> -----Original Message-----
> From: Alexander Graf [mailto:ag...@suse.de]
> Sent: Monday, July 28, 2014 7:35 PM
> To: Bhushan Bharat-R65777; kvm-...@vger.kernel.org
> Cc: kvm@vger.kernel.org; Wood Scott-B07421; Yoder Stuart-B08248
> Subject: Re: [PATCH 6/6] KVM: PPC: BOOKE: Emulate debug registers and 
> exception
> 
> 
> On 11.07.14 10:39, Bharat Bhushan wrote:
> > This patch emulates debug registers and debug exception to support
> > guest using debug resource. This enables running gdb/kgdb etc in
> > guest.
> >
> > On BOOKE architecture we cannot share debug resources between QEMU and
> > guest because:
> >      When QEMU is using debug resources then debug exception must
> >      be always enabled. To achieve this we set MSR_DE and also set
> >      MSRP_DEP so guest cannot change MSR_DE.
> >
> >      When emulating debug resource for guest we want guest
> >      to control MSR_DE (enable/disable debug interrupt on need).
> >
> >      So above mentioned two configuration cannot be supported
> >      at the same time. So the result is that we cannot share
> >      debug resources between QEMU and Guest on BOOKE architecture.
> >
> > In the current design QEMU gets priority over guest, this means that
> > if QEMU is using debug resources then guest cannot use them and if
> > guest is using debug resource then QEMU can overwrite them.
> >
> > Signed-off-by: Bharat Bhushan <bharat.bhus...@freescale.com>
> > ---
> > Hi Alex,
> >
> > I thought of having some print in register emulation if QEMU is using
> > debug resource, Also when QEMU overwrites guest written values but
> > that looks excessive. If I uses some variable which get set when guest
> > starts using debug registers and check in debug set ioctl then that
> > look ugly. Looking for suggestions
> 
> Whatever you do, have QEMU do the print, not the kernel.
> 
> >
> >   arch/powerpc/include/asm/kvm_ppc.h |   3 +
> >   arch/powerpc/kvm/booke.c           |  27 +++++++
> >   arch/powerpc/kvm/booke_emulate.c   | 157
> +++++++++++++++++++++++++++++++++++++
> >   3 files changed, 187 insertions(+)
> >
> > diff --git a/arch/powerpc/include/asm/kvm_ppc.h
> > b/arch/powerpc/include/asm/kvm_ppc.h
> > index e2fd5a1..f3f7611 100644
> > --- a/arch/powerpc/include/asm/kvm_ppc.h
> > +++ b/arch/powerpc/include/asm/kvm_ppc.h
> > @@ -173,6 +173,9 @@ extern int kvmppc_xics_get_xive(struct kvm *kvm, u32 
> > irq,
> u32 *server,
> >   extern int kvmppc_xics_int_on(struct kvm *kvm, u32 irq);
> >   extern int kvmppc_xics_int_off(struct kvm *kvm, u32 irq);
> >
> > +void kvmppc_core_dequeue_debug(struct kvm_vcpu *vcpu); void
> > +kvmppc_core_queue_debug(struct kvm_vcpu *vcpu);
> > +
> >   union kvmppc_one_reg {
> >     u32     wval;
> >     u64     dval;
> > diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c index
> > fadfe76..c2471ed 100644
> > --- a/arch/powerpc/kvm/booke.c
> > +++ b/arch/powerpc/kvm/booke.c
> > @@ -264,6 +264,16 @@ static void kvmppc_core_dequeue_watchdog(struct 
> > kvm_vcpu
> *vcpu)
> >     clear_bit(BOOKE_IRQPRIO_WATCHDOG, &vcpu->arch.pending_exceptions);
> >   }
> >
> > +void kvmppc_core_queue_debug(struct kvm_vcpu *vcpu) {
> > +   kvmppc_booke_queue_irqprio(vcpu, BOOKE_IRQPRIO_DEBUG); }
> > +
> > +void kvmppc_core_dequeue_debug(struct kvm_vcpu *vcpu) {
> > +   clear_bit(BOOKE_IRQPRIO_DEBUG, &vcpu->arch.pending_exceptions); }
> > +
> >   static void set_guest_srr(struct kvm_vcpu *vcpu, unsigned long srr0, u32
> srr1)
> >   {
> >   #ifdef CONFIG_KVM_BOOKE_HV
> > @@ -783,6 +793,23 @@ static int kvmppc_handle_debug(struct kvm_run *run,
> struct kvm_vcpu *vcpu)
> >     struct debug_reg *dbg_reg = &(vcpu->arch.shadow_dbg_reg);
> >     u32 dbsr = vcpu->arch.dbsr;
> >
> > +   if (vcpu->guest_debug == 0) {
> > +           /* Debug resources belong to Guest */
> > +           if (dbsr && (vcpu->arch.shared->msr & MSR_DE))
> > +                   kvmppc_core_queue_debug(vcpu);
> > +
> > +           /* Inject a program interrupt if trap debug is not allowed */
> > +           if ((dbsr & DBSR_TIE) && !(vcpu->arch.shared->msr & MSR_DE))
> > +                   kvmppc_core_queue_program(vcpu, ESR_PTR);
> 
> In that case we would've received a program interrupt and never entered this
> code path, no?

Yes for HV.
But for PR we can be here, MSR_DE is set in h/w msr and guest MSR_DE is not set.
Having a ifdef does not look good but we can have a comment here.

Thanks
-Bharat

> 
> 
> Alex

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