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Part 1: Reworking the ARM GIC Emulation
The ARM Generic Interrupt Controller (GIC) provides some level of virtualization support in hardware. This still requires emulation of the distributor part, which has to integrate with the virtualization feature. Doing this in a performing and readable way is not trivial, especially the locking strategy tends to be complicated.
While extending the existing virtual GIC support in Xen to cover support for MSIs, some issues have been discovered which ask for some significant changes in the existing code.
The presentation will briefly describe the existing VGIC design and the issues we faced when trying to extend it. Based on this the changes will be presented and how they improve and ideally simplify the code.
Part 2: Xen Challenges in the ARM ITS Emulation
For being able to use MSIs on ARM systems in Xen domains we need to emulate the ARM GICv3 ITS controller. Its design is centered around a command queue located in normal system memory.
Emulating this in the Xen hypervisor brings some interesting challenges, ranging from safely accessing the guest memory and dealing with possible propagation of commands, to possible DOS attacks by domains keeping the emulation code busy.
The presentation outlines the main problems and how we hit Xen limits in emulating this correctly and efficiently. Also it presents our temporary workarounds and their drawbacks.