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

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Message-ID: <86ikmtjy51.wl-maz@kernel.org>
Date: Thu, 24 Apr 2025 17:57:14 +0100
From: Marc Zyngier <maz@...nel.org>
To: Karim Manaouil <karim.manaouil@...aro.org>, Oliver Upton <oliver.upton@...ux.dev>
Cc: 	linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org,
	linux-arm-msm@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev,
	Alexander Graf <graf@...zon.com>,
	Alex Elder <elder@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Fuad Tabba <tabba@...gle.com>,
	Joey Gouly <joey.gouly@....com>,
	Jonathan Corbet <corbet@....net>,
	Mark Brown <broonie@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Prakruthi Deepak Heragu <quic_pheragu@...cinc.com>,
	Quentin Perret <qperret@...gle.com>,
	Rob Herring <robh@...nel.org>,
	Srinivas Kandagatla <srini@...nel.org>,
	Srivatsa Vaddagiri <quic_svaddagi@...cinc.com>,
	Will Deacon <will@...nel.org>,
	Haripranesh S <haripran@....qualcomm.com>,
	Carl van Schaik <cvanscha@....qualcomm.com>,
	Murali Nalajala <mnalajal@...cinc.com>,
	Sreenivasulu Chalamcharla <sreeniva@....qualcomm.com>,
	Trilok Soni <tsoni@...cinc.com>,
	Stefan Schmidt <stefan.schmidt@...aro.org>
Subject: Re: [RFC PATCH 00/34] Running Qualcomm's Gunyah Guests via KVM in EL1

On Thu, 24 Apr 2025 16:34:50 +0100,
Oliver Upton <oliver.upton@...ux.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.