On Thu, Feb 25, 2021 at 12:54:57PM -0500, Peter Xu wrote: > I can't say I fully understand the whole rational behind 5cbf3264bc71, but that > commit still sounds reasonable to me, since I don't see why VFIO cannot do > VFIO_IOMMU_MAP_DMA upon another memory range that's neither anonymous memory > nor vfio mapped MMIO range. It is not so much it can't, more that it doesn't and doesn't need to. > In those cases, vm_pgoff namespace defined by vfio may not be true > anymore, iiuc. Since this series is proposing linking the VMA to an address_space all the vm_pgoffs must be in the same namespace > Or does it mean that we don't want to allow VFIO dma to those unknown memory > backends, for some reason? Correct. VFIO can map into the IOMMU PFNs it can get a reference to. pin_user_pages() works for the majority, special VFIO VMAs cover the rest, and everthing else must be blocked for security. Jason
