Re: [PATCH 1/6] KVM: PPC: BOOKE: No need to set DBCR0_EDM in guest visible register

[Scott Wood <scottwood@freescale.com>]

On Fri, 2014-07-11 at 14:08 +0530, Bharat Bhushan wrote:
> This is not used and  even I do not remember why this was added
> in first place.
> 
> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@freescale.com>
> ---
>  arch/powerpc/kvm/booke.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
> index ab62109..a5ee42c 100644
> --- a/arch/powerpc/kvm/booke.c
> +++ b/arch/powerpc/kvm/booke.c
> @@ -1804,8 +1804,6 @@ int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
>  	kvm_guest_protect_msr(vcpu, MSR_DE, true);
>  	vcpu->guest_debug = dbg->control;
>  	vcpu->arch.shadow_dbg_reg.dbcr0 = 0;
> -	/* Set DBCR0_EDM in guest visible DBCR0 register. */
> -	vcpu->arch.dbg_reg.dbcr0 = DBCR0_EDM;
>  
>  	if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
>  		vcpu->arch.shadow_dbg_reg.dbcr0 |= DBCR0_IDM | DBCR0_IC;

This was intended to let the guest know that the host owns the debug
resources, by analogy to what a JTAG debugger would do.

The Power ISA has this "Virtualized Implementation Note":

        It is the responsibility of the hypervisor to ensure that
        DBCR0[EDM] is consistent with usage of DEP.

-Scott