linux-kernel - [PATCH v8 12/16] arm64: psci: Ignore DENIED CPUs

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Date: Fri, 26 Apr 2024 14:51:22 +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>
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>, Lorenzo Pieralisi
	<lpieralisi@...nel.org>, Sudeep Holla <sudeep.holla@....com>
Subject: [PATCH v8 12/16] 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: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@...linux.org.uk>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
---
v8: Note in commit message that the -EPERM guard on the error print
    only affects PSCI as other options never use this error code.
    Should they do so in future, that may well indicate that they
    now support similar refusal to boot.
---
 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 4ced34f62dab..dc0e0b3ec2d4 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