linux-kernel - Re: [PATCH] paravirt/locks: avoid modifying static key before jump_label

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Date:   Wed, 25 Oct 2017 09:51:41 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Dou Liyang <douly.fnst@...fujitsu.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     hpa@...or.com, tglx@...utronix.de, mingo@...hat.com, arnd@...db.de,
        peterz@...radead.org
Subject: Re: [PATCH] paravirt/locks: avoid modifying static key before
 jump_label_init()

On 25/10/17 09:35, Dou Liyang wrote:
> Hi Juergen,
> 
> [...]
>>> I like your original method.
>>> So, I try to fix it by moving the native_pv_lock_init() from
>>>  native_smp_prepare_boot_cpu() to native_smp_prepare_cpus().
>>
>> Hmm, this might work, but the Xen case has to be modified (same for
>> my more general solution), as xen_init_spinlocks() is still modifying
>> the static key too early. And we can't move xen_init_spinlocks() to
>> smp_prepare_cpus() as this would be too late for the alternatives
>> patching.
>>
> 
> Yes, Right.
> 
>> So let me extend your patch a little bit to cover Xen, too.
>>
> 
> Yes!
> 
> How about moving the check of xen_pvspin into native_pv_lock_init()
> like below?

This would leak xen_pvspin to non-Xen code. I'd rather do the
static_branch_disable() in xen_init_lock_cpu() if cpu == 0.


Juergen

> 
> Thanks,
>     dou.
> 
> ------------------------->8
> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> index 041096b..b5f3ecb 100644
> --- a/arch/x86/kernel/paravirt.c
> +++ b/arch/x86/kernel/paravirt.c
> @@ -119,7 +119,7 @@ DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
> 
>  void __init native_pv_lock_init(void)
>  {
> -       if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
> +       if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || !xen_pvspin)
>                 static_branch_disable(&virt_spin_lock_key);
>  }
> 
> diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
> index aed1460..6b1335a 100644
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -1323,6 +1323,8 @@ void __init native_smp_prepare_cpus(unsigned int
> max_cpus)
>         pr_info("CPU0: ");
>         print_cpu_info(&cpu_data(0));
> 
> +       native_pv_lock_init();
> +
>         uv_system_init();
> 
>         set_mtrr_aps_delayed_init();
> @@ -1350,7 +1352,6 @@ void __init native_smp_prepare_boot_cpu(void)
>         /* already set me in cpu_online_mask in boot_cpu_init() */
>         cpumask_set_cpu(me, cpu_callout_mask);
>         cpu_set_state_online(me);
> -       native_pv_lock_init();
>  }
> 
>  void __init native_smp_cpus_done(unsigned int max_cpus)
> diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
> index 5147140..570b2bc 100644
> --- a/arch/x86/xen/smp_pv.c
> +++ b/arch/x86/xen/smp_pv.c
> @@ -236,6 +236,8 @@ static void __init xen_pv_smp_prepare_cpus(unsigned
> int max_cpus)
>                 xen_raw_printk(m);
>                 panic(m);
>         }
> +       native_pv_lock_init();
> +
>         xen_init_lock_cpu(0);
> 
>         smp_store_boot_cpu_info();
> diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
> index e8ab80a..8e0ec79 100644
> --- a/arch/x86/xen/spinlock.c
> +++ b/arch/x86/xen/spinlock.c
> @@ -130,7 +130,6 @@ void __init xen_init_spinlocks(void)
> 
>         if (!xen_pvspin) {
>                 printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
> -               static_branch_disable(&virt_spin_lock_key);
>                 return;
>         }
>         printk(KERN_DEBUG "xen: PV spinlocks enabled\n");
> 
> 
>>> I hope it's useful to you.
>>
>> It really is, thanks.
>>
>>
>> Juergen
>>
>>
>>
> 
> 
>