Re: [PATCH v6 00/26] KVM: arm64: Introduce pKVM hyp VM and vCPU state at EL2

From: Oliver Upton <oliver.upton@linux.dev>
To: Marc Zyngier <maz@kernel.org>
Cc: "Will Deacon" <will@kernel.org>,
	kvmarm@lists.linux.dev, "Sean Christopherson" <seanjc@google.com>,
	"Vincent Donnefort" <vdonnefort@google.com>,
	"Alexandru Elisei" <alexandru.elisei@arm.com>,
	"Catalin Marinas" <catalin.marinas@arm.com>,
	"Philippe Mathieu-Daudé" <philmd@linaro.org>,
	"James Morse" <james.morse@arm.com>,
	"Chao Peng" <chao.p.peng@linux.intel.com>,
	"Quentin Perret" <qperret@google.com>,
	"Suzuki K Poulose" <suzuki.poulose@arm.com>,
	"Mark Rutland" <mark.rutland@arm.com>,
	"Fuad Tabba" <tabba@google.com>,
	kernel-team@android.com, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 00/26] KVM: arm64: Introduce pKVM hyp VM and vCPU state at EL2
Date: Fri, 11 Nov 2022 19:42:46 +0000	[thread overview]
Message-ID: <Y26ltgCIObKpRTWx@google.com> (raw)
In-Reply-To: <86edu9ph3d.wl-maz@kernel.org>

On Fri, Nov 11, 2022 at 04:54:14PM +0000, Marc Zyngier wrote:
> On Thu, 10 Nov 2022 19:02:33 +0000,
> Will Deacon <will@kernel.org> wrote:
> > 
> > Hi all,
> > 
> > This is version six of the pKVM EL2 state series, extending the pKVM
> > hypervisor code so that it can dynamically instantiate and manage VM
> > data structures without the host being able to access them directly.
> > These structures consist of a hyp VM, a set of hyp vCPUs and the stage-2
> > page-table for the MMU. The pages used to hold the hypervisor structures
> > are returned to the host when the VM is destroyed.
> > 
> > Previous versions are archived at:
> > 
> >   Mega-patch: https://lore.kernel.org/kvmarm/20220519134204.5379-1-will@kernel.org/
> >   v2: https://lore.kernel.org/all/20220630135747.26983-1-will@kernel.org/
> >   v3: https://lore.kernel.org/kvmarm/20220914083500.5118-1-will@kernel.org/
> >   v4: https://lore.kernel.org/kvm/20221017115209.2099-1-will@kernel.org/
> >   v5: https://lore.kernel.org/r/20221020133827.5541-1-will@kernel.org
> > 
> > The changes since v5 include:
> > 
> >   * Fix teardown ordering so that the host 'kvm' structure remains pins
> >     while the memcache is being filled.
> > 
> >   * Fixed a kerneldoc typo.
> > 
> >   * Included a patch from Oliver to rework the 'pkvm_mem_transition'
> >     structure and it's handling of the completer address.
> > 
> >   * Tweaked some commit messages and added new R-b tags.
> > 
> > As before, the final patch is RFC since it illustrates a very naive use
> > of the new hypervisor structures and subsequent changes will improve on
> > this once we have the guest private memory story sorted out.
> > 
> > Oliver: I'm pretty sure we're going to need to revert your completer
> > address cleanup as soon as we have guest-host sharing. We want to keep
> > the 'pkvm_mem_transition' structure 'const', but we will only know the
> > host address (PA) after walking the guest stage-2 and so we're going to
> > want to track that separately. Anyway, I've included it here at the end
> > so Marc can decide what he wants to do!
> 
> Thanks, I guess... :-/
> 
> If this patch is going to be reverted, I'd rather not take it (without
> guest/host sharing, we don't have much of a hypervisor).

+1, I'm more than happy being told my patch doesn't work :)

Having said that, if there are parts of the design that I've whined
about that are intentional then please educate me. Some things haven't
been quite as obvious, but I know you folks have been working on this
feature for a while.

I probably need to give the full patch-bomb another read to get all the
context too.

--
Thanks,
Oliver

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