linux-kernel - Re: [PATCH] kvm fix: Enable pvspinlock after jump_label

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Date:	Wed, 09 Oct 2013 11:23:01 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
CC:	mingo@...hat.com, hpa@...or.com, x86@...nel.org, gleb@...hat.com,
	tglx@...utronix.de, konrad.wilk@...cle.com,
	habanero@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, mtosatti@...hat.com,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] kvm fix: Enable pvspinlock after jump_label_init() to
 avoid VM hang

Il 09/10/2013 11:03, Raghavendra K T ha scritto:
> We use jump label to enable pv-spinlock. With the changes in
> (442e0973e927 Merge branch 'x86/jumplabel'), the jump label behaviour has changed
> that would result in evntual hang of the VM since we would end up in a situation
> where slowpath locks would halt the vcpus but we will not be able to wakeup the
> vcpu by lock releaser using unlock kick.
> 
> Similar problem in Xen and more detailed description is available in
> a945928ea270 (xen: Do not enable spinlocks before jump_label_init() has executed)
> 
> This patch splits kvm_spinlock_init to separate jump label changes with pvops
> patching and also make jump label enabling after jump_label_init().
> 
> Signed-off-by: Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
> ---
>  Thanks to Andrew Theurer who reported weird behaviour of pvspinlock
>  in 3.12-rc that led to my git bisection and investigation and Konrad
>  for his jump label findings for Xen.
> 
>  arch/x86/kernel/kvm.c | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 697b93a..a0e2a8a 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -775,11 +775,22 @@ void __init kvm_spinlock_init(void)
>  	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
>  		return;
>  
> -	printk(KERN_INFO "KVM setup paravirtual spinlock\n");
> +	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
> +	pv_lock_ops.unlock_kick = kvm_unlock_kick;
> +}
> +
> +static __init int kvm_spinlock_init_jump(void)
> +{
> +	if (!kvm_para_available())
> +		return 0;
> +	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
> +		return 0;
>  
>  	static_key_slow_inc(&paravirt_ticketlocks_enabled);
> +	printk(KERN_INFO "KVM setup paravirtual spinlock\n");
>  
> -	pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(kvm_lock_spinning);
> -	pv_lock_ops.unlock_kick = kvm_unlock_kick;
> +	return 0;
>  }
> +early_initcall(kvm_spinlock_init_jump);
> +
>  #endif	/* CONFIG_PARAVIRT_SPINLOCKS */
> 

Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
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