Re: [Qemu-ppc] [RFC PATCH 09/17] KVM: PPC64: booke: Hard disable interrupts when entering guest

[Caraman Mihai Claudiu-B02008]

> -----Original Message-----
> From: Linuxppc-dev [mailto:linuxppc-dev-
> address@hidden On Behalf Of
> Benjamin Herrenschmidt
> Sent: Thursday, July 05, 2012 1:21 AM
> To: Alexander Graf
> Cc: address@hidden List; Caraman Mihai Claudiu-B02008; linuxppc-dev;
> KVM list; <address@hidden>
> Subject: Re: [Qemu-ppc] [RFC PATCH 09/17] KVM: PPC64: booke: Hard disable
> interrupts when entering guest
> 
> On Wed, 2012-07-04 at 16:14 +0200, Alexander Graf wrote:
> > > +#ifdef CONFIG_64BIT
> > > +#define _hard_irq_disable() hard_irq_disable()
> > > +#else
> > > +#define _hard_irq_disable() local_irq_disable()
> > > +#endif
> >
> > So you only swap out the disable bit, but not the enable one? Ben,
> > would this work out?
> 
> hard_irq_disable() both soft and hard disable. local_irq_enable() will
> see that irqs are hard disabled and will hard enable.
> 
> However, there's a nastier discrepancy above: local_irq_disable will
> properly inform lockdep that we are disabling, while hard_irq_disable
> won't.
> 
> Arguably we might want to fix that inside hard_irq_disable() itself...
> 
> Also you need to be careful. If you are coming with interrupts already
> enabled, it's fine, but if you have interrupts soft disabled, then
> you hard disable, before you enter the guest you probably want to
> check if anything was left "pending" and cancel the entering of the
> guest if that is the case.

On which cases I can find interrupts soft disabled if I call local_irq_enable()
ahead? Can this happen when my kernel task is scheduled? 

I presume that if I call hard_irq_disable() before entering the guest, a guest 
exit
will find interrupts soft disabled.

-Mike