linux-kernel - Re: [RFC PATCH 1/2] KVM: arm64: Add PSCI SYSTEM

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Date: Tue, 12 Mar 2024 08:47:16 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: David Woodhouse <dwmw2@...radead.org>
Cc: linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	Jonathan Corbet <corbet@....net>, Marc Zyngier <maz@...nel.org>,
	James Morse <james.morse@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Zenghui Yu <yuzenghui@...wei.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	David Woodhouse <dwmw@...zon.co.uk>,
	Mostafa Saleh <smostafa@...gle.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvmarm@...ts.linux.dev, linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] KVM: arm64: Add PSCI SYSTEM_OFF2 function for
 hibernation

Hi,

On Tue, Mar 12, 2024 at 01:51:28PM +0000, David Woodhouse wrote:
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> The PSCI v1.3 specification (alpha) adds support for a SYSTEM_OFF2 function
> which is analogous to ACPI S4 state. This will allow hosting environments
> to determine that a guest is hibernated rather than just powered off, and
> ensure that they preserve the virtual environment appropriately to allow
> the guest to resume safely (or bump the hardware_signature in the FACS to
> trigger a clean reboot instead).
> 
> The beta version will be changed to say that PSCI_FEATURES returns a bit
> mask of the supported hibernate types, which is implemented here.

Have you considered doing the PSCI implementation in userspace? The
SMCCC filter [*] was added for this exact purpose. There are other
features being done in userspace (e.g. vCPU hotplug) built on
intercepting hypercalls, this seems to be a reasonable candidate too.

[*] https://docs.kernel.org/virt/kvm/devices/vm.html#attribute-kvm-arm-vm-smccc-filter-w-o

-- 
Thanks,
Oliver