linux-kernel - Re: [PATCH 2/2] KVM: make guest mode entry to be rcu quiescent state

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Message-ID: <20110503131317.GA4244@amt.cnet>
Date:	Tue, 3 May 2011 10:13:17 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	linux-kernel@...r.kernel.org, paulmck@...ux.vnet.ibm.com,
	avi@...hat.com, kvm@...r.kernel.org
Subject: Re: [PATCH 2/2] KVM: make guest mode entry to be rcu quiescent state

Hi Gleb,

Thats a neat idea.

On Thu, Apr 28, 2011 at 12:52:03PM +0300, Gleb Natapov wrote:
> KVM does not hold any references to rcu protected data when it switches
> CPU into a guest mode. In fact switching to a guest mode is very similar
> to exiting to userspase from rcu point of view. In addition CPU may stay
> in a guest mode for quite a long time (up to one time slice). Lets treat
> guest mode as quiescent state, just like we do with user-mode execution.
> 
> Signed-off-by: Gleb Natapov <gleb@...hat.com>
> ---
>  include/linux/kvm_host.h |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 0bc3d37..a347bce 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -593,6 +593,7 @@ static inline void kvm_guest_enter(void)
>  {
>  	account_system_vtime(current);
>  	current->flags |= PF_VCPU;
> +	rcu_note_context_switch(smp_processor_id());
>  }
>  
>  static inline void kvm_guest_exit(void)
> -- 
> 1.7.2.3

Please have it in x86's vcpu_enter_guest, then its more explicit
(uncertain about the context of kvm_guest_enter call in other arches).


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