Re: Plan for /dev/ioasid RFC v2

[Jason Gunthorpe]

On Fri, Jun 18, 2021 at 03:47:51PM +0200, Joerg Roedel wrote:
> Hi Kevin,
> 
> On Thu, Jun 17, 2021 at 07:31:03AM +0000, Tian, Kevin wrote:
> > Now let's talk about the new IOMMU behavior:
> > 
> > -   A device is blocked from doing DMA to any resource outside of
> >     its group when it's probed by the IOMMU driver. This could be a
> >     special state w/o attaching to any domain, or a new special domain
> >     type which differentiates it from existing domain types (identity, 
> >     dma, or unmanged). Actually existing code already includes a
> >     IOMMU_DOMAIN_BLOCKED type but nobody uses it.
> 
> There is a reason for the default domain to exist: Devices which require
> RMRR mappings to be present. You can't just block all DMA from devices
> until a driver takes over, we put much effort into making sure there is
> not even a small window in time where RMRR regions (unity mapped regions
> on AMD) are not mapped.

Yes, I think the DMA blocking can only start around/after a VFIO type
driver has probed() and bound to a device in the group, not much
different from today.

Jason