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SubjectRe: [v6,3/3] x86/smpboot: Fix __max_logical_packages estimate
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Prarit Bhargava:
> 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@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: Peter Zijlstra <peterz@infradead.org>
>>> Cc: Andi Kleen <ak@linux.intel.com>
>>> Cc: Dave Hansen <dave.hansen@intel.com>
>>> Cc: Piotr Luc <piotr.luc@intel.com>
>>> Cc: Kan Liang <kan.liang@intel.com>
>>> Cc: Borislav Petkov <bp@suse.de>
>>> Cc: Stephane Eranian <eranian@google.com>
>>> Cc: Prarit Bhargava <prarit@redhat.com>
>>> Cc: Arvind Yadav <arvind.yadav.cs@gmail.com>
>>> Cc: Andy Lutomirski <luto@kernel.org>
>>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
>>> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>>> Cc: He Chen <he.chen@linux.intel.com>
>>> Cc: Mathias Krause <minipli@googlemail.com>
>>> Cc: Tim Chen <tim.c.chen@linux.intel.com>
>>> Cc: Vitaly Kuznetsov <vkuznets@redhat.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.

Ok, thanks. If you need some logs, or if I should test something just
ask.

> Does 947134d9b00f
> ("x86/smpboot: Do not use smp_num_siblings in __max_logical_packages
> calculation") help?

No.

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