KVM: PPC: BOOKE: Emulate debug registers and exception

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.Bhushan@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

1 files changed, 41 insertions, 1 deletions

diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index 831c1b433b09..b4e81e6be11a 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -335,6 +335,16 @@ 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)
 {
 	kvmppc_set_srr0(vcpu, srr0);
@@ -818,7 +828,32 @@ static int kvmppc_handle_debug(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	struct debug_reg *dbg_reg = &(vcpu->arch.dbg_reg);
 	u32 dbsr = vcpu->arch.dbsr;
 
-	/* Clear guest dbsr (vcpu->arch.dbsr) */
+	if (vcpu->guest_debug == 0) {
+		/*
+		 * Debug resources belong to Guest.
+		 * Imprecise debug event is not injected
+		 */
+		if (dbsr & DBSR_IDE) {
+			dbsr &= ~DBSR_IDE;
+			if (!dbsr)
+				return RESUME_GUEST;
+		}
+
+		if (dbsr && (vcpu->arch.shared->msr & MSR_DE) &&
+			    (vcpu->arch.dbg_reg.dbcr0 & DBCR0_IDM))
+			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);
+
+		return RESUME_GUEST;
+	}
+
+	/*
+	 * Debug resource owned by userspace.
+	 * Clear guest dbsr (vcpu->arch.dbsr)
+	 */
 	vcpu->arch.dbsr = 0;
 	run->debug.arch.status = 0;
 	run->debug.arch.address = vcpu->arch.pc;
@@ -1350,6 +1385,11 @@ int kvmppc_subarch_vcpu_init(struct kvm_vcpu *vcpu)
 	setup_timer(&vcpu->arch.wdt_timer, kvmppc_watchdog_func,
 		    (unsigned long)vcpu);
 
+	/*
+	 * Clear DBSR.MRR to avoid guest debug interrupt as
+	 * this is of host interest
+	 */
+	mtspr(SPRN_DBSR, DBSR_MRR);
 	return 0;
 }