Re: [RFC PATCH 00/34] Running Qualcomm's Gunyah Guests via KVM in EL1

[Marc Zyngier <maz@kernel.org>]

On Thu, 24 Apr 2025 16:34:50 +0100,
Oliver Upton <oliver.upton@linux.dev> wrote:
> 
> On Thu, Apr 24, 2025 at 03:13:07PM +0100, Karim Manaouil wrote:
> > This series introduces the capability of running Gunyah guests via KVM on
> > Qualcomm SoCs shipped with Gunyah hypervisor [1] (e.g. RB3 Gen2).
> > 
> > The goal of this work is to port the existing Gunyah hypervisor support from a
> > standalone driver interface [2] to KVM, with the aim of leveraging as much of the
> > existing KVM infrastructure as possible to reduce duplication of effort around
> > memory management (e.g. guest_memfd), irqfd, and other core components.
> > 
> > In short, Gunyah is a Type-1 hypervisor, meaning that it runs independently of any
> > high-level OS kernel such as Linux and runs in a higher CPU privilege level than VMs.
> > Gunyah is shipped as firmware and guests typically talk with Gunyah via hypercalls.
> > KVM is designed to run as Type-2 hypervisor. This port allows KVM to run in EL1 and
> > serve as the interface for VM lifecycle management,while offloading virtualization
> > to Gunyah.
> 
> If you're keen on running your own hypervisor then I'm sorry, you get to
> deal with it soup to nuts. Other hypervisors (e.g. mshv) have their own
> kernel drivers for managing the host / UAPI parts of driving VMs.
> 
> The KVM arch interface is *internal* to KVM, not something to be
> (ab)used for cramming in a non-KVM hypervisor. KVM and other hypervisors
> can still share other bits of truly common infrastructure, like
> guest_memfd.
> 
> I understand the value in what you're trying to do, but if you want it
> to smell like KVM you may as well just let the user run it at EL2.

+1. KVM is not a generic interface for random third party hypervisors.

If you want to run KVM on your Qualcomm HW, boot at EL2, and enjoy the
real thing -- it is worth it. If Gunyah is what you want, then there
is enough code out there to use it with crosvm.

But mixing the two is not happening, sorry.

	M.

-- 
Without deviation from the norm, progress is not possible.