Hi All: We try pushing virtual iommu support for Xen guest and there are some features blocked by it.
Motivation: ----------------------- 1) Add SVM(Shared Virtual Memory) support for Xen guest To support iGFX pass-through for SVM enabled devices, it requires virtual iommu support to emulate related registers and intercept/handle guest SVM configure in the VMM. 2) Increase max vcpu support for one VM. So far, max vcpu for Xen hvm guest is 128. For HPC(High Performance Computing) cloud computing, it requires more vcpus support in a single VM. The usage model is to create just one VM on a machine with the same number vcpus as logical cpus on the host and pin vcpu on each logical cpu in order to get good compute performance. Intel Xeon phi KNL(Knights Landing) is dedicated to HPC market and supports 288 logical cpus. So we hope VM can support 288 vcpu to meet HPC requirement. Current Linux kernel requires IR(interrupt remapping) when MAX APIC ID is > 255 because interrupt only can be delivered among 0~255 cpus without IR. IR in VM relies on the virtual iommu support. KVM Virtual iommu support status ------------------------ Current, Qemu has a basic virtual iommu to do address translation for virtual device and it only works for the Q35 machine type. KVM reuses it and Redhat is adding IR to support more than 255 vcpus. How to add virtual iommu for Xen? ------------------------- First idea came to my mind is to reuse Qemu virtual iommu but Xen didn't support Q35 so far. Enabling Q35 for Xen seems not a short term task. Anthony did some related jobs before. I'd like to see your comments about how to implement virtual iommu for Xen. 1) Reuse Qemu virtual iommu or write a separate one for Xen? 2) Enable Q35 for Xen to reuse Qemu virtual iommu? Your comments are very appreciated. Thanks a lot. -- Best regards Tianyu Lan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel