Re: [PATCH 2/2] vfio: type1: conditionally check MSI remapping at irq domain level

[Mian Yousaf Kaukab]

On 03/02/2017 02:46 PM, Auger Eric wrote:
> Hi,
>
> On 02/03/2017 13:38, Mian Yousaf Kaukab wrote:
> > On 03/02/2017 11:24 AM, Auger Eric wrote:
> > > Hi,
> > >
> > > On 02/03/2017 11:01, Mian Yousaf Kaukab wrote:
> > > > Check only if irq domains are available.
> > > >
> > > > Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@xxxxxxxx>
> > > > ---
> > > >    drivers/vfio/vfio_iommu_type1.c | 5 +++--
> > > >    1 file changed, 3 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/drivers/vfio/vfio_iommu_type1.c
> > > > b/drivers/vfio/vfio_iommu_type1.c
> > > > index bd6f293c4ebd..e3ed50e40ead 100644
> > > > --- a/drivers/vfio/vfio_iommu_type1.c
> > > > +++ b/drivers/vfio/vfio_iommu_type1.c
> > > > @@ -1287,8 +1287,9 @@ static int vfio_iommu_type1_attach_group(void
> > > > *iommu_data,
> > > >        INIT_LIST_HEAD(&domain->group_list);
> > > >        list_add(&group->next, &domain->group_list);
> > > >    -    msi_remap = resv_msi ? irq_domain_check_msi_remap() :
> > > > -                iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
> > > > +    msi_remap = resv_msi && IS_ENABLED(CONFIG_IRQ_DOMAIN) ?
> > > > +            irq_domain_check_msi_remap() :
> > > > +            iommu_capable(bus, IOMMU_CAP_INTR_REMAP);
> > > Is that patch actually needed after [PATCH 1/2] irqdomain: add empty
> > > irq_domain_check_msi_remap. irq_domain_check_msi_remap() should be
> > > defined and if you follow my suggestion, would return false. Anyway in
> > > your case resv_msi should be false.
> > I agree its an overkill if resv_msi is guaranteed to be false. What I am
> > unsure about is that, if iommu have IOMMU_RESV_MSI regions that would
> > mean that irq domains are selected in the build. If this is not
> > guaranteed, then we need to add this check.
>
> Currently only ARM SMMUs advertise IOMMU_RESV_MSI regions. If attempting
> to do passthrough on an ARM platform not implementing IRQ_DOMAIN the
> unsafe IRQ assignment mode would need to be chosen (if
> irq_domain_check_msi_remap() returns false as discussed before). Anyway
> checking the  interrupt remapping capability on IOMMU side would report
> false as well since the capability is not exposed by ARM SMMU anymore.OK I will drop this patch. We get a warning anyway in case the 
capability is checked from the wrong place.

BR,
Yousaf