[PATCH] x86/smpboot: Fix __max_logical_packages estimate

[PATCH] x86/smpboot: Fix __max_logical_packages estimate

[Prarit Bhargava]

A system booted with a small number of cores enabled per package
panics because the estimate of __max_logical_packages is too low.
This occurs when the total number of active cores across all packages
is less than the maximum core count for a single package.

ie) On a 4 package system with 20 cores/package where only 4 cores
are enabled on each package, the value of __max_logical_packages is
calculated as DIV_ROUND_UP(16 / 20) = 1 and not 4.

Improve the estimate of __max_logical_packages by comparing the current
estimate to the number of SMBIOS type 4 Processor Information structures.
If __max_logical_packages is still insufficient during boot use the largest
possible value of Package ID.

Signed-off-by: Prarit Bhargava <prarit@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Jean Delvare <jdelvare@suse.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Prarit Bhargava <prarit@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
---
 arch/x86/kernel/smpboot.c   | 13 ++++++++++---
 drivers/firmware/dmi_scan.c |  9 +++++++++
 include/linux/dmi.h         |  2 ++
 3 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 54b9e89d4d6b..54c59f3b3d01 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -56,6 +56,7 @@
 #include <linux/stackprotector.h>
 #include <linux/gfp.h>
 #include <linux/cpuidle.h>
+#include <linux/dmi.h>
 
 #include <asm/acpi.h>
 #include <asm/desc.h>
@@ -298,7 +299,10 @@ int topology_update_package_map(unsigned int pkg, unsigned int cpu)
 	if (logical_packages >= __max_logical_packages) {
 		pr_warn("Package %u of CPU %u exceeds BIOS package data %u.\n",
 			logical_packages, cpu, __max_logical_packages);
-		return -ENOSPC;
+		if (system_state == SYSTEM_BOOTING)
+			__max_logical_packages = max_physical_pkg_id;
+		else
+			return -ENOSPC;
 	}
 
 	new = logical_packages++;
@@ -332,6 +336,8 @@ static void __init smp_init_package_map(struct cpuinfo_x86 *c, unsigned int cpu)
 	size_t size;
 
 	/*
+	 * Estimate the number of logical packages.
+	 *
 	 * Today neither Intel nor AMD support heterogenous systems. That
 	 * might change in the future....
 	 *
@@ -360,6 +366,8 @@ static void __init smp_init_package_map(struct cpuinfo_x86 *c, unsigned int cpu)
 	}
 
 	__max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
+	__max_logical_packages = max_t(unsigned int, __max_logical_packages,
+				       dmi_processor_count);
 	logical_packages = 0;
 
 	/*
@@ -373,9 +381,8 @@ static void __init smp_init_package_map(struct cpuinfo_x86 *c, unsigned int cpu)
 	size = BITS_TO_LONGS(max_physical_pkg_id) * sizeof(unsigned long);
 	physical_package_map = kzalloc(size, GFP_KERNEL);
 
-	pr_info("Max logical packages: %u\n", __max_logical_packages);
-
 	topology_update_package_map(c->phys_proc_id, cpu);
+	pr_info("Max logical packages: %u\n", __max_logical_packages);
 }
 
 void __init smp_store_boot_cpu_info(void)
diff --git a/drivers/firmware/dmi_scan.c b/drivers/firmware/dmi_scan.c
index 783041964439..177a571e6776 100644
--- a/drivers/firmware/dmi_scan.c
+++ b/drivers/firmware/dmi_scan.c
@@ -420,6 +420,12 @@ void __init dmi_memdev_walk(void)
 	}
 }
 
+unsigned int dmi_processor_count;
+void __init dmi_save_processor(const struct dmi_header *dm)
+{
+	dmi_processor_count++;
+}
+
 /*
  *	Process a DMI table entry. Right now all we care about are the BIOS
  *	and machine entries. For 2.5 we should pull the smbus controller info
@@ -455,6 +461,9 @@ static void __init dmi_decode(const struct dmi_header *dm, void *dummy)
 		dmi_save_ident(dm, DMI_CHASSIS_SERIAL, 7);
 		dmi_save_ident(dm, DMI_CHASSIS_ASSET_TAG, 8);
 		break;
+	case 4:		/* Processor Information */
+		dmi_save_processor(dm);
+		break;
 	case 9:		/* System Slots */
 		dmi_save_system_slot(dm);
 		break;
diff --git a/include/linux/dmi.h b/include/linux/dmi.h
index 9bbf21a516e4..c03f6a5d55f7 100644
--- a/include/linux/dmi.h
+++ b/include/linux/dmi.h
@@ -112,6 +112,7 @@ extern int dmi_walk(void (*decode)(const struct dmi_header *, void *),
 	void *private_data);
 extern bool dmi_match(enum dmi_field f, const char *str);
 extern void dmi_memdev_name(u16 handle, const char **bank, const char **device);
+extern unsigned int dmi_processor_count;
 
 #else
 
@@ -143,6 +144,7 @@ static inline void dmi_memdev_name(u16 handle, const char **bank,
 		const char **device) { }
 static inline const struct dmi_system_id *
 	dmi_first_match(const struct dmi_system_id *list) { return NULL; }
+static unsigned int dmi_processor_count;
 
 #endif
 
-- 
1.8.5.5

Re: [PATCH] x86/smpboot: Fix __max_logical_packages estimate

[Prarit Bhargava]

On 09/06/2017 02:36 PM, Prarit Bhargava wrote:
> A system booted with a small number of cores enabled per package
> panics because the estimate of __max_logical_packages is too low.
> This occurs when the total number of active cores across all packages
> is less than the maximum core count for a single package.
> 
> ie) On a 4 package system with 20 cores/package where only 4 cores
> are enabled on each package, the value of __max_logical_packages is
> calculated as DIV_ROUND_UP(16 / 20) = 1 and not 4.
> 
> Improve the estimate of __max_logical_packages by comparing the current
> estimate to the number of SMBIOS type 4 Processor Information structures.
> If __max_logical_packages is still insufficient during boot use the largest
> possible value of Package ID.

If I move this calculation to native_smp_cpus_done() I can eliminate a chunk
of code and use boot_cpu_data.booted_cores to get a correct value.

I'll resubmit with a new patch.

P.