On 04.10.21 12:24, Marc Zyngier wrote:
Hi Lukas,
Hi Mark, Thanks for your quick reply.
On Mon, 04 Oct 2021 11:07:47 +0100, Lukas Jünger <lukas.juenger@xxxxxxxxxxxxxxxxxx> wrote:Hello, I am trying to run an emulator that uses KVM on arm64 to execute code. The emulator contains a userspace model of a GICv2 IRQ controller. The platform that I am running on (n1sdp) has aN1-SDP? My condolences...
Is there more to this?
I'm not using an in-kernel irq controller, at least I don't set one up. This is all custom, so no QEMU etc. The GICv2 is also a custom model that lives in user space. The guest gets a DT telling it that there is a GICv2 and it should access it via MMIO. This all used to work on Raspberry Pi 3 and Socionext Synquacer. The port to N1-SDP is giving me trouble. I understand why it is tainting the kernel, I was just wondering if I could somehow tell KVM to set this up correctly, e.g. by setting the ICC_SRE_ELx.GICv3. When I boot Linux in the emulator I run into gic_check_cpu_features() in drivers/irqchip/irq-gic.c, which taints the kernel as the host uses system registers to communicate with the host GICv3. I saw that ICC_SRE_ELx can be used to force MMIO, but setting this from inside the VM did not work and using KVM_SET_ONE_REG failed with error.N1-SDP doesn't implement the MMIO interface at all, and our GIC emulation doesn't either. Both are valid implementations.Is there a way to use a userspace GICv2 model with KVM on a GICv3 host without tainting?The tainting happens because you have created a VM with a GICv3 irqchip (at some point, your VMM calls into KVM to create a device with the KVM_DEV_TYPE_ARM_VGIC_V3 attribute). The guest then sees that GICv3 is enabled (ICC_SRE_ELx.SRE==1), and yet you somehow expose a GICv2 to the guest (either via DT or ACPI). That's illegal. If you want a userspace interrupt controller, you need prevent the creation of an in-kernel interrupt controller, which is a change in your VMM or maybe a configuration change.
M.
Best regards, Lukas
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