On Fri, Jun 18, 2021 at 12:15:06PM -0300, Jason Gunthorpe wrote: > 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. Does this mean when a device has a required "RMRR" that requires a unity mapping we block assigning those devices to guests? I remember we had some restriction but there was a need to go around it at some point in time. - Either we disallow assigning devices with RMRR - Break that unity map when the device is probed and after which any RMRR access from device will fault. Cheers, Ashok
