linux-kernel - Re: [PATCH v4 1/6] firmware/psci: Add definitions for PSCI v1.3 specification

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Message-ID: <378d3797a94df5df655d47b3bd733da8853cc2e4.camel@infradead.org>
Date: Fri, 27 Sep 2024 15:24:45 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Miguel Luis <miguel.luis@...cle.com>
Cc: Souvik Chakravarty <Souvik.Chakravarty@....com>, 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>, 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>,  "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>
Subject: Re: [PATCH v4 1/6] firmware/psci: Add definitions for PSCI v1.3
 specification

On Fri, 2024-09-27 at 12:43 +0000, Miguel Luis wrote:
> 
> The common factor being the bit offset in the bitmap for SYSTEM_OFF2 discovery
> and argument to call SYSTEM_OFF2 as well. Would it be clearer something like:
> 
> #define  PSCI_1_3_HIBERNATE_TYPE_OFF BIT(0)

I've updated the tree at
https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/psci-hibernate
to do it that way.

As I did so, I realised that KVM *does* care about the argument to
SYSTEM_OFF2. This is a straight copy of the SYSTEM_RESET2 handling.
Although it doesn't pass the argument up to userspace (presumably
userspace is expected to look at the registers if it cares), it *does*
check it's within the range of permitted values and return
PSCI_RET_INVALID_PARAMS if not.

I've changed that check to:

		arg = smccc_get_arg1(vcpu);
		/*
		 * Permit zero to mean HIBERNATE_OFF as well as the bitmap
		 * form which was introduced in PSCI v1.3 beta.
		 */
		if (arg && arg != PSCI_1_3_HIBERNATE_TYPE_OFF) {
			val = PSCI_RET_INVALID_PARAMS;
			break;
		}
		kvm_psci_system_off2(vcpu);

On the guest side, I've changed the invocation to:

static int psci_sys_hibernate(struct sys_off_data *data)
{
	/*
	 * Zero is an acceptable alternative to PSCI_1_3_HIBERNATE_TYPE_OFF
	 * and is supported by hypervisors implementing an earlier version
	 * of the pSCI v1.3 spec.
	 */
	if (system_entering_hibernation())
		invoke_psci_fn(PSCI_FN_NATIVE(1_3, SYSTEM_OFF2),
			       0 /*PSCI_1_3_HIBERNATE_TYPE_OFF*/, 0, 0);
	return NOTIFY_DONE;
}

I'm going to do some careful interop testing with existing and new
hypervisors before reposting this version.

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