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

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Message-ID: <132343df-df01-6ab6-bdaf-cd1605028bfc@oderland.se>
Date:   Thu, 11 Nov 2021 13:39:20 +0100
From:   Josef Johansson <josef@...rland.se>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        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 11/11/21 11:15, Peter Zijlstra wrote:
> On Wed, Nov 10, 2021 at 10:52:09PM +0100, Josef Johansson wrote:
>> 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.
> Fixed. Can I add your Tested-by ?
Yes, I tested with tip.

Regards
Josef