From mboxrd@z Thu Jan  1 00:00:00 1970
From: Scott Wood <scottwood@freescale.com>
Subject: Re: [PATCH 17/38] KVM: PPC: BookE: Add support for vcpu->mode
Date: Tue, 14 Aug 2012 19:17:37 -0500
Message-ID: <502AEAA1.10603@freescale.com>
References: <1344985483-7440-1-git-send-email-agraf@suse.de> <1344985483-7440-18-git-send-email-agraf@suse.de>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Cc: <kvm-ppc@vger.kernel.org>, KVM list <kvm@vger.kernel.org>
To: Alexander Graf <agraf@suse.de>
Return-path: <kvm-ppc-owner@vger.kernel.org>
In-Reply-To: <1344985483-7440-18-git-send-email-agraf@suse.de>
Sender: kvm-ppc-owner@vger.kernel.org
List-Id: kvm.vger.kernel.org

On 08/14/2012 06:04 PM, Alexander Graf wrote:
> Generic KVM code might want to know whether we are inside guest context
> or outside. It also wants to be able to push us out of guest context.
> 
> Add support to the BookE code for the generic vcpu->mode field that describes
> the above states.
> 
> Signed-off-by: Alexander Graf <agraf@suse.de>
> ---
>  arch/powerpc/kvm/booke.c |   11 +++++++++++
>  1 files changed, 11 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index bcf87fe..70a86c0 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -501,6 +501,15 @@ static int kvmppc_prepare_to_enter(struct kvm_vcpu *vcpu)
>  			continue;
>  		}
>  
> +		if (vcpu->mode == EXITING_GUEST_MODE) {
> +			r = 1;
> +			break;
> +		}
> +
> +		/* Going into guest context! Yay! */
> +		vcpu->mode = IN_GUEST_MODE;
> +		smp_wmb();
> +
>  		break;
>  	}

Normally on entry to this function mode should be OUTSIDE_GUEST_MODE,
right?  How could it possibly be EXITING_GUEST_MODE then, since that
only replaces IN_GUEST_MODE?

This doesn't match what x86 does with mode on entry.  Mode is supposed
to be set to IN_GUEST_MODE before requests are checked.

I'm not sure what the point of EXITING_GUEST_MODE is at all, compared to
just waiting until after interrupts are disabled before setting
IN_GUEST_MODE (which we do on ppc, but not on x86 even though it seems
like a trivial change), plus the existing ordering between mode and
requests.

-Scott