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

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Date:   Thu, 11 Nov 2021 11:15:55 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josef Johansson <josef@...rland.se>
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 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 ?