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

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Date:	Thu, 10 Oct 2013 10:43:43 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
Cc:	<mingo@...hat.com>, <hpa@...or.com>, <x86@...nel.org>,
	<gleb@...hat.com>, <pbonzini@...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>
Subject: Re: [PATCH] kvm fix: Enable pvspinlock after jump_label_init() to
 avoid VM hang

On Wed,  9 Oct 2013 14:33:21 +0530
Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com> wrote:

> 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>

Reviewed-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> ---
>  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(-)
> 
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