From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5E57C11712; Thu, 19 Jun 2025 15:50:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750348238; cv=none; b=iWZtD/OdWeumqlWR0mft6fF6IdHutxaap7ZrIjUZlXzXfJ+9tmNDkMPakXo7C4CMCkEtsC8Hp+J/UNKKtUvJZKI9KHK4IokmMFtoIJ26QvyG26O3cxeonsZNVGCrct69jr2JhsePnaskP8d44Q3ljjTq2zIYGq4dzGVvmRtSkoQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750348238; c=relaxed/simple; bh=OKsVibEkSv+hfR4J2CvdJJEcDJm0d1G4pRgyEnSM5co=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=jl7Lg0aSc3Hn76/ad1gysn6TqUz78OB+LvHeJRH2jdv4ZaIBPt4e7FC99MT+CKHF0IZtvdxiAOE9lf2sCfDURdByTBAnPkss0cYRkqSKAcT7qJcrJe+jAt+kOJ/P9FtZpUvWBR2aWQCzLiUosRs93rirtEsln/qw7UDxHlHZZi0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=casper.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Bw9meWho; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=casper.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Bw9meWho" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=OKsVibEkSv+hfR4J2CvdJJEcDJm0d1G4pRgyEnSM5co=; b=Bw9meWhos1tgAIc+K/544bWYY7 TSrs4qSCCLwK/G59yXQbgmv2lmkCuMkvZxk0hrTtkOpznc9r9pAlYHynY14uNOPuXmJB9OwLNvUcI elmJR9YNWGf2mKdlNASMm/a1xOeU4qwTD53xc4HCErLoupHHCLNV6sLfS/JKHukPTXn8u0Ne2c922 zlvIs92esqPKGhjpXeteV0mf8YVWXMzWxaR7TBu4Qc6iFEwFrNIuSf9SW1Pvh6LVrFCB9HWPqvWkI NBuMIBtV0y3/yxRkY0iNJMEu8uJCBtlNxR6m78RVbQ/tXU7Yly1mqDneI+6opUUl0VPDw/pix9OXz zQZno7uA==; Received: from [2001:8b0:10b:5:748f:d833:d81c:4c8f] (helo=u09cd745991455d.ant.amazon.com) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uSHX4-00000009LhR-2ep8; Thu, 19 Jun 2025 15:50:30 +0000 Message-ID: Subject: Re: [RFC PATCH 00/34] Running Qualcomm's Gunyah Guests via KVM in EL1 From: David Woodhouse To: Marc Zyngier , Karim Manaouil , Oliver Upton Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, Alexander Graf , Alex Elder , Catalin Marinas , Fuad Tabba , Joey Gouly , Jonathan Corbet , Mark Brown , Mark Rutland , Paolo Bonzini , Prakruthi Deepak Heragu , Quentin Perret , Rob Herring , Srinivas Kandagatla , Srivatsa Vaddagiri , Will Deacon , Haripranesh S , Carl van Schaik , Murali Nalajala , Sreenivasulu Chalamcharla , Trilok Soni , Stefan Schmidt Date: Thu, 19 Jun 2025 16:50:29 +0100 In-Reply-To: <86ikmtjy51.wl-maz@kernel.org> References: <20250424141341.841734-1-karim.manaouil@linaro.org> <86ikmtjy51.wl-maz@kernel.org> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-8oYh6WC82njjqP/La6PW" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by casper.infradead.org. See http://www.infradead.org/rpr.html --=-8oYh6WC82njjqP/La6PW Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2025-04-24 at 17:57 +0100, Marc Zyngier wrote: > On Thu, 24 Apr 2025 16:34:50 +0100, > Oliver Upton wrote: > >=20 > > On Thu, Apr 24, 2025 at 03:13:07PM +0100, Karim Manaouil wrote: > > > This series introduces the capability of running Gunyah guests via KV= M on > > > Qualcomm SoCs shipped with Gunyah hypervisor [1] (e.g. RB3 Gen2). > > >=20 > > > The goal of this work is to port the existing Gunyah hypervisor suppo= rt 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 effo= rt around > > > memory management (e.g. guest_memfd), irqfd, and other core component= s. > > >=20 > > > In short, Gunyah is a Type-1 hypervisor, meaning that it runs indepen= dently 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 v= ia 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 v= irtualization > > > to Gunyah. > >=20 > > If you're keen on running your own hypervisor then I'm sorry, you get t= o > > 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. > >=20 > > The KVM arch interface is *internal* to KVM, not something to be > > (ab)used for cramming in a non-KVM hypervisor. KVM and other hypervisor= s > > can still share other bits of truly common infrastructure, like > > guest_memfd. > >=20 > > 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. >=20 > +1. KVM is not a generic interface for random third party hypervisors. I don't think that should be true in the general case. At least, it depends on whether you mean the literal implementation in arch/arm64/kvm/ vs. the userspace API and set of ioctls on /dev/kvm. The kernel exists to provide a coherent userspace API for all kinds of hardware. That's what it's *for*. It provides users with a consistent interface to all kinds of network cards, serial ports, etc. =E2=80=94 and t= hat includes firmware/platform features too.=20 There's no reason that shouldn't be the same for virtualisation. If the kernel cannot provide an API which supports *all* kinds of virtualization, then it seems like we've done something wrong. On x86 we have /dev/kvm backed by different vendor-specific support for Intel vs. AMD. And in recent years we've retrofitted confidential compute to it too, with SEV-SNP, TDX, etc. We haven't resorted to saying "no, sorry, KVM doesn't support that". 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