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Message-ID: <6fdee802-bf24-7fbb-c95a-a6e0d840fbde@redhat.com>
Date: Wed, 7 Feb 2018 14:04:30 -0500
From: Prarit Bhargava <prarit@...hat.com>
To: Simon Gaiser <simon@...isiblethingslab.com>,
xen-devel <xen-devel@...ts.xen.org>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
Peter Zijlstra <peterz@...radead.org>,
Andi Kleen <ak@...ux.intel.com>,
Dave Hansen <dave.hansen@...el.com>,
Piotr Luc <piotr.luc@...el.com>,
Kan Liang <kan.liang@...el.com>, Borislav Petkov <bp@...e.de>,
Stephane Eranian <eranian@...gle.com>,
Arvind Yadav <arvind.yadav.cs@...il.com>,
Andy Lutomirski <luto@...nel.org>,
Christian Borntraeger <borntraeger@...ibm.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
Tom Lendacky <thomas.lendacky@....com>,
He Chen <he.chen@...ux.intel.com>,
Mathias Krause <minipli@...glemail.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [v6,3/3] x86/smpboot: Fix __max_logical_packages estimate
On 02/07/2018 01:44 PM, Simon Gaiser wrote:
> 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.
>>
>> Calculate __max_logical_packages after the cpu enumeration has completed.
>> Use the boot cpu's data to extrapolate the number of packages.
>>
>> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
>> Cc: Thomas Gleixner <tglx@...utronix.de>
>> Cc: Ingo Molnar <mingo@...hat.com>
>> Cc: "H. Peter Anvin" <hpa@...or.com>
>> Cc: x86@...nel.org
>> Cc: Peter Zijlstra <peterz@...radead.org>
>> Cc: Andi Kleen <ak@...ux.intel.com>
>> Cc: Dave Hansen <dave.hansen@...el.com>
>> Cc: Piotr Luc <piotr.luc@...el.com>
>> Cc: Kan Liang <kan.liang@...el.com>
>> Cc: Borislav Petkov <bp@...e.de>
>> Cc: Stephane Eranian <eranian@...gle.com>
>> Cc: Prarit Bhargava <prarit@...hat.com>
>> Cc: Arvind Yadav <arvind.yadav.cs@...il.com>
>> Cc: Andy Lutomirski <luto@...nel.org>
>> Cc: Christian Borntraeger <borntraeger@...ibm.com>
>> Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
>> Cc: Tom Lendacky <thomas.lendacky@....com>
>> Cc: He Chen <he.chen@...ux.intel.com>
>> Cc: Mathias Krause <minipli@...glemail.com>
>> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
>> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
>> ---
>> arch/x86/kernel/smpboot.c | 55 +++++++++--------------------------------------
>> 1 file changed, 10 insertions(+), 45 deletions(-)
>>
>> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
>> index 838d36ff7ba6..2e3c5a394e79 100644
>> --- a/arch/x86/kernel/smpboot.c
>> +++ b/arch/x86/kernel/smpboot.c
>> @@ -308,12 +308,6 @@ int topology_update_package_map(unsigned int pkg, unsigned int cpu)
>> if (new >= 0)
>> goto found;
>>
>> - 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;
>> - }
>> -
>> new = logical_packages++;
>> if (new != pkg)
>> pr_info("CPU %u Converting physical %u to logical package %u\n",
>> @@ -323,44 +317,6 @@ int topology_update_package_map(unsigned int pkg, unsigned int cpu)
>> return 0;
>> }
>>
>> -static void __init smp_init_package_map(struct cpuinfo_x86 *c, unsigned int cpu)
>> -{
>> - unsigned int ncpus;
>> -
>> - /*
>> - * Today neither Intel nor AMD support heterogenous systems. That
>> - * might change in the future....
>> - *
>> - * While ideally we'd want '* smp_num_siblings' in the below @ncpus
>> - * computation, this won't actually work since some Intel BIOSes
>> - * report inconsistent HT data when they disable HT.
>> - *
>> - * In particular, they reduce the APIC-IDs to only include the cores,
>> - * but leave the CPUID topology to say there are (2) siblings.
>> - * This means we don't know how many threads there will be until
>> - * after the APIC enumeration.
>> - *
>> - * By not including this we'll sometimes over-estimate the number of
>> - * logical packages by the amount of !present siblings, but this is
>> - * still better than MAX_LOCAL_APIC.
>> - *
>> - * We use total_cpus not nr_cpu_ids because nr_cpu_ids can be limited
>> - * on the command line leading to a similar issue as the HT disable
>> - * problem because the hyperthreads are usually enumerated after the
>> - * primary cores.
>> - */
>> - ncpus = boot_cpu_data.x86_max_cores;
>> - if (!ncpus) {
>> - pr_warn("x86_max_cores == zero !?!?");
>> - ncpus = 1;
>> - }
>> -
>> - __max_logical_packages = DIV_ROUND_UP(total_cpus, ncpus);
>> - pr_info("Max logical packages: %u\n", __max_logical_packages);
>> -
>> - topology_update_package_map(c->phys_proc_id, cpu);
>> -}
>> -
>> void __init smp_store_boot_cpu_info(void)
>> {
>> int id = 0; /* CPU 0 */
>> @@ -368,7 +324,7 @@ void __init smp_store_boot_cpu_info(void)
>>
>> *c = boot_cpu_data;
>> c->cpu_index = id;
>> - smp_init_package_map(c, id);
>> + topology_update_package_map(c->phys_proc_id, id);
>> cpu_data(id).set = 1;
>> }
>>
>> @@ -1371,7 +1327,16 @@ void __init native_smp_prepare_boot_cpu(void)
>>
>> void __init native_smp_cpus_done(unsigned int max_cpus)
>> {
>> + int ncpus;
>> +
>> pr_debug("Boot done\n");
>> + /*
>> + * Today neither Intel nor AMD support heterogenous systems so
>> + * extrapolate the boot cpu's data to all packages.
>> + */
>> + ncpus = cpu_data(0).booted_cores * smp_num_siblings;
>> + __max_logical_packages = DIV_ROUND_UP(nr_cpu_ids, ncpus);
>> + pr_info("Max logical packages: %u\n", __max_logical_packages);
>>
>> if (x86_has_numa_in_package)
>> set_sched_topology(x86_numa_in_package_topology);
>
> This breaks booting as Xen PV domain for me. The problem seems to be
> that native_smp_cpus_done() is never called on a PV domain. So
> __max_logical_packages is uninitialized and this leads to a NULL
> pointer dereference in coretemp.
>
I'll see if I can figure out a way to test that. Does 947134d9b00f
("x86/smpboot: Do not use smp_num_siblings in __max_logical_packages
calculation") help?
P.
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