Re: [Xen-devel] [v6, 3/3] x86/smpboot: Fix __max_logical_packages estimate

[Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>]

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@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: x86@xxxxxxxxxx
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
> Cc: Piotr Luc <piotr.luc@xxxxxxxxx>
> Cc: Kan Liang <kan.liang@xxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: Stephane Eranian <eranian@xxxxxxxxxx>
> Cc: Prarit Bhargava <prarit@xxxxxxxxxx>
> Cc: Arvind Yadav <arvind.yadav.cs@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: He Chen <he.chen@xxxxxxxxxxxxxxx>
> Cc: Mathias Krause <minipli@xxxxxxxxxxxxxx>
> Cc: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
>  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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