From: Marc Zyngier <maz@kernel.org>
To: "Lukas Jünger" <lukas.juenger@ice.rwth-aachen.de>
Cc: catalin.marinas@arm.com, will@kernel.org, kvmarm@lists.cs.columbia.edu
Subject: Re: KVM userspace GICv2 IRQ controller on platform with GICv3
Date: Mon, 04 Oct 2021 11:24:24 +0100 [thread overview]
Message-ID: <877detrstj.wl-maz@kernel.org> (raw)
In-Reply-To: <c3cff3de-61f6-0e19-6825-02c934dfbb76@ice.rwth-aachen.de>
Hi Lukas,
On Mon, 04 Oct 2021 11:07:47 +0100,
Lukas Jünger <lukas.juenger@ice.rwth-aachen.de> 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 a
N1-SDP? My condolences...
> 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.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-10-04 10:24 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-04 10:07 KVM userspace GICv2 IRQ controller on platform with GICv3 Lukas Jünger
2021-10-04 10:24 ` Marc Zyngier [this message]
2021-10-04 10:30 ` Lukas Jünger
2021-10-04 11:02 ` Marc Zyngier
2021-10-04 11:27 ` Lukas Jünger
2021-10-04 13:11 ` Marc Zyngier
2021-10-04 14:15 ` Lukas Jünger
2021-10-04 15:48 ` Marc Zyngier
2021-10-05 12:06 ` Lukas Jünger
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