RE: [PATCH v2 0/4] Make the iommu driver no-snoop block feature consistent

Tian, Kevin
2022-04-12T02:49:22Z

> From: Robin Murphy <robin.murphy@arm.com>
> Sent: Friday, April 8, 2022 6:12 PM
>
> On 2022-04-08 10:08, Tian, Kevin wrote:
> >> From: Jason Gunthorpe <jgg@nvidia.com>
> >> Sent: Friday, April 8, 2022 3:08 AM
> >> On Thu, Apr 07, 2022 at 07:02:03PM +0100, Robin Murphy wrote:
> >>> On 2022-04-07 18:43, Jason Gunthorpe wrote:
> >>>> On Thu, Apr 07, 2022 at 06:03:37PM +0100, Robin Murphy wrote:
> >>>>> At a glance, this all looks about the right shape to me now, thanks!
> >>>>
> >>>> Thanks!
> >>>>
> >>>>> Ideally I'd hope patch #4 could go straight to device_iommu_capable()
> >> from
> >>>>> my Thunderbolt series, but we can figure that out in a couple of weeks
> >> once
> >>>>
> >>>> Yes, this does helps that because now the only iommu_capable call is
> >>>> in a context where a device is available :)
> >>>
> >>> Derp, of course I have *two* VFIO patches waiting, the other one
> touching
> >>> the iommu_capable() calls (there's still IOMMU_CAP_INTR_REMAP,
> which,
> >> much
> >>> as I hate it and would love to boot all that stuff over to
> >>> drivers/irqchip,
> >>
> >> Oh me too...
> >>
> >>> it's not in my way so I'm leaving it be for now). I'll have to rebase that
> >>> anyway, so merging this as-is is absolutely fine!
> >>
> >> This might help your effort - after this series and this below there
> >> are no 'bus' users of iommu_capable left at all.
> >>
> >
> > Out of curiosity, while iommu_capable is being moved to a per-device
> > interface what about irq_domain_check_msi_remap() below (which
> > is also a global check)?
>
> I suppose it could if anyone cared enough to make the effort - probably
> a case of resolving specific MSI domains for every device in the group,
> and potentially having to deal with hotplug later as well.
> Realistically, though, I wouldn't expect systems to have mixed
> capabilities in that regard (i.e. where the check would return false
> even though *some* domains support remapping), so there doesn't seem to
> be any pressing need to relax it.
>

Yes, that makes sense if no such example so far.