linux-kernel - [PATCH RFC 2/4] arm64: kernel: Bound the total(present+disabled) cpus with nr_cpu

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Date:   Thu, 25 Jun 2020 14:37:55 +0100
From:   Salil Mehta <salil.mehta@...wei.com>
To:     <linux-arm-kernel@...ts.infradead.org>
CC:     <maz@...nel.org>, <will@...nel.org>, <catalin.marinas@....com>,
        <christoffer.dall@....com>, <andre.przywara@....com>,
        <james.morse@....com>, <mark.rutland@....com>,
        <lorenzo.pieralisi@....com>, <sudeep.holla@....com>,
        <qemu-arm@...gnu.org>, <peter.maydell@...aro.org>,
        <richard.henderson@...aro.org>, <imammedo@...hat.com>,
        <mst@...hat.com>, <drjones@...hat.com>, <pbonzini@...hat.com>,
        <eric.auger@...hat.com>, <gshan@...hat.com>, <david@...hat.com>,
        <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linuxarm@...wei.com>, <mehta.salil.lnk@...il.com>,
        Salil Mehta <salil.mehta@...wei.com>,
        "Xiongfeng Wang" <wangxiongfeng2@...wei.com>
Subject: [PATCH RFC 2/4] arm64: kernel: Bound the total(present+disabled) cpus with nr_cpu_ids

Bound the total number of identified cpus(including disabled cpus) by
maximum allowed limit by the kernel. Max value is either specified as
part of the kernel parameters 'nr_cpus' or specified during compile
time using CONFIG_NR_CPUS.

Signed-off-by: Salil Mehta <salil.mehta@...wei.com>
Signed-off-by: Xiongfeng Wang <wangxiongfeng2@...wei.com>
---
 arch/arm64/kernel/smp.c | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 51a707928302..864ccd3da419 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -513,6 +513,7 @@ static int __init smp_cpu_setup(int cpu)
 }
 
 static bool bootcpu_valid __initdata;
+static bool cpus_clipped __initdata = false;
 static unsigned int cpu_count = 1;
 static unsigned int disabled_cpu_count;
 
@@ -536,6 +537,11 @@ acpi_map_gic_cpu_interface(struct acpi_madt_generic_interrupt *processor)
 	unsigned int total_cpu_count = disabled_cpu_count + cpu_count;
 	u64 hwid = processor->arm_mpidr;
 
+	if (total_cpu_count > nr_cpu_ids) {
+		cpus_clipped = true;
+		return;
+	}
+
 	if (!(processor->flags & ACPI_MADT_ENABLED)) {
 #ifndef CONFIG_ACPI_HOTPLUG_CPU
 		pr_debug("skipping disabled CPU entry with 0x%llx MPIDR\n", hwid);
@@ -569,9 +575,6 @@ acpi_map_gic_cpu_interface(struct acpi_madt_generic_interrupt *processor)
 		return;
 	}
 
-	if (cpu_count >= NR_CPUS)
-		return;
-
 	/* map the logical cpu id to cpu MPIDR */
 	cpu_logical_map(total_cpu_count) = hwid;
 
@@ -688,8 +691,10 @@ static void __init of_parse_and_init_cpus(void)
 			continue;
 		}
 
-		if (cpu_count >= NR_CPUS)
+		if (cpu_count >= NR_CPUS) {
+			cpus_clipped = true;
 			goto next;
+		}
 
 		pr_debug("cpu logical map 0x%llx\n", hwid);
 		cpu_logical_map(cpu_count) = hwid;
@@ -710,6 +715,7 @@ static void __init of_parse_and_init_cpus(void)
  */
 void __init smp_init_cpus(void)
 {
+	unsigned int total_cpu_count = disabled_cpu_count + cpu_count;
 	int i;
 
 	if (acpi_disabled)
@@ -717,9 +723,9 @@ void __init smp_init_cpus(void)
 	else
 		acpi_parse_and_init_cpus();
 
-	if (cpu_count > nr_cpu_ids)
+	if (cpus_clipped)
 		pr_warn("Number of cores (%d) exceeds configured maximum of %u - clipping\n",
-			cpu_count, nr_cpu_ids);
+			total_cpu_count, nr_cpu_ids);
 
 	if (!bootcpu_valid) {
 		pr_err("missing boot CPU MPIDR, not enabling secondaries\n");
-- 
2.17.1