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[question] hw/arm/virt: about the default gic-version in accelerated mod

From: Auger Eric
Subject: [question] hw/arm/virt: about the default gic-version in accelerated mode
Date: Tue, 28 Jan 2020 11:47:09 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0

Hi Peter,

When arm virt machine is run in accelerated mode with "-cpu host
-machine virt", the default gic version is 2.

I understand the rationale with TCG where we don't have MSI ITS
emulation along with GICv3 so we need to choose GICv2 to get GICv2M

However in KVM mode, I would have expected to see the host GIC probed to
set the same version on guest. Indeed most of our HW now have GICv3
without GICv2 compat mode so our default values lead to weird traces:

qemu-system-aarch64: PMU: KVM_SET_DEVICE_ATTR: Invalid argument
qemu-system-aarch64: failed to set irq for PMU

I would like to propose a patch to improve those errors and also suggest
a hint. But I also wanted to know whether you would accept to change the
default value with KVM and choose the host version instead of 2. For TCG
we would keep v2.



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