linux-kernel - [PATCH v9 15/19] arm64: psci: Ignore DENIED CPUs

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Date: Tue, 30 Apr 2024 15:24:30 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra
	<peterz@...radead.org>, <linux-pm@...r.kernel.org>,
	<loongarch@...ts.linux.dev>, <linux-acpi@...r.kernel.org>,
	<linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <kvmarm@...ts.linux.dev>,
	<x86@...nel.org>, Russell King <linux@...linux.org.uk>, "Rafael J . Wysocki"
	<rafael@...nel.org>, Miguel Luis <miguel.luis@...cle.com>, James Morse
	<james.morse@....com>, Salil Mehta <salil.mehta@...wei.com>, Jean-Philippe
 Brucker <jean-philippe@...aro.org>, Catalin Marinas
	<catalin.marinas@....com>, Will Deacon <will@...nel.org>, Marc Zyngier
	<maz@...nel.org>, Hanjun Guo <guohanjun@...wei.com>, Gavin Shan
	<gshan@...hat.com>
CC: Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave
 Hansen <dave.hansen@...ux.intel.com>, <linuxarm@...wei.com>,
	<justin.he@....com>, <jianyong.wu@....com>
Subject: [PATCH v9 15/19] arm64: psci: Ignore DENIED CPUs

From: Jean-Philippe Brucker <jean-philippe@...aro.org>

When a CPU is marked as disabled, but online capable in the MADT, PSCI
applies some firmware policy to control when it can be brought online.
PSCI returns DENIED to a CPU_ON request if this is not currently
permitted. The OS can learn the current policy from the _STA enabled bit.

Handle the PSCI DENIED return code gracefully instead of printing an
error.

Note the alternatives to the PSCI cpu_boot() callback do not
return -EPERM so the change in smp.c has no affect.

See https://developer.arm.com/documentation/den0022/f/?lang=en page 58.

Signed-off-by: Jean-Philippe Brucker <jean-philippe@...aro.org>
[ morse: Rewrote commit message ]
Signed-off-by: James Morse <james.morse@....com>
Tested-by: Miguel Luis <miguel.luis@...cle.com>
Tested-by: Vishnu Pajjuri <vishnu@...amperecomputing.com>
Tested-by: Jianyong Wu <jianyong.wu@....com>
Reviewed-by: Gavin Shan <gshan@...hat.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
---
v9: Tags picked up
---
 arch/arm64/kernel/psci.c | 2 +-
 arch/arm64/kernel/smp.c  | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
index 29a8e444db83..fabd732d0a2d 100644
--- a/arch/arm64/kernel/psci.c
+++ b/arch/arm64/kernel/psci.c
@@ -40,7 +40,7 @@ static int cpu_psci_cpu_boot(unsigned int cpu)
 {
 	phys_addr_t pa_secondary_entry = __pa_symbol(secondary_entry);
 	int err = psci_ops.cpu_on(cpu_logical_map(cpu), pa_secondary_entry);
-	if (err)
+	if (err && err != -EPERM)
 		pr_err("failed to boot CPU%d (%d)\n", cpu, err);
 
 	return err;
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index afe835c1cbe2..b4b3f832520c 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -132,7 +132,8 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
 	/* Now bring the CPU into our world */
 	ret = boot_secondary(cpu, idle);
 	if (ret) {
-		pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
+		if (ret != -EPERM)
+			pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
 		return ret;
 	}
 
-- 
2.39.2