linux-kernel - Re: [PATCH v6 6/6] arm64: Use SYSTEM_OFF2 PSCI call to power off for hibernate

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Message-ID: <ZxprcWDe2AXuLhD_@linux.dev>
Date: Thu, 24 Oct 2024 08:44:49 -0700
From: Oliver Upton <oliver.upton@...ux.dev>
To: David Woodhouse <dwmw2@...radead.org>
Cc: Miguel Luis <miguel.luis@...cle.com>,
	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>,
	Pavel Machek <pavel@....cz>, Len Brown <len.brown@...el.com>,
	Shuah Khan <shuah@...nel.org>, David Woodhouse <dwmw@...zon.co.uk>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
	Francesco Lavra <francescolavra.fl@...il.com>
Subject: Re: [PATCH v6 6/6] arm64: Use SYSTEM_OFF2 PSCI call to power off for
 hibernate

Hi,

On Thu, Oct 24, 2024 at 03:48:26PM +0200, David Woodhouse wrote:
> On 24 October 2024 14:54:41 CEST, Miguel Luis <miguel.luis@...cle.com> wrote:
> >Perhaps spec. F.b. could be accommodated by first invoking SYSTEM_OFF2 with
> >PSCI_1_3_OFF_TYPE_HIBERNATE_OFF and checking its return value in case of a
> >fallback to an invocation with 0x0 ?

This already complies with F.b.

The PSCI implementation is required to accept either 0 or 1 for
HIBERNATE_OFF. Using 0 seems like a good choice for compatibility since ...

> I wasn't aware there was any point. Are there any hypervisors which actually implemented it that way? Amazon Linux and Ubuntu guests already just use zero.
> 
> We could add it later if such a hypervisor (now in violation of F.b) turns up, I suppose?

IIUC, you're really wanting to 0x0 because there are hypervisors out
there that violate the final spec and *only* accept this value.

That's perfectly fine, but it'd help avoid confusion if the supporting
comment was a bit more direct:

	/*
	 * If no hibernate type is specified SYSTEM_OFF2 defaults to
	 * selecting HIBERNATE_OFF.
	 *
	 * There are hypervisors in the wild that violate the spec and
	 * reject calls that explicitly provide a hibernate type. For
	 * compatibility with these nonstandard implementations, pass 0
	 * as the type.
	 */
	 if (system_entering_hibernation())
		invoke_psci_fn(PSCI_FN_NATIVE(1_3, SYSTEM_OFF2), 0 , 0, 0);

Thoughts?

-- 
Thanks,
Oliver