From mboxrd@z Thu Jan  1 00:00:00 1970
From: Alexander Graf <agraf@suse.de>
Subject: Re: [PATCH 3/6] KVM: PPC: booke: Check for MSR[WE] in prepare_to_enter
Date: Mon, 14 Nov 2011 14:13:51 +0100
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References: <20111109002325.GC6132@schlenkerla.am.freescale.net>
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Cc: kvm@vger.kernel.org, kvm-ppc@vger.kernel.org
To: Scott Wood <scottwood@freescale.com>
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On 11/09/2011 01:23 AM, Scott Wood wrote:
> This prevents us from inappropriately blocking in a KVM_SET_REGS
> ioctl -- the MSR[WE] will take effect when the guest is next entered.
>
> It also causes SRR1[WE] to be set when we enter the guest's interrupt
> handler, which is what e500 hardware is documented to do.
>
> Signed-off-by: Scott Wood<scottwood@freescale.com>
> ---
>   arch/powerpc/kvm/booke.c |   28 ++++++++++++++++++----------
>   1 files changed, 18 insertions(+), 10 deletions(-)
>
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index feaefc4..557f028 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -124,12 +124,6 @@ void kvmppc_set_msr(struct kvm_vcpu *vcpu, u32 new_msr)
>   	vcpu->arch.shared->msr = new_msr;
>
>   	kvmppc_mmu_msr_notify(vcpu, old_msr);
> -
> -	if (vcpu->arch.shared->msr&  MSR_WE) {
> -		kvm_vcpu_block(vcpu);
> -		kvmppc_set_exit_type(vcpu, EMULATED_MTMSRWE_EXITS);
> -	};
> -
>   	kvmppc_vcpu_sync_spe(vcpu);
>   }
>
> @@ -288,15 +282,12 @@ static int kvmppc_booke_irqprio_deliver(struct kvm_vcpu *vcpu,
>   	return allowed;
>   }
>
> -/* Check pending exceptions and deliver one, if possible. */
> -void kvmppc_core_prepare_to_enter(struct kvm_vcpu *vcpu)
> +static void kvmppc_core_check_exceptions(struct kvm_vcpu *vcpu)
>   {
>   	unsigned long *pending =&vcpu->arch.pending_exceptions;
>   	unsigned long old_pending = vcpu->arch.pending_exceptions;
>   	unsigned int priority;
>
> -	WARN_ON_ONCE(!irqs_disabled());
> -
>   	priority = __ffs(*pending);
>   	while (priority<= BOOKE_IRQPRIO_MAX) {
>   		if (kvmppc_booke_irqprio_deliver(vcpu, priority))
> @@ -314,6 +305,23 @@ void kvmppc_core_prepare_to_enter(struct kvm_vcpu *vcpu)
>   		vcpu->arch.shared->int_pending = 0;
>   }
>
> +/* Check pending exceptions and deliver one, if possible. */
> +void kvmppc_core_prepare_to_enter(struct kvm_vcpu *vcpu)
> +{
> +	WARN_ON_ONCE(!irqs_disabled());
> +
> +	kvmppc_core_check_exceptions(vcpu);
> +
> +	if (vcpu->arch.shared->msr&  MSR_WE) {
> +		local_irq_enable();
> +		kvm_vcpu_block(vcpu);
> +		local_irq_disable();

Hrm. This specific irq enable/disable part isn't pretty but I can't 
think of a cleaner way either. Unless you move it out of the prepare 
function, since I don't see a way it could race with an interrupt.

> +
> +		kvmppc_set_exit_type(vcpu, EMULATED_MTMSRWE_EXITS);
> +		kvmppc_core_check_exceptions(vcpu);

Shouldn't

if (msr & MSR_WE) {
   ...
}

core_check_exceptions(vcpu);


work just as well?