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Re: [PATCH RESEND v2 0/6] target/arm: Add nested virtualization support

From: Andrew Jones
Subject: Re: [PATCH RESEND v2 0/6] target/arm: Add nested virtualization support
Date: Tue, 27 Apr 2021 11:54:58 +0200

On Tue, Apr 27, 2021 at 10:42:18AM +0100, Peter Maydell wrote:
> On Thu, 1 Apr 2021 at 13:55, Haibo Xu <haibo.xu@linaro.org> 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 -cpu host,el2=on" when
> > starting a VM.
> Why are we making the UI for "enable EL2 guest with KVM" different
> from that for "enable EL2 guest with TCG" ? Currently an EL2
> TCG guest is set up with "-M virt,virtualization=on", which then
> does everything it needs to enable virtualization on all the
> components on the board including the CPU.
> Unless there's a strong technical reason why KVM EL2 has to
> be different, I think we should use the same switch.

I agree we should use the same switch, but I think I'd prefer it be the
CPU switch instead of the machine switch, as it's a CPU feature. There are
some board properties too, like the maintenance interrupt, but we tend to
call a feature a CPU feature when it shows up in the CPU manual, e.g. the
PMU is also a CPU feature, even though it has a PPI.


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