is_idle_vcpu(v) )
> >          return;
> >
> > +    gic_hw_ops->update_hcr_status(GICH_HCR_UIE, 0);
> > +
> >      spin_lock_irqsave(&v->arch.vgic.lock, flags);
> >
> >      while ((i = find_next_bit((const unsigned long *) &this_cpu(lr_mask),
> > @@ -527,8 +529,6 @@ void gic_inject(void)
> >
> >      if ( !list_empty(&current->arch.vgic.lr_pending) && lr_all_full() )
> >          gic_hw_ops->update_hcr_status(GICH_HCR_UIE, 1);
> > -    else
> > -        gic_hw_ops->update_hcr_status(GICH_HCR_UIE, 0);
> >  }
> >
> 
> I confirm - it works fine. Will this be a final fix ?

Yep :-)
Many thanks for your help on this!


> Regards,
> Andrii
> 
> >  static void do_sgi(struct cpu_user_regs *regs, enum gic_sgi sgi)
> >
> > On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> >> I got this strange log:
> >>
> >> (XEN) received maintenance interrupt irq=1023
> >>
> >> And platform does not hang due to this:
> >> +    hcr = GICH[GICH_HCR];
> >> +    if ( hcr & GICH_HCR_UIE )
> >> +    {
> >> +        GICH[GICH_HCR] &= ~GICH_HCR_UIE;
> >> +        uie_on = 1;
> >> +    }
> >>
> >> On Wed, Nov 19, 2014 at 6:50 PM, Stefano Stabellini
> >> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> > On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> >> >> On Wed, Nov 19, 2014 at 6:13 PM, Stefano Stabellini
> >> >> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> >> > On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> >> >> >> On Wed, Nov 19, 2014 at 6:01 PM, Andrii Tseglytskyi
> >> >> >> <andrii.tseglytskyi@xxxxxxxxxxxxxxx> wrote:
> >> >> >> > On Wed, Nov 19, 2014 at 5:41 PM, Stefano Stabellini
> >> >> >> > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> >> >> >> On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> >> >> >> >>> Hi Stefano,
> >> >> >> >>>
> >> >> >> >>> On Wed, Nov 19, 2014 at 4:52 PM, Stefano Stabellini
> >> >> >> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
> >> >> >> >>> > On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> >> >> >> >>> >> Hi Stefano,
> >> >> >> >>> >>
> >> >> >> >>> >> > >      if ( !list_empty(&current->arch.vgic.lr_pending) && 
> >> >> >> >>> >> > > lr_all_full() )
> >> >> >> >>> >> > > -        GICH[GICH_HCR] |= GICH_HCR_UIE;
> >> >> >> >>> >> > > +        GICH[GICH_HCR] |= GICH_HCR_NPIE;
> >> >> >> >>> >> > >      else
> >> >> >> >>> >> > > -        GICH[GICH_HCR] &= ~GICH_HCR_UIE;
> >> >> >> >>> >> > > +        GICH[GICH_HCR] &= ~GICH_HCR_NPIE;
> >> >> >> >>> >> > >
> >> >> >> >>> >> > >  }
> >> >> >> >>> >> >
> >> >> >> >>> >> > Yes, exactly
> >> >> >> >>> >>
> >> >> >> >>> >> I tried, hang still occurs with this change
> >> >> >> >>> >
> >> >> >> >>> > We need to figure out why during the hang you still have all 
> >> >> >> >>> > the LRs
> >> >> >> >>> > busy even if you are getting maintenance interrupts that 
> >> >> >> >>> > should cause
> >> >> >> >>> > them to be cleared.
> >> >> >> >>> >
> >> >> >> >>>
> >> >> >> >>> I see that I have free LRs during maintenance interrupt
> >> >> >> >>>
> >> >> >> >>> (XEN) gic.c:871:d0v0 maintenance interrupt
> >> >> >> >>> (XEN) GICH_LRs (vcpu 0) mask=0
> >> >> >> >>> (XEN)    HW_LR[0]=9a015856
> >> >> >> >>> (XEN)    HW_LR[1]=0
> >> >> >> >>> (XEN)    HW_LR[2]=0
> >> >> >> >>> (XEN)    HW_LR[3]=0
> >> >> >> >>> (XEN) Inflight irq=86 lr=0
> >> >> >> >>> (XEN) Inflight irq=2 lr=255
> >> >> >> >>> (XEN) Pending irq=2
> >> >> >> >>>
> >> >> >> >>> But I see that after I got hang - maintenance interrupts are 
> >> >> >> >>> generated
> >> >> >> >>> continuously. Platform continues printing the same log till 
> >> >> >> >>> reboot.
> >> >> >> >>
> >> >> >> >> Exactly the same log? As in the one above you just pasted?
> >> >> >> >> That is very very suspicious.
> >> >> >> >
> >> >> >> > Yes exactly the same log. And looks like it means that LRs are 
> >> >> >> > flushed
> >> >> >> > correctly.
> >> >> >> >
> >> >> >> >>
> >> >> >> >> I am thinking that we are not handling GICH_HCR_UIE correctly and
> >> >> >> >> something we do in Xen, maybe writing to an LR register, might 
> >> >> >> >> trigger a
> >> >> >> >> new maintenance interrupt immediately causing an infinite loop.
> >> >> >> >>
> >> >> >> >
> >> >> >> > Yes, this is what I'm thinking about. Taking in account all 
> >> >> >> > collected
> >> >> >> > debug info it looks like once LRs are overloaded with SGIs -
> >> >> >> > maintenance interrupt occurs.
> >> >> >> > And then it is not handled properly, and occurs again and again - 
> >> >> >> > so
> >> >> >> > platform hangs inside its handler.
> >> >> >> >
> >> >> >> >> Could you please try this patch? It disable GICH_HCR_UIE 
> >> >> >> >> immediately on
> >> >> >> >> hypervisor entry.
> >> >> >> >>
> >> >> >> >
> >> >> >> > Now trying.
> >> >> >> >
> >> >> >> >>
> >> >> >> >> diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> >> >> >> >> index 4d2a92d..6ae8dc4 100644
> >> >> >> >> --- a/xen/arch/arm/gic.c
> >> >> >> >> +++ b/xen/arch/arm/gic.c
> >> >> >> >> @@ -701,6 +701,8 @@ void gic_clear_lrs(struct vcpu *v)
> >> >> >> >>      if ( is_idle_vcpu(v) )
> >> >> >> >>          return;
> >> >> >> >>
> >> >> >> >> +    GICH[GICH_HCR] &= ~GICH_HCR_UIE;
> >> >> >> >> +
> >> >> >> >>      spin_lock_irqsave(&v->arch.vgic.lock, flags);
> >> >> >> >>
> >> >> >> >>      while ((i = find_next_bit((const unsigned long *) 
> >> >> >> >> &this_cpu(lr_mask),
> >> >> >> >> @@ -821,12 +823,8 @@ void gic_inject(void)
> >> >> >> >>
> >> >> >> >>      gic_restore_pending_irqs(current);
> >> >> >> >>
> >> >> >> >> -
> >> >> >> >>      if ( !list_empty(&current->arch.vgic.lr_pending) && 
> >> >> >> >> lr_all_full() )
> >> >> >> >>          GICH[GICH_HCR] |= GICH_HCR_UIE;
> >> >> >> >> -    else
> >> >> >> >> -        GICH[GICH_HCR] &= ~GICH_HCR_UIE;
> >> >> >> >> -
> >> >> >> >>  }
> >> >> >> >>
> >> >> >> >>  static void do_sgi(struct cpu_user_regs *regs, int othercpu, 
> >> >> >> >> enum gic_sgi sgi)
> >> >> >> >
> >> >> >>
> >> >> >> Heh - I don't see hangs with this patch :) But also I see that
> >> >> >> maintenance interrupt doesn't occur (and no hang as result)
> >> >> >> Stefano - is this expected?
> >> >> >
> >> >> > No maintenance interrupts at all? That's strange. You should be
> >> >> > receiving them when LRs are full and you still have interrupts pending
> >> >> > to be added to them.
> >> >> >
> >> >> > You could add another printk here to see if you should be receiving
> >> >> > them:
> >> >> >
> >> >> >      if ( !list_empty(&current->arch.vgic.lr_pending) && 
> >> >> > lr_all_full() )
> >> >> > +    {
> >> >> > +        gdprintk(XENLOG_DEBUG, "requesting maintenance interrupt\n");
> >> >> >          GICH[GICH_HCR] |= GICH_HCR_UIE;
> >> >> > -    else
> >> >> > -        GICH[GICH_HCR] &= ~GICH_HCR_UIE;
> >> >> > -
> >> >> > +    }
> >> >> >  }
> >> >> >
> >> >>
> >> >> Requested properly:
> >> >>
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >> (XEN) gic.c:756:d0v0 requesting maintenance interrupt
> >> >>
> >> >> But does not occur
> >> >
> >> > OK, let's see what's going on then by printing the irq number of the
> >> > maintenance interrupt:
> >> >
> >> > diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
> >> > index 4d2a92d..fed3167 100644
> >> > --- a/xen/arch/arm/gic.c
> >> > +++ b/xen/arch/arm/gic.c
> >> > @@ -55,6 +55,7 @@ static struct {
> >> >  static DEFINE_PER_CPU(uint64_t, lr_mask);
> >> >
> >> >  static uint8_t nr_lrs;
> >> > +static bool uie_on;
> >> >  #define lr_all_full() (this_cpu(lr_mask) == ((1 << nr_lrs) - 1))
> >> >
> >> >  /* The GIC mapping of CPU interfaces does not necessarily match the
> >> > @@ -694,6 +695,7 @@ void gic_clear_lrs(struct vcpu *v)
> >> >  {
> >> >      int i = 0;
> >> >      unsigned long flags;
> >> > +    unsigned long hcr;
> >> >
> >> >      /* The idle domain has no LRs to be cleared. Since gic_restore_state
> >> >       * doesn't write any LR registers for the idle domain they could be
> >> > @@ -701,6 +703,13 @@ void gic_clear_lrs(struct vcpu *v)
> >> >      if ( is_idle_vcpu(v) )
> >> >          return;
> >> >
> >> > +    hcr = GICH[GICH_HCR];
> >> > +    if ( hcr & GICH_HCR_UIE )
> >> > +    {
> >> > +        GICH[GICH_HCR] &= ~GICH_HCR_UIE;
> >> > +        uie_on = 1;
> >> > +    }
> >> > +
> >> >      spin_lock_irqsave(&v->arch.vgic.lock, flags);
> >> >
> >> >      while ((i = find_next_bit((const unsigned long *) 
> >> > &this_cpu(lr_mask),
> >> > @@ -865,6 +873,11 @@ void gic_interrupt(struct cpu_user_regs *regs, int 
> >> > is_fiq)
> >> >          intack = GICC[GICC_IAR];
> >> >          irq = intack & GICC_IA_IRQ;
> >> >
> >> > +        if ( uie_on )
> >> > +        {
> >> > +            uie_on = 0;
> >> > +            printk("received maintenance interrupt irq=%d\n", irq);
> >> > +        }
> >> >          if ( likely(irq >= 16 && irq < 1021) )
> >> >          {
> >> >              local_irq_enable();
> >>
> >>
> >>
> >> --
> >>
> >> Andrii Tseglytskyi | Embedded Dev
> >> GlobalLogic
> >> www.globallogic.com
> >>
> 
> 
> 
> -- 
> 
> Andrii Tseglytskyi | Embedded Dev
> GlobalLogic
> www.globallogic.com
> 

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