On Mon, 2021-03-22 at 10:07 +0000, Haibo Xu wrote: > This series add support for ARMv8.3/8.4 nested virtualization support > in KVM mode. It's based on Marc Zyngier's kernel KVM patches[1], and > has been tested on a FVP model to run a L2 guest with Qemu. Now the > feature can be enabled by "-M virt,accel=kvm,virtualization=on" when > starting a VM.
Why the need to enable this explicitly? AFAIK, that's not necessary for any other architecture: on x86, you just need to make sure you're using '-cpu host' and pass a parameter to the kernel module. Even assuming this can't be enabled transparently, wouldn't its availability it be controlled by a CPU feature flag, similar to what already happens for SVE and PMU, rather than a machine type option? That would also address the discoverability issue: unless I'm mistaken (which I very well might be :), with the current implementation there's no way to tell whether nested KVM will be usable short of trying and seeing whether QEMU errors out. -- Andrea Bolognani / Red Hat / Virtualization
