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

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Message-ID: <ZyUUh6KawapLkj0z@lpieralisi>
Date: Fri, 1 Nov 2024 18:48:55 +0100
From: Lorenzo Pieralisi <lpieralisi@...nel.org>
To: David Woodhouse <dwmw2@...radead.org>, sami.mujawar@....com,
	ardb@...nel.org
Cc: Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>,
	Marc Zyngier <maz@...nel.org>,
	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>,
	"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, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	kvmarm@...ts.linux.dev, linux-pm@...r.kernel.org,
	linux-kselftest@...r.kernel.org,
	Francesco Lavra <francescolavra.fl@...il.com>,
	Miguel Luis <miguel.luis@...cle.com>
Subject: Re: [PATCH v6 6/6] arm64: Use SYSTEM_OFF2 PSCI call to power off for
 hibernate

[+Ard, Sami, for EFI]

On Thu, Oct 31, 2024 at 06:55:43PM +0100, Lorenzo Pieralisi wrote:
> On Sat, Oct 19, 2024 at 06:15:47PM +0100, David Woodhouse wrote:
> 
> [...]
> 
> > +#ifdef CONFIG_HIBERNATION
> > +static int psci_sys_hibernate(struct sys_off_data *data)
> > +{
> > +	/*
> > +	 * Zero is an acceptable alternative to PSCI_1_3_OFF_TYPE_HIBERNATE_OFF
> > +	 * and is supported by hypervisors implementing an earlier version
> > +	 * of the pSCI v1.3 spec.
> > +	 */
> 
> It is obvious but with this patch applied a host kernel would start executing
> SYSTEM_OFF2 too if supported in firmware to hibernate, it is not a hypervisor
> only code path.
> 
> Related to that: is it now always safe to override
> 
> commit 60c0d45a7f7a ("efi/arm64: use UEFI for system reset and poweroff")
> 
> for hibernation ? It is not very clear to me why overriding PSCI for
> poweroff was the right thing to do - tried to follow that patch history but
> the question remains (it is related to UpdateCapsule() but I don't know
> how that applies to the hibernation use case).

RFC: It is unclear to me what happens in current mainline if we try to
hibernate with EFI runtime services enabled and a capsule update pending (we
issue EFI ResetSystem(EFI_RESET_SHUTDOWN,..) which might not be compatible
with the reset required by the pending capsule update request) what happens
in this case I don't know but at least the choice is all contained in
EFI firmware.

Then if in the same scenario now we are switching to PSCI SYSTEM_OFF2 for the
hibernate reset I suspect that what happens to the in-flight capsule
update requests strictly depends on what "reset" PSCI SYSTEM_OFF2 will
end up doing ?

I think this is just a corner case and it is unlikely it has been ever
tested (is it even possible ? Looking at EFI folks) - it would be good
to clarify it at least to make sure we understand this code path.

Thanks,
Lorenzo