Re: [PATCH 2/2] hw/intc: Have ARM_GIC select ARM_GICV3 when KVM is not available

[Phil Dennis-Jordan <phil@philjordan.eu>]

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On Sat, 28 Dec 2024 at 11:48, Phil Dennis-Jordan <phil@philjordan.eu> wrote:

>
>
> On Fri, 27 Dec 2024 at 21:24, Philippe Mathieu-Daudé <philmd@linaro.org>
> wrote:
>
>> When the KVM accelerator is selected, the Kconfig ARM_GIC key
>> selects the KVM GIC implementation (ARM_GIC_KVM).
>> For other accelerators (TCG, HVF, ...), select the generic
>> implementation.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
>> ---
>>  hw/intc/Kconfig | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/hw/intc/Kconfig b/hw/intc/Kconfig
>> index 7547528f2c2..762139d8df3 100644
>> --- a/hw/intc/Kconfig
>> +++ b/hw/intc/Kconfig
>> @@ -23,7 +23,7 @@ config APIC
>>
>>  config ARM_GIC
>>      bool
>> -    select ARM_GICV3 if TCG
>> +    select ARM_GICV3 if !KVM
>>
>
> Wouldn't this disable the ARM_GICV3 by default when building with
> --enable-tcg --enable-kvm? And then there would be no GIC available when
> running the built QEMU in TCG mode. (Bear with me, I'm a relative Meson
> newbie.)
>
>


OK, I've managed to answer my own question now by setting up a RPi5 with
aarch64 RPOS and building QEMU on that with --enable-kvm --enable-tcg. With
patch 1/2 applied on current upstream master, I get:

$ build/qemu-system-aarch64 -accel tcg -M virt,gic-version=3 -smp 4 -m 4G
*[runs successfully]*

with 2/2 applied as well:

$ build/qemu-system-aarch64 -accel tcg -M virt,gic-version=3 -smp 4 -m 4G
qemu-system-aarch64: tcg does not support GICv3 emulation
$

In other words, with the proposed change, ARM_GICV3 is indeed deselected if
KVM is selected even if TCG is also selected.


Possibly very basic question: is there any support for kernel-irqchip=off
on aarch64/KVM?
If yes, don't we need ARM_GICV3 in that case anyway, so we should drop any
accel dependency on it in the first place?


If we definitely don't need the software GIC in KVM-only builds, I guess
we're down to listing each accel that needs it individually. Is that:

select ARM_GICV3 if TCG || HVF || NVMM || WHPX || XEN_EMU || XEN

or can we drop any of those? Have I missed anything? What about QTest?

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