linux-kernel - [RFC PATCH 19/32] ACPI: Warn when the present bit changes but the feature is not enabled

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Date:   Fri,  3 Feb 2023 13:50:30 +0000
From:   James Morse <james.morse@....com>
To:     linux-pm@...r.kernel.org, loongarch@...ts.linux.dev,
        kvmarm@...ts.linux.dev, kvm@...r.kernel.org,
        linux-acpi@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, x86@...nel.org
Cc:     Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Huacai Chen <chenhuacai@...nel.org>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Len Brown <lenb@...nel.org>,
        Rafael Wysocki <rafael@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Salil Mehta <salil.mehta@...wei.com>,
        Russell King <linux@...linux.org.uk>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: [RFC PATCH 19/32] ACPI: Warn when the present bit changes but the feature is not enabled

ACPI firmware can trigger the events to add and remove CPUs, but the
OS may not support this.

Print a warning when this happens.

This gives early warning on arm64 systems that don't support
CONFIG_ACPI_HOTPLUG_PRESENT_CPU, as making CPUs not present has
side effects for other parts of the system.

Signed-off-by: James Morse <james.morse@....com>
---
 drivers/acpi/acpi_processor.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/acpi_processor.c b/drivers/acpi/acpi_processor.c
index e6419b06cb37..572a12672c0e 100644
--- a/drivers/acpi/acpi_processor.c
+++ b/drivers/acpi/acpi_processor.c
@@ -155,8 +155,10 @@ static int acpi_processor_make_present(struct acpi_processor *pr)
 	acpi_status status;
 	int ret;
 
-	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
+	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU)) {
+		pr_err_once("Changing CPU present bit is not supported\n");
 		return -ENODEV;
+	}
 
 	if (invalid_phys_cpuid(pr->phys_id))
 		return -ENODEV;
@@ -414,8 +416,10 @@ static void acpi_processor_make_not_present(struct acpi_device *device)
 {
 	struct acpi_processor *pr;
 
-	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU))
+	if (!IS_ENABLED(CONFIG_ACPI_HOTPLUG_PRESENT_CPU)) {
+		pr_err_once("Changing CPU present bit is not supported");
 		return;
+	}
 
 	pr = acpi_driver_data(device);
 	if (pr->id >= nr_cpu_ids)
-- 
2.30.2