From mboxrd@z Thu Jan  1 00:00:00 1970
From: Scott Wood <scottwood@freescale.com>
Subject: Re: [PATCH 7/7] KVM: PPC: Add userspace debug stub support
Date: Thu, 14 Mar 2013 11:05:30 -0500
Message-ID: <1363277130.28440.3@snotra>
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Cc: Alexander Graf <agraf@suse.de>,
	"kvm-ppc@vger.kernel.org" <kvm-ppc@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Wood Scott-B07421 <B07421@freescale.com>
To: Bhushan Bharat-R65777 <R65777@freescale.com>
Return-path: <kvm-ppc-owner@vger.kernel.org>
In-Reply-To: <6A3DF150A5B70D4F9B66A25E3F7C888D065EC808@039-SN2MPN1-023.039d.mgd.msft.net>
	(from R65777@freescale.com on Thu Mar 14 08:57:53 2013)
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Sender: kvm-ppc-owner@vger.kernel.org
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On 03/14/2013 08:57:53 AM, Bhushan Bharat-R65777 wrote:
> > >>> diff --git a/arch/powerpc/kvm/e500mc.c  
> b/arch/powerpc/kvm/e500mc.c
> > >>> index 1f89d26..f5fc6f5 100644
> > >>> --- a/arch/powerpc/kvm/e500mc.c
> > >>> +++ b/arch/powerpc/kvm/e500mc.c
> > >>> @@ -182,8 +182,7 @@ int kvmppc_core_vcpu_setup(struct kvm_vcpu
> > >>> *vcpu) {
> > >>> 	struct kvmppc_vcpu_e500 *vcpu_e500 = to_e500(vcpu);
> > >>>
> > >>> -	vcpu->arch.shadow_epcr = SPRN_EPCR_DSIGS |  
> SPRN_EPCR_DGTMI | \
> > >>> -				 SPRN_EPCR_DUVD;
> > >>> +	vcpu->arch.shadow_epcr = SPRN_EPCR_DSIGS |  
> SPRN_EPCR_DGTMI;
> > >>
> > >> Doesn't this route all debug events through the host?
> > >
> > > No; This means that debug events can occur in hypervisor state or  
> not.
> > >
> > > EPCR.DUVD = 0 ; Debug events can occur in the hypervisor state.
> > >
> > > EPCR.DUVD = 1 ; Debug events cannot occur in the hypervisor state.
> > >
> > > So we allow debug events to occur in hypervisor state.
> >
> > Why do we care about debug events in our entry/exit code and didn't  
> care about
> > them before?
> 
> We care for single stepping in guest to not step in KVM code.
> 
> > If anything, this is a completely separate patch, orthogonal to
> > this patch series, and requires a good bit of explanation.
> 
> Not sure why you think separate patch; this patch add support for  
> single stepping and also takes care that debug event does not comes  
> in host when doing single stepping.

How does *removing* DUVD ensure that?

-Scott