Re: [Xen-devel] [PATCH v6 19/36] ARM: VGIC: add vcpu_id to struct pending_irq

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 7 Apr 2017, Julien Grall wrote:
> Hi Andre,
> 
> On 04/07/2017 06:32 PM, Andre Przywara wrote:
> > The target CPU for an LPI is encoded in the interrupt translation table
> > entry, so can't be easily derived from just an LPI number (short of
> > walking *all* tables and find the matching LPI).
> > To avoid this in case we need to know the VCPU (for the INVALL command,
> > for instance), put the VCPU ID in the struct pending_irq, so that it is
> > easily accessible.
> > 
> > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> > ---
> >  xen/include/asm-arm/vgic.h | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/xen/include/asm-arm/vgic.h b/xen/include/asm-arm/vgic.h
> > index 86a1a89..9145b42 100644
> > --- a/xen/include/asm-arm/vgic.h
> > +++ b/xen/include/asm-arm/vgic.h
> > @@ -88,6 +88,9 @@ struct pending_irq
> >       * TODO: when implementing irq migration, taking only the current
> >       * vgic lock is not going to be enough. */
> >      struct list_head lr_queue;
> > +#ifdef CONFIG_HAS_ITS
> > +    uint16_t lpi_vcpu_id;          /* The VCPU for an LPI. */
> > +#endif
> 
> I am sorry, but in the current state this is a nack from me side. The
> pending_irq structure will increase by 8 bytes because of the alignment.
> 
> This will affect all the irq_pending as soon as CONFIG_HAS_ITS is enabled even
> if the platform is not using ITS.
> 
> Looking at the current usage it is only used by INVALL, which lead to confirm
> my first nack.
> 
> Please either find a hole in pending_irq or find an alternative solution.

Yeah, I was thinking the same thing. That is why I suggested the #ifdef
CONFIG_HAS_ITS. At least the problem would remain confined to ITS.

I recognize that we need a better solution, but I would be willing to
take this as-is with the ifdef for 4.9, assuming that everything else is
in order.

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