Re: [Xen-devel] Bug report and patch about IRQ freezing after gic_restore_state

[유재용 <jaeyong.yoo@xxxxxxxxxxx>]

> > Signed-off-by: Jaeyong Yoo 
> > --- 
> >  xen/arch/arm/domain.c |    4 ++-- 
> >  xen/arch/arm/gic.c    |    4 ++-- 
> >  2 files changed, 4 insertions(+), 4 deletions(-) 
> > diff --git a/xen/arch/arm/domain.c b/xen/arch/arm/domain.c 
> > index f71b582..2c3b132 100644 
> > --- a/xen/arch/arm/domain.c 
> > +++ b/xen/arch/arm/domain.c 
> > @@ -141,6 +141,8 @@ static void ctxt_switch_to(struct vcpu *n) 
> >      /* VGIC */ 
> >      gic_restore_state(n); 
> > +    local_irq_enable(); 
> > +
> 
> Could you move the local_irq_enable right after ctxt_switch_to?

Of course.
Just one small concern:
Would it be more efficient (i.e., less scheduling latency) if we enable irq 
right after gic_restore state similar to lock-breaking effect?

> 
> >      /* XXX VFP */ 
> >      /* XXX MPU */ 
> > @@ -215,8 +217,6 @@ static void schedule_tail(struct vcpu *prev) 
> >  { 
> >      ctxt_switch_from(prev); 
> > -    local_irq_enable(); 
> > - 
> >      /* TODO 
> >         update_runstate_area(current); 
> >      */ 
> > diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c 
> > index d4f0a43..8186ad8 100644 
> > --- a/xen/arch/arm/gic.c 
> > +++ b/xen/arch/arm/gic.c 
> > @@ -81,11 +81,11 @@ void gic_restore_state(struct vcpu *v) 
> >      if ( is_idle_vcpu(v) ) 
> >          return; 
> > -    spin_lock_irq(&gic.lock); 
> > +    spin_lock(&gic.lock); 
> >      this_cpu(lr_mask) = v->arch.lr_mask; 
> >      for ( i=0; i>          GICH[GICH_LR + i] = v->arch.gic_lr[i]; 
> > -    spin_unlock_irq(&gic.lock); 
> > +    spin_unlock(&gic.lock); 
> 
> As the IRQ is disabled and the GICH registers can only be modified by
> the current physical CPU, I think you can remove the spin_{,un}lock and
> replace it by a dsb.

dsb sounds ok.

> 
> >      GICH[GICH_APR] = v->arch.gic_apr; 
> >      GICH[GICH_HCR] = GICH_HCR_EN; 
> >      isb(); 
> 

Best,
Jaeyong

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