Hi everyone. Will be grateful for some insight if I am on the right path :) On Mon, Nov 18, 2024 at 11:30 PM Ajay Garg <ajaygargnsit@xxxxxxxxx> wrote: > > Hi everyone. > > I understand in a para-virtualization environment, VMM maintains a > shadow-page-table (SPT) per process per guest, for GVA => HPA > translation. The hardware/MMU is passed a single pointer to this > shadow-page-table. The guest is aware that it is running in a > virtualization environment, and communicates with VMM to help maintain > the shadow-page-table. > > In full-virtualization/HVM virtualization, the guest is unaware that > it is running in a virtualized environment, and all GVA => GPA are > private. The VMM is obviously aware of all HVA => HPA mappings; plus > GPA => HVA is trivial as it's only an offset difference (Extended Page > Table, EPT). The hardware/MMU is passed three things : > > * Pointer to guest page-table, for GVA => GPA. > * Offset, for GPA => HVA. > * Pointer to host page-table, for HVA => HPA. > > In both the above cases, DMA is a challenge (without IOMMU), as > device-addresses would need to be physically-contiguous. This would in > turn mean that all of GPA needs to be physically-contiguous, which in > turn means that the host would need to spawn guest-process with all of > memory (HVA) which is physically-contiguous - very hard to meet > generally. > > *_Kindly correct me if I have made a mistake so far at conceptual level._* > > > Now, enters IOMMU, providing the ability to DMA with non-contiguous > device-addresses. > Now, my queries are simple : > > * > Is IOMMU DMA-Remapping mode (DMAR) analogous to a para-virtualization > environment (as per previous brief context)? > > * > Is IOMMU Pass-through (PT) mode analogous to a HVM environment (as per > previous brief context)? > > > Many thanks in advance for your time; hopefully I have not been a > complete idiot .. > > > Thanks and Regards, > Ajay
