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

[Simon Gaiser <simon@invisiblethingslab.com>]

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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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