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

[Stefano Stabellini]

On Wed, 19 Nov 2014, Andrii Tseglytskyi wrote:
> Hi Stefano,
> 
> On Wed, Nov 19, 2014 at 4:52 PM, Stefano Stabellini
> <stefano.stabell...@eu.citrix.com> 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.

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.

Could you please try this patch? It disable GICH_HCR_UIE immediately on
hypervisor entry.


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)

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