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    SubjectRe: [v6,3/3] x86/smpboot: Fix __max_logical_packages estimate
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    Date
    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.

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