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

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Message-ID: <1c852010-e9df-fac8-8970-6c60f769f40e@cn.fujitsu.com>
Date:   Wed, 25 Oct 2017 15:35:21 +0800
From:   Dou Liyang <douly.fnst@...fujitsu.com>
To:     Juergen Gross <jgross@...e.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()

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?

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
>
>
>