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

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Message-ID: <23C91005-7304-4312-A5E0-F5E6C05B3209@oracle.com>
Date: Thu, 24 Oct 2024 12:54:41 +0000
From: Miguel Luis <miguel.luis@...cle.com>
To: David Woodhouse <dwmw2@...radead.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>,
        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 David,

> On 19 Oct 2024, at 17:15, David Woodhouse <dwmw2@...radead.org> wrote:
> 
> From: David Woodhouse <dwmw@...zon.co.uk>
> 
> The PSCI v1.3 specification 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 handle that state appropriately on subsequent launches.
> 
> Since commit 60c0d45a7f7a ("efi/arm64: use UEFI for system reset and
> poweroff") the EFI shutdown method is deliberately preferred over PSCI
> or other methods. So register a SYS_OFF_MODE_POWER_OFF handler which
> *only* handles the hibernation, leaving the original PSCI SYSTEM_OFF as
> a last resort via the legacy pm_power_off function pointer.
> 
> The hibernation code already exports a system_entering_hibernation()
> function which is be used by the higher-priority handler to check for
> hibernation. That existing function just returns the value of a static
> boolean variable from hibernate.c, which was previously only set in the
> hibernation_platform_enter() code path. Set the same flag in the simpler
> code path around the call to kernel_power_off() too.
> 
> An alternative way to hook SYSTEM_OFF2 into the hibernation code would
> be to register a platform_hibernation_ops structure with an ->enter()
> method which makes the new SYSTEM_OFF2 call. But that would have the
> unwanted side-effect of making hibernation take a completely different
> code path in hibernation_platform_enter(), invoking a lot of special dpm
> callbacks.
> 
> Another option might be to add a new SYS_OFF_MODE_HIBERNATE mode, with
> fallback to SYS_OFF_MODE_POWER_OFF. Or to use the sys_off_data to
> indicate whether the power off is for hibernation.
> 
> But this version works and is relatively simple.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>
> Acked-by: Rafael J. Wysocki <rafael@...nel.org>
> ---
> drivers/firmware/psci/psci.c | 42 ++++++++++++++++++++++++++++++++++++
> kernel/power/hibernate.c     |  5 ++++-
> 2 files changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> index 2328ca58bba6..8809455a61a6 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -78,6 +78,7 @@ struct psci_0_1_function_ids get_psci_0_1_function_ids(void)
> 
> static u32 psci_cpu_suspend_feature;
> static bool psci_system_reset2_supported;
> +static bool psci_system_off2_hibernate_supported;
> 
> static inline bool psci_has_ext_power_state(void)
> {
> @@ -333,6 +334,33 @@ static void psci_sys_poweroff(void)
> invoke_psci_fn(PSCI_0_2_FN_SYSTEM_OFF, 0, 0, 0);
> }
> 
> +#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.

s/pSCI/PSCI

> + */
> + if (system_entering_hibernation())
> + invoke_psci_fn(PSCI_FN_NATIVE(1_3, SYSTEM_OFF2),
> +       0 /*PSCI_1_3_OFF_TYPE_HIBERNATE_OFF*/, 0, 0);

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 ?

Thanks.
Miguel

> + return NOTIFY_DONE;
> +}
> +
> +static int __init psci_hibernate_init(void)
> +{
> + if (psci_system_off2_hibernate_supported) {
> + /* Higher priority than EFI shutdown, but only for hibernate */
> + register_sys_off_handler(SYS_OFF_MODE_POWER_OFF,
> + SYS_OFF_PRIO_FIRMWARE + 2,
> + psci_sys_hibernate, NULL);
> + }
> + return 0;
> +}
> +subsys_initcall(psci_hibernate_init);
> +#endif
> +
> static int psci_features(u32 psci_func_id)
> {
> return invoke_psci_fn(PSCI_1_0_FN_PSCI_FEATURES,
> @@ -364,6 +392,7 @@ static const struct {
> PSCI_ID_NATIVE(1_1, SYSTEM_RESET2),
> PSCI_ID(1_1, MEM_PROTECT),
> PSCI_ID_NATIVE(1_1, MEM_PROTECT_CHECK_RANGE),
> + PSCI_ID_NATIVE(1_3, SYSTEM_OFF2),
> };
> 
> static int psci_debugfs_read(struct seq_file *s, void *data)
> @@ -525,6 +554,18 @@ static void __init psci_init_system_reset2(void)
> psci_system_reset2_supported = true;
> }
> 
> +static void __init psci_init_system_off2(void)
> +{
> + int ret;
> +
> + ret = psci_features(PSCI_FN_NATIVE(1_3, SYSTEM_OFF2));
> + if (ret < 0)
> + return;
> +
> + if (ret & PSCI_1_3_OFF_TYPE_HIBERNATE_OFF)
> + psci_system_off2_hibernate_supported = true;
> +}
> +
> static void __init psci_init_system_suspend(void)
> {
> int ret;
> @@ -655,6 +696,7 @@ static int __init psci_probe(void)
> psci_init_cpu_suspend();
> psci_init_system_suspend();
> psci_init_system_reset2();
> + psci_init_system_off2();
> kvm_init_hyp_services();
> }
> 
> diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
> index e35829d36039..1f87aa01ba44 100644
> --- a/kernel/power/hibernate.c
> +++ b/kernel/power/hibernate.c
> @@ -685,8 +685,11 @@ static void power_down(void)
> }
> fallthrough;
> case HIBERNATION_SHUTDOWN:
> - if (kernel_can_power_off())
> + if (kernel_can_power_off()) {
> + entering_platform_hibernation = true;
> kernel_power_off();
> + entering_platform_hibernation = false;
> + }
> break;
> }
> kernel_halt();
> -- 
> 2.44.0
>