Re: [PATCH v2] domctl: fix IRQ permission granting/revocation

[Ian Campbell <Ian.Campbell@eu.citrix.com>]

On Fri, 2014-12-12 at 11:03 +0000, Jan Beulich wrote:
> >>> On 12.12.14 at 11:49, <andrew.cooper3@citrix.com> wrote:
> > On 12/12/14 10:24, Jan Beulich wrote:
> >> Commit 545607eb3c ("x86: fix various issues with handling guest IRQs")
> >> wasn't really consistent in one respect: The granting of access to an
> >> IRQ shouldn't assume the pIRQ->IRQ translation to be the same in both
> >> domains. In fact it is wrong to assume that a translation is already/
> >> still in place at the time access is being granted/revoked.
> >>
> >> What is wanted is to translate the incoming pIRQ to an IRQ for
> >> the invoking domain (as the pIRQ is the only notion the invoking
> >> domain has of the IRQ), and grant the subject domain access to
> >> the resulting IRQ.
> >>
> >> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> > 
> > Should domain_pirq_to_irq() be using 0 as its default invalid value,
> > rather than -1?  irq 0 is a real irq and could plausibly be wanted to be
> > passed through to a guest.
> 
> Not on x86. If another architecture would ever need this, I think
> we'd need to audit all current users of domain_pirq_to_irq() before
> doing such a change.

FWIW on ARM (at least the versions we support, i.e. with the generic IRQ
controller) IRQ0 is an SGI (what x86 would call an IPI). It seems
unlikely we'd want to pass one of those through...

Ian.