On Mon, 13 Mar 2023, Jan Beulich wrote: > On 12.03.2023 13:01, Huang Rui wrote: > > Xen PVH is the paravirtualized mode and takes advantage of hardware > > virtualization support when possible. It will using the hardware IOMMU > > support instead of xen-swiotlb, so disable swiotlb if current domain is > > Xen PVH. > > But the kernel has no way (yet) to drive the IOMMU, so how can it get > away without resorting to swiotlb in certain cases (like I/O to an > address-restricted device)? I think Ray meant that, thanks to the IOMMU setup by Xen, there is no need for swiotlb-xen in Dom0. Address translations are done by the IOMMU so we can use guest physical addresses instead of machine addresses for DMA. This is a similar case to Dom0 on ARM when the IOMMU is available (see include/xen/arm/swiotlb-xen.h:xen_swiotlb_detect, the corresponding case is XENFEAT_not_direct_mapped). Jurgen, what do you think? Would you rather make xen_swiotlb_detect common between ARM and x86?
