linux-kernel - Re: [PATCH] x86/smp: Factor out parts of native_smp_prepare

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Date:   Wed, 10 Nov 2021 22:52:09 +0100
From:   Josef Johansson <josef@...rland.se>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, bp@...en8.de, dave.hansen@...ux.intel.com,
        x86@...nel.org, hpa@...or.com, jgross@...e.com
Subject: Re: [PATCH] x86/smp: Factor out parts of native_smp_prepare_cpus()

On 11/3/21 00:36, Boris Ostrovsky wrote:
> Commit 66558b730f25 ("sched: Add cluster scheduler level for x86")
> introduced cpu_l2c_shared_map mask which is expected to be initialized
> by smp_op.smp_prepare_cpus(). That commit only updated
> native_smp_prepare_cpus() version but not xen_pv_smp_prepare_cpus().
> As result Xen PV guests crash in set_cpu_sibling_map().
>
> While the new mask can be allocated in xen_pv_smp_prepare_cpus() one can
> see that both versions of smp_prepare_cpus ops share a number of common
> operations that can be factored out. So do that instead.
>
> Fixes: 66558b730f25 ("sched: Add cluster scheduler level for x86")
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> ---
>  arch/x86/include/asm/smp.h |  1 +
>  arch/x86/kernel/smpboot.c  | 19 +++++++++++++------
>  arch/x86/xen/smp_pv.c      | 11 ++---------
>  3 files changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
> index 08b0e90623ad..81a0211a372d 100644
> --- a/arch/x86/include/asm/smp.h
> +++ b/arch/x86/include/asm/smp.h
> @@ -126,6 +126,7 @@ static inline void arch_send_call_function_ipi_mask(const struct cpumask *mask)
>  
>  void cpu_disable_common(void);
>  void native_smp_prepare_boot_cpu(void);
> +void smp_prepare_cpus_common(void);
>  void native_smp_prepare_cpus(unsigned int max_cpus);
>  void calculate_max_logical_packages(void);
>  void native_smp_cpus_done(unsigned int max_cpus);
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index 8241927addff..d7429198c22f 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1350,12 +1350,7 @@ static void __init smp_get_logical_apicid(void)
>  		cpu0_logical_apicid = GET_APIC_LOGICAL_ID(apic_read(APIC_LDR));
>  }
>  
> -/*
> - * Prepare for SMP bootup.
> - * @max_cpus: configured maximum number of CPUs, It is a legacy parameter
> - *            for common interface support.
> - */
> -void __init native_smp_prepare_cpus(unsigned int max_cpus)
> +void __init smp_prepare_cpus_common(void)
>  {
>  	unsigned int i;
Testing out this patch I got a warning that i is unused. Which it is,
since for_each_possible_cpu(i) is removed.
>  
> @@ -1386,6 +1381,18 @@ void __init native_smp_prepare_cpus(unsigned int max_cpus)
>  	set_sched_topology(x86_topology);
>  
>  	set_cpu_sibling_map(0);
> +}
> +
> +/*
> + * Prepare for SMP bootup.
> + * @max_cpus: configured maximum number of CPUs, It is a legacy parameter
> + *            for common interface support.
> + */
> +void __init native_smp_prepare_cpus(unsigned int max_cpus)
> +{
> +
> +	smp_prepare_cpus_common();
> +
>  	init_freq_invariance(false, false);
>  	smp_sanity_check();
>  
> diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
> index 9e55bcbfcd33..69e91d0d3ca4 100644
> --- a/arch/x86/xen/smp_pv.c
> +++ b/arch/x86/xen/smp_pv.c
> @@ -238,16 +238,9 @@ static void __init xen_pv_smp_prepare_cpus(unsigned int max_cpus)
>  	}
>  	xen_init_lock_cpu(0);
>  
> -	smp_store_boot_cpu_info();
> -	cpu_data(0).x86_max_cores = 1;
> +	smp_prepare_cpus_common();
>  
> -	for_each_possible_cpu(i) {
> -		zalloc_cpumask_var(&per_cpu(cpu_sibling_map, i), GFP_KERNEL);
> -		zalloc_cpumask_var(&per_cpu(cpu_core_map, i), GFP_KERNEL);
> -		zalloc_cpumask_var(&per_cpu(cpu_die_map, i), GFP_KERNEL);
> -		zalloc_cpumask_var(&per_cpu(cpu_llc_shared_map, i), GFP_KERNEL);
> -	}
> -	set_cpu_sibling_map(0);
> +	cpu_data(0).x86_max_cores = 1;
>  
>  	speculative_store_bypass_ht_init();
>