linux-kernel - Re: [RFC PATCH 0/2] Add PSCI v1.3 SYSTEM

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Message-ID: <87wmq7pj6g.wl-maz@kernel.org>
Date: Tue, 12 Mar 2024 15:24:23 +0000
From: Marc Zyngier <maz@...nel.org>
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>,
	Oliver Upton <oliver.upton@...ux.dev>,
	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 0/2] Add PSCI v1.3 SYSTEM_OFF2 support for hibernation

On Tue, 12 Mar 2024 13:51:27 +0000,
David Woodhouse <dwmw2@...radead.org> wrote:
> 
> The upcoming PSCI v1.3 specification adds support for a SYSTEM_OFF2

Pointer to the spec? Crucially, this is in the Alpha state, meaning
that it is still subject to change [1].

> 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).
> 
> This adds support for it to KVM, and to the guest hibernate code.
> 
> Strictly, we should perhaps also allow the guest to detect PSCI v1.3, 
> but when v1.1 was added in commit 512865d83fd9 it was done 
> unconditionally, which seems wrong. Shouldn't we have a way for 
> userspace to control what gets exposed, rather than silently changing 
> the guest behaviour with newer host kernels? Should I add a 
> KVM_CAP_ARM_PSCI_VERSION?

Do you mean something like 85bd0ba1ff98?

	M.

[1] https://documentation-service.arm.com/static/65e59325837c4d065f6556a6

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