Re: [PATCH v5 5/5] hw/arm/virt: Allow virt extensions with KVM

[Eric Auger <eric.auger@redhat.com>]

Hi Alyssa,
On 6/17/25 4:17 PM, Alyssa Ross wrote:
> Eric Auger <eric.auger@redhat.com> writes:
>
>> From: Haibo Xu <haibo.xu@linaro.org>
>>
>> Up to now virt support on guest has been only supported with TCG.
>> Now it becomes feasible to use it with KVM acceleration.
>>
>> Also check only in-kernel GICv3 is used along with KVM EL2.
>>
>> Signed-off-by: Haibo Xu <haibo.xu@linaro.org>
>> Signed-off-by: Miguel Luis <miguel.luis@oracle.com>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Hi!  From what I can tell, this will produce an error on hosts that
> don't support nested virtualization when QEMU is invoked with -accel
> kvm:tcg -machine virtualization=on, but I don't think that's the ideal
Thanks for reporting this issue. This is not an expected behavior. I
will respin hopefully this week so I will have give it a try.

What kind of error msg do you get?

Thanks

Eric
> behaviour.  It would make more sense for it to fall back to the first
> permitted accel option that does support running the machine as
> configured, so if hardware nested virtualization is not supported, it
> should fall back to TCG.
>
> I maintain an OS development environment that includes scripts for
> running images in QEMU, where running KVM on those images is a
> requirement.  Currently, those scripts simply force TCG on aarch64.
> With this change, to take advantage of KVM NV support, I'd have to try
> to identify in the script whether NV would be supported.  QEMU would be
> in a much better position to determine this and fall back to TCG if it's
> unsupported, like how the -accel option with multiple values usually
> works.