powerpc/kvm: support to handle sw breakpoint

This patch adds kernel side support for software breakpoint.
Design is that, by using an illegal instruction, we trap to hypervisor
via Emulation Assistance interrupt, where we check for the illegal instruction
and accordingly we return to Host or Guest. Patch also adds support for
software breakpoint in PR KVM.
Signed-off-by: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>

arch/powerpc/include/asm/kvm_ppc.h

@@ -38,6 +38,12 @@
 #include <asm/paca.h>
 #endif
 
+/*
+ * KVMPPC_INST_SW_BREAKPOINT is debug Instruction
+ * for supporting software breakpoint.
+ */
+#define KVMPPC_INST_SW_BREAKPOINT	0x00dddd00
+
 enum emulation_result {
 	EMULATE_DONE,         /* no further processing */
 	EMULATE_DO_MMIO,      /* kvm_run filled with MMIO request */

arch/powerpc/kvm/book3s.c

@@ -715,7 +715,8 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
 int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 					struct kvm_guest_debug *dbg)
 {
-	return -EINVAL;
+	vcpu->guest_debug = dbg->control;
+	return 0;
 }
 
 void kvmppc_decrementer_func(struct kvm_vcpu *vcpu)

arch/powerpc/kvm/book3s_hv.c

@@ -725,6 +725,30 @@ static int kvmppc_hcall_impl_hv(unsigned long cmd)
 	return kvmppc_hcall_impl_hv_realmode(cmd);
 }
 
+static int kvmppc_emulate_debug_inst(struct kvm_run *run,
+					struct kvm_vcpu *vcpu)
+{
+	u32 last_inst;
+
+	if (kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst) !=
+					EMULATE_DONE) {
+		/*
+		 * Fetch failed, so return to guest and
+		 * try executing it again.
+		 */
+		return RESUME_GUEST;
+	}
+
+	if (last_inst == KVMPPC_INST_SW_BREAKPOINT) {
+		run->exit_reason = KVM_EXIT_DEBUG;
+		run->debug.arch.address = kvmppc_get_pc(vcpu);
+		return RESUME_HOST;
+	} else {
+		kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
+		return RESUME_GUEST;
+	}
+}
+
 static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
 				 struct task_struct *tsk)
 {
@@ -807,12 +831,18 @@ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu,
 		break;
 	/*
 	 * This occurs if the guest executes an illegal instruction.
-	 * We just generate a program interrupt to the guest, since
-	 * we don't emulate any guest instructions at this stage.
+	 * If the guest debug is disabled, generate a program interrupt
+	 * to the guest. If guest debug is enabled, we need to check
+	 * whether the instruction is a software breakpoint instruction.
+	 * Accordingly return to Guest or Host.
 	 */
 	case BOOK3S_INTERRUPT_H_EMUL_ASSIST:
-		kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
-		r = RESUME_GUEST;
+		if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) {
+			r = kvmppc_emulate_debug_inst(run, vcpu);
+		} else {
+			kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
+			r = RESUME_GUEST;
+		}
 		break;
 	/*
 	 * This occurs if the guest (kernel or userspace), does something that
@@ -924,6 +954,9 @@ static int kvmppc_get_one_reg_hv(struct kvm_vcpu *vcpu, u64 id,
 	long int i;
 
 	switch (id) {
+	case KVM_REG_PPC_DEBUG_INST:
+		*val = get_reg_val(id, KVMPPC_INST_SW_BREAKPOINT);
+		break;
 	case KVM_REG_PPC_HIOR:
 		*val = get_reg_val(id, 0);
 		break;

arch/powerpc/kvm/book3s_pr.c

@@ -1319,6 +1319,9 @@ static int kvmppc_get_one_reg_pr(struct kvm_vcpu *vcpu, u64 id,
 	int r = 0;
 
 	switch (id) {
+	case KVM_REG_PPC_DEBUG_INST:
+		*val = get_reg_val(id, KVMPPC_INST_SW_BREAKPOINT);
+		break;
 	case KVM_REG_PPC_HIOR:
 		*val = get_reg_val(id, to_book3s(vcpu)->hior);
 		break;

arch/powerpc/kvm/emulate.c

@@ -274,6 +274,21 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
 		}
 		break;
 
+	case 0:
+		/*
+		 * Instruction with primary opcode 0. Based on PowerISA
+		 * these are illegal instructions.
+		 */
+		if (inst == KVMPPC_INST_SW_BREAKPOINT) {
+			run->exit_reason = KVM_EXIT_DEBUG;
+			run->debug.arch.address = kvmppc_get_pc(vcpu);
+			emulated = EMULATE_EXIT_USER;
+			advance = 0;
+		} else
+			emulated = EMULATE_FAIL;
+
+		break;
+
 	default:
 		emulated = EMULATE_FAIL;
 	}