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
