KVM: PPC: Add userspace debug stub support

This patch adds the debug stub support on booke/bookehv.
Now QEMU debug stub can use hw breakpoint, watchpoint and software
breakpoint to debug guest.

Debug registers are saved/restored on vcpu_put()/vcpu_get().
Also the debug registers are saved restored only if guest
is using debug resources.

Currently we do not support debug resource emulation to guest,
so always exit to user space irrespective of user space is expecting
the debug exception or not. This is unexpected event and let us
leave the action on user space. This is similar to what it was before,
only thing is that now we have proper exit state available to user space.

Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
Signed-off-by: Stuart Yoder <stuart.yoder@freescale.com>

4 files changed, 255 insertions, 22 deletions

diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
index c061e43..6239973 100644
--- a/arch/powerpc/include/asm/kvm_host.h
+++ b/arch/powerpc/include/asm/kvm_host.h
@@ -509,7 +509,15 @@ struct kvm_vcpu_arch {
 	u32 eptcfg;
 	u32 epr;
 	u32 crit_save;
+
+	/* Flag indicating that debug registers are used by guest */
+	bool debug_active;
+	/* for save/restore thread->dbcr0 on vcpu run/heavyweight_exit */
+	u32 saved_dbcr0;
+	/* guest debug registers*/
 	struct kvmppc_booke_debug_reg dbg_reg;
+	/* shadow debug registers */
+	struct kvmppc_booke_debug_reg shadow_dbg_reg;
 #endif
 	gpa_t paddr_accessed;
 	gva_t vaddr_accessed;
diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
index 41d59d8..5aefeb9 100644
--- a/arch/powerpc/include/uapi/asm/kvm.h
+++ b/arch/powerpc/include/uapi/asm/kvm.h
@@ -25,6 +25,7 @@
 /* Select powerpc specific features in <linux/kvm.h> */
 #define __KVM_HAVE_SPAPR_TCE
 #define __KVM_HAVE_PPC_SMT
+#define __KVM_HAVE_GUEST_DEBUG
 
 struct kvm_regs {
 	__u64 pc;
@@ -267,7 +268,24 @@ struct kvm_fpu {
 	__u64 fpr[32];
 };
 
+/*
+ * Defines for h/w breakpoint, watchpoint (read, write or both) and
+ * software breakpoint.
+ * These are used as "type" in KVM_SET_GUEST_DEBUG ioctl and "status"
+ * for KVM_DEBUG_EXIT.
+ */
+#define KVMPPC_DEBUG_NONE		0x0
+#define KVMPPC_DEBUG_BREAKPOINT		(1UL << 1)
+#define KVMPPC_DEBUG_WATCH_WRITE	(1UL << 2)
+#define KVMPPC_DEBUG_WATCH_READ		(1UL << 3)
 struct kvm_debug_exit_arch {
+	__u64 address;
+	/*
+	 * exiting to userspace because of h/w breakpoint, watchpoint
+	 * (read, write or both) and software breakpoint.
+	 */
+	__u32 status;
+	__u32 reserved;
 };
 
 /* for KVM_SET_GUEST_DEBUG */
@@ -279,10 +297,6 @@ struct kvm_guest_debug_arch {
 		 * Type denotes h/w breakpoint, read watchpoint, write
 		 * watchpoint or watchpoint (both read and write).
 		 */
-#define KVMPPC_DEBUG_NONE		0x0
-#define KVMPPC_DEBUG_BREAKPOINT		(1UL << 1)
-#define KVMPPC_DEBUG_WATCH_WRITE	(1UL << 2)
-#define KVMPPC_DEBUG_WATCH_READ		(1UL << 3)
 		__u32 type;
 		__u32 reserved;
 	} bp[16];
diff --git a/arch/powerpc/kvm/booke.c b/arch/powerpc/kvm/booke.c
index ee91cf8..059d7a8 100644
--- a/arch/powerpc/kvm/booke.c
+++ b/arch/powerpc/kvm/booke.c
@@ -133,6 +133,29 @@ static void kvmppc_vcpu_sync_fpu(struct kvm_vcpu *vcpu)
 #endif
 }
 
+static void kvmppc_vcpu_sync_debug(struct kvm_vcpu *vcpu)
+{
+	/* Synchronize guest's desire to get debug interrupts into shadow MSR */
+#ifndef CONFIG_KVM_BOOKE_HV
+	vcpu->arch.shadow_msr &= ~MSR_DE;
+	vcpu->arch.shadow_msr |= vcpu->arch.shared->msr & MSR_DE;
+#endif
+
+	/* Force enable debug interrupts when user space wants to debug */
+	if (vcpu->guest_debug) {
+#ifdef CONFIG_KVM_BOOKE_HV
+		/*
+		 * Since there is no shadow MSR, sync MSR_DE into the guest
+		 * visible MSR.
+		 */
+		vcpu->arch.shared->msr |= MSR_DE;
+#else
+		vcpu->arch.shadow_msr |= MSR_DE;
+		vcpu->arch.shared->msr &= ~MSR_DE;
+#endif
+	}
+}
+
 /*
  * Helper function for "full" MSR writes.  No need to call this if only
  * EE/CE/ME/DE/RI are changing.
@@ -150,6 +173,7 @@ void kvmppc_set_msr(struct kvm_vcpu *vcpu, u32 new_msr)
 	kvmppc_mmu_msr_notify(vcpu, old_msr);
 	kvmppc_vcpu_sync_spe(vcpu);
 	kvmppc_vcpu_sync_fpu(vcpu);
+	kvmppc_vcpu_sync_debug(vcpu);
 }
 
 static void kvmppc_booke_queue_irqprio(struct kvm_vcpu *vcpu,
@@ -646,6 +670,46 @@ int kvmppc_core_check_requests(struct kvm_vcpu *vcpu)
 	return r;
 }
 
+static void kvmppc_load_usespace_gebug(void)
+{
+	switch_booke_debug_regs(&current->thread);
+}
+
+static void kvmppc_booke_vcpu_load_debug_regs(struct kvm_vcpu *vcpu)
+{
+	if (!vcpu->arch.debug_active)
+		return;
+
+	/* Disable all debug events and clead pending debug events */
+	mtspr(SPRN_DBCR0, 0x0);
+	kvmppc_clear_dbsr();
+
+	/*
+	 * Check whether guest still need debug resource, if not then there
+	 * is no need to restore guest context.
+	 */
+	if (!vcpu->arch.shadow_dbg_reg.dbcr0)
+		return;
+
+	/* Load Guest Context */
+	mtspr(SPRN_DBCR1, vcpu->arch.shadow_dbg_reg.dbcr1);
+	mtspr(SPRN_DBCR2, vcpu->arch.shadow_dbg_reg.dbcr2);
+#ifdef CONFIG_KVM_E500MC
+	mtspr(SPRN_DBCR4, vcpu->arch.shadow_dbg_reg.dbcr4);
+#endif
+	mtspr(SPRN_IAC1, vcpu->arch.shadow_dbg_reg.iac[0]);
+	mtspr(SPRN_IAC2, vcpu->arch.shadow_dbg_reg.iac[1]);
+#if CONFIG_PPC_ADV_DEBUG_IACS > 2
+	mtspr(SPRN_IAC3, vcpu->arch.shadow_dbg_reg.iac[2]);
+	mtspr(SPRN_IAC4, vcpu->arch.shadow_dbg_reg.iac[3]);
+#endif
+	mtspr(SPRN_DAC1, vcpu->arch.shadow_dbg_reg.dac[0]);
+	mtspr(SPRN_DAC2, vcpu->arch.shadow_dbg_reg.dac[1]);
+
+	/* Enable debug events after other debug registers restored */
+	mtspr(SPRN_DBCR0, vcpu->arch.shadow_dbg_reg.dbcr0);
+}
+
 int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 {
 	int ret, s;
@@ -693,11 +757,25 @@ int kvmppc_vcpu_run(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu)
 	kvmppc_load_guest_fp(vcpu);
 #endif
 
+	/*
+	 * Clear current->thread.dbcr0 so that kernel does not
+	 * restore h/w registers on context switch in vcpu running state.
+	 */
+	vcpu->arch.debug_active = 1;
+	vcpu->arch.saved_dbcr0 = current->thread.dbcr0;
+	current->thread.dbcr0 = 0;
+	kvmppc_booke_vcpu_load_debug_regs(vcpu);
+
 	ret = __kvmppc_vcpu_run(kvm_run, vcpu);
 
 	/* No need for kvm_guest_exit. It's done in handle_exit.
 	   We also get here with interrupts enabled. */
 
+	/* Restore thread->dbcr0 */
+	vcpu->arch.debug_active = 0;
+	current->thread.dbcr0 = vcpu->arch.saved_dbcr0;
+	kvmppc_load_usespace_gebug();
+
 #ifdef CONFIG_PPC_FPU
 	kvmppc_save_guest_fp(vcpu);
 
@@ -753,6 +831,36 @@ static int emulation_exit(struct kvm_run *run, struct kvm_vcpu *vcpu)
 	}
 }
 
+/*
+ * Currently we do not support debug resource emulation to guest,
+ * so always exit to user space irrespective of user space is
+ * expecting the debug exception or not. This is unexpected event
+ * and let us leave the action on user space.
+ */
+static int kvmppc_handle_debug(struct kvm_run *run, struct kvm_vcpu *vcpu)
+{
+	u32 dbsr = mfspr(SPRN_DBSR);
+
+	kvmppc_clear_dbsr();
+	run->debug.arch.status = 0;
+	run->debug.arch.address = vcpu->arch.pc;
+
+	if (dbsr & (DBSR_IAC1 | DBSR_IAC2 | DBSR_IAC3 | DBSR_IAC4)) {
+		run->debug.arch.status |= KVMPPC_DEBUG_BREAKPOINT;
+	} else {
+		if (dbsr & (DBSR_DAC1W | DBSR_DAC2W))
+			run->debug.arch.status |= KVMPPC_DEBUG_WATCH_WRITE;
+		else if (dbsr & (DBSR_DAC1R | DBSR_DAC2R))
+			run->debug.arch.status |= KVMPPC_DEBUG_WATCH_READ;
+		if (dbsr & (DBSR_DAC1R | DBSR_DAC1W))
+			run->debug.arch.address = vcpu->arch.shadow_dbg_reg.dac[0];
+		else if (dbsr & (DBSR_DAC2R | DBSR_DAC2W))
+			run->debug.arch.address = vcpu->arch.shadow_dbg_reg.dac[1];
+	}
+
+	return RESUME_HOST;
+}
+
 static void kvmppc_fill_pt_regs(struct pt_regs *regs)
 {
 	ulong r1, ip, msr, lr;
@@ -1112,18 +1220,10 @@ int kvmppc_handle_exit(struct kvm_run *run, struct kvm_vcpu *vcpu,
 	}
 
 	case BOOKE_INTERRUPT_DEBUG: {
-		u32 dbsr;
-
-		vcpu->arch.pc = mfspr(SPRN_CSRR0);
-
-		/* clear IAC events in DBSR register */
-		dbsr = mfspr(SPRN_DBSR);
-		dbsr &= DBSR_IAC1 | DBSR_IAC2 | DBSR_IAC3 | DBSR_IAC4;
-		mtspr(SPRN_DBSR, dbsr);
-
-		run->exit_reason = KVM_EXIT_DEBUG;
+		r = kvmppc_handle_debug(run, vcpu);
+		if (r == RESUME_HOST)
+			run->exit_reason = KVM_EXIT_DEBUG;
 		kvmppc_account_exit(vcpu, DEBUG_EXITS);
-		r = RESUME_HOST;
 		break;
 	}
 
@@ -1174,7 +1274,7 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)
 	kvmppc_set_msr(vcpu, 0);
 
 #ifndef CONFIG_KVM_BOOKE_HV
-	vcpu->arch.shadow_msr = MSR_USER | MSR_DE | MSR_IS | MSR_DS;
+	vcpu->arch.shadow_msr = MSR_USER | MSR_IS | MSR_DS;
 	vcpu->arch.shadow_pid = 1;
 	vcpu->arch.shared->msr = 0;
 #endif
@@ -1534,12 +1634,6 @@ int kvm_vcpu_ioctl_set_one_reg(struct kvm_vcpu *vcpu, struct kvm_one_reg *reg)
 	return r;
 }
 
-int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
-					 struct kvm_guest_debug *dbg)
-{
-	return -EINVAL;
-}
-
 int kvm_arch_vcpu_ioctl_get_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 {
 	return -ENOTSUPP;
@@ -1645,16 +1739,128 @@ void kvmppc_decrementer_func(unsigned long data)
 	kvmppc_set_tsr_bits(vcpu, TSR_DIS);
 }
 
+static void kvmppc_booke_vcpu_put_debug_regs(struct kvm_vcpu *vcpu)
+{
+	/* Disable all debug events First */
+	mtspr(SPRN_DBCR0, 0x0);
+	/* Disable pending debug event by clearing DBSR */
+	kvmppc_clear_dbsr();
+}
+
+int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
+					 struct kvm_guest_debug *dbg)
+{
+	struct kvmppc_booke_debug_reg *dbg_reg;
+	int n, b = 0, w = 0;
+	const u32 bp_code[] = {
+		DBCR0_IAC1 | DBCR0_IDM,
+		DBCR0_IAC2 | DBCR0_IDM,
+		DBCR0_IAC3 | DBCR0_IDM,
+		DBCR0_IAC4 | DBCR0_IDM
+	};
+	const u32 wp_code[] = {
+		DBCR0_DAC1W | DBCR0_IDM,
+		DBCR0_DAC2W | DBCR0_IDM,
+		DBCR0_DAC1R | DBCR0_IDM,
+		DBCR0_DAC2R | DBCR0_IDM
+	};
+
+	if (!(dbg->control & KVM_GUESTDBG_ENABLE)) {
+		/* Clear All debug events */
+		vcpu->arch.shadow_dbg_reg.dbcr0 = 0;
+		vcpu->guest_debug = 0;
+#ifdef CONFIG_KVM_BOOKE_HV
+		/*
+		 * When user space is not using the debug resources
+		 * then allow guest to change the MSR.DE.
+		 */
+		vcpu->arch.shadow_msrp &= ~MSRP_DEP;
+#endif
+		return 0;
+	}
+
+#ifdef CONFIG_KVM_BOOKE_HV
+		/*
+		 * When user space is using the debug resource then
+		 * do not allow guest to change the MSR.DE.
+		 */
+		vcpu->arch.shadow_msrp &= ~MSRP_DEP;
+#endif
+	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;
+
+	if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
+		/* Code below handles only HW breakpoints */
+		return 0;
+
+	dbg_reg = &(vcpu->arch.shadow_dbg_reg);
+
+	/*
+	 * On BOOKE (e500v2); Set DBCR1 and DBCR2 to allow debug events
+	 * to occur when MSR.PR is set.
+	 * On BOOKE-HV (e500mc+); MSR.PR = 0 when guest is running. So we
+	 * should clear DBCR1 and DBCR2. And EPCR.DUVD is used to control
+	 * that debug events will not come in hypervisor (GS = 0).
+	 */
+#ifdef CONFIG_KVM_BOOKE_HV
+	dbg_reg->dbcr1 = 0;
+	dbg_reg->dbcr2 = 0;
+#else
+	dbg_reg->dbcr1 = DBCR1_IAC1US | DBCR1_IAC2US | DBCR1_IAC3US |
+			  DBCR1_IAC4US;
+	dbg_reg->dbcr2 = DBCR2_DAC1US | DBCR2_DAC2US;
+#endif
+
+	for (n = 0; n < (KVMPPC_BOOKE_IAC_NUM + KVMPPC_BOOKE_DAC_NUM); n++) {
+		u32 type = dbg->arch.bp[n].type;
+
+		if (!type)
+			continue;
+
+		if (type & (KVMPPC_DEBUG_WATCH_READ |
+			    KVMPPC_DEBUG_WATCH_WRITE)) {
+			if (w >= KVMPPC_BOOKE_DAC_NUM)
+				return -EINVAL;
+
+			if (type & KVMPPC_DEBUG_WATCH_READ)
+				dbg_reg->dbcr0 |= wp_code[w + 2];
+			if (type & KVMPPC_DEBUG_WATCH_WRITE)
+				dbg_reg->dbcr0 |= wp_code[w];
+
+			dbg_reg->dac[w] = dbg->arch.bp[n].addr;
+			w++;
+		} else if (type & KVMPPC_DEBUG_BREAKPOINT) {
+			if (b >= KVMPPC_BOOKE_IAC_NUM)
+				return -EINVAL;
+
+			dbg_reg->dbcr0 |= bp_code[b];
+			dbg_reg->iac[b] = dbg->arch.bp[n].addr;
+			b++;
+		}
+	}
+
+	return 0;
+}
+
 void kvmppc_booke_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 {
 	vcpu->cpu = smp_processor_id();
 	current->thread.kvm_vcpu = vcpu;
+
+	kvmppc_booke_vcpu_load_debug_regs(vcpu);
 }
 
 void kvmppc_booke_vcpu_put(struct kvm_vcpu *vcpu)
 {
 	current->thread.kvm_vcpu = NULL;
 	vcpu->cpu = -1;
+
+	kvmppc_booke_vcpu_put_debug_regs(vcpu);
 }
 
 int __init kvmppc_booke_init(void)
diff --git a/arch/powerpc/kvm/booke.h b/arch/powerpc/kvm/booke.h
index 5fd1ba6..a1ff67d 100644
--- a/arch/powerpc/kvm/booke.h
+++ b/arch/powerpc/kvm/booke.h
@@ -129,4 +129,9 @@ static inline void kvmppc_save_guest_fp(struct kvm_vcpu *vcpu)
 		giveup_fpu(current);
 #endif
 }
+
+static inline void kvmppc_clear_dbsr(void)
+{
+	mtspr(SPRN_DBSR, mfspr(SPRN_DBSR));
+}
 #endif /* __KVM_BOOKE_H__ */