On 05/05/19 04:06, Peter Xu wrote: >> I wonder if it's possible to untangle this and make the irqchip >> option stop affecting guest ABI on 4.1+ machine-types? This way >> QEMU could choose smarter defaults in the future without the >> compatibility code hassle. > Hi, Eduardo, > > Do you mean to enable IOMMU IR for kernel-irqchip=on? If so, I would > say it's not trivial... The major issue is that we probably need to > explicitly kick QEMU for every kernel IOAPIC setups since QEMU is the > only one who knows everything about interrupt remapping, while KVM > don't even have such a mechanism so far.
Right, it's not easy and it would be anyway possible only on kernels. There would have to be a mechanism to setup IOAPIC->MSI routes, similar to irqchip=split, and as Peter mentions an MMIO exit on writes to the routing table. Paolo
