KVM: s390: hardware support for guest debugging

This patch adds support to debug the guest using the PER facility on s390.
Single-stepping, hardware breakpoints and hardware watchpoints are supported. In
order to use the PER facility of the guest without it noticing it, the control
registers of the guest have to be patched and access to them has to be
intercepted(stctl, stctg, lctl, lctlg).

All PER program interrupts have to be intercepted and only the relevant PER
interrupts for the guest have to be given back. Special care has to be taken
about repeated exits on the same hardware breakpoint. The intervention of the
host in the guests PER configuration is not fully transparent. PER instruction
nullification can not be used by the guest and too many storage alteration
events may be reported to the guest (if it is activated for special address
ranges only) when the host concurrently debugging it.
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/include/asm/kvm_host.h

@@ -93,10 +93,15 @@ struct kvm_s390_sie_block {
 	__u8	reserved40[4];		/* 0x0040 */
 #define LCTL_CR0	0x8000
 #define LCTL_CR6	0x0200
+#define LCTL_CR9	0x0040
+#define LCTL_CR10	0x0020
+#define LCTL_CR11	0x0010
 #define LCTL_CR14	0x0002
 	__u16   lctl;			/* 0x0044 */
 	__s16	icpua;			/* 0x0046 */
+#define ICTL_PINT	0x20000000
 #define ICTL_LPSW	0x00400000
+#define ICTL_STCTL	0x00040000
 #define ICTL_ISKE	0x00004000
 #define ICTL_SSKE	0x00002000
 #define ICTL_RRBE	0x00001000
@@ -306,6 +311,45 @@ struct kvm_s390_float_interrupt {
 	unsigned int irq_count;
 };
 
+struct kvm_hw_wp_info_arch {
+	unsigned long addr;
+	unsigned long phys_addr;
+	int len;
+	char *old_data;
+};
+
+struct kvm_hw_bp_info_arch {
+	unsigned long addr;
+	int len;
+};
+
+/*
+ * Only the upper 16 bits of kvm_guest_debug->control are arch specific.
+ * Further KVM_GUESTDBG flags which an be used from userspace can be found in
+ * arch/s390/include/uapi/asm/kvm.h
+ */
+#define KVM_GUESTDBG_EXIT_PENDING 0x10000000
+
+#define guestdbg_enabled(vcpu) \
+		(vcpu->guest_debug & KVM_GUESTDBG_ENABLE)
+#define guestdbg_sstep_enabled(vcpu) \
+		(vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+#define guestdbg_hw_bp_enabled(vcpu) \
+		(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)
+#define guestdbg_exit_pending(vcpu) (guestdbg_enabled(vcpu) && \
+		(vcpu->guest_debug & KVM_GUESTDBG_EXIT_PENDING))
+
+struct kvm_guestdbg_info_arch {
+	unsigned long cr0;
+	unsigned long cr9;
+	unsigned long cr10;
+	unsigned long cr11;
+	struct kvm_hw_bp_info_arch *hw_bp_info;
+	struct kvm_hw_wp_info_arch *hw_wp_info;
+	int nr_hw_bp;
+	int nr_hw_wp;
+	unsigned long last_bp;
+};
 
 struct kvm_vcpu_arch {
 	struct kvm_s390_sie_block *sie_block;
@@ -321,6 +365,7 @@ struct kvm_vcpu_arch {
 		u64		stidp_data;
 	};
 	struct gmap *gmap;
+	struct kvm_guestdbg_info_arch guestdbg;
 #define KVM_S390_PFAULT_TOKEN_INVALID	(-1UL)
 	unsigned long pfault_token;
 	unsigned long pfault_select;

arch/s390/include/uapi/asm/kvm.h

@@ -15,6 +15,7 @@
 #include <linux/types.h>
 
 #define __KVM_S390
+#define __KVM_HAVE_GUEST_DEBUG
 
 /* Device control API: s390-specific devices */
 #define KVM_DEV_FLIC_GET_ALL_IRQS	1

arch/s390/kvm/Makefile

@@ -12,6 +12,6 @@ common-objs = $(KVM)/kvm_main.o $(KVM)/eventfd.o  $(KVM)/async_pf.o $(KVM)/irqch
 ccflags-y := -Ivirt/kvm -Iarch/s390/kvm
 
 kvm-objs := $(common-objs) kvm-s390.o intercept.o interrupt.o priv.o sigp.o
-kvm-objs += diag.o gaccess.o
+kvm-objs += diag.o gaccess.o guestdbg.o
 
 obj-$(CONFIG_KVM) += kvm.o

arch/s390/kvm/intercept.c

@@ -170,6 +170,8 @@ static void __extract_prog_irq(struct kvm_vcpu *vcpu,
 	}
 }
 
+#define per_event(vcpu) (vcpu->arch.sie_block->iprcc & PGM_PER)
+
 static int handle_prog(struct kvm_vcpu *vcpu)
 {
 	struct kvm_s390_pgm_info pgm_info;
@@ -178,6 +180,13 @@ static int handle_prog(struct kvm_vcpu *vcpu)
 
 	vcpu->stat.exit_program_interruption++;
 
+	if (guestdbg_enabled(vcpu) && per_event(vcpu)) {
+		kvm_s390_handle_per_event(vcpu);
+		/* the interrupt might have been filtered out completely */
+		if (vcpu->arch.sie_block->iprcc == 0)
+			return 0;
+	}
+
 	/* Restore ITDB to Program-Interruption TDB in guest memory */
 	if (!IS_TE_ENABLED(vcpu) || !IS_ITDB_VALID(vcpu))
 		goto skip_itdb;

arch/s390/kvm/interrupt.c

@@ -131,7 +131,13 @@ static void __reset_intercept_indicators(struct kvm_vcpu *vcpu)
 		CPUSTAT_IO_INT | CPUSTAT_EXT_INT | CPUSTAT_STOP_INT,
 		&vcpu->arch.sie_block->cpuflags);
 	vcpu->arch.sie_block->lctl = 0x0000;
-	vcpu->arch.sie_block->ictl &= ~ICTL_LPSW;
+	vcpu->arch.sie_block->ictl &= ~(ICTL_LPSW | ICTL_STCTL | ICTL_PINT);
+
+	if (guestdbg_enabled(vcpu)) {
+		vcpu->arch.sie_block->lctl |= (LCTL_CR0 | LCTL_CR9 |
+					       LCTL_CR10 | LCTL_CR11);
+		vcpu->arch.sie_block->ictl |= (ICTL_STCTL | ICTL_PINT);
+	}
 }
 
 static void __set_cpuflag(struct kvm_vcpu *vcpu, u32 flag)

arch/s390/kvm/kvm-s390.c

@@ -934,10 +934,40 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
 	return -EINVAL; /* not implemented yet */
 }
 
+#define VALID_GUESTDBG_FLAGS (KVM_GUESTDBG_SINGLESTEP | \
+			      KVM_GUESTDBG_USE_HW_BP | \
+			      KVM_GUESTDBG_ENABLE)
+
 int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
 					struct kvm_guest_debug *dbg)
 {
-	return -EINVAL; /* not implemented yet */
+	int rc = 0;
+
+	vcpu->guest_debug = 0;
+	kvm_s390_clear_bp_data(vcpu);
+
+	if (vcpu->guest_debug & ~VALID_GUESTDBG_FLAGS)
+		return -EINVAL;
+
+	if (dbg->control & KVM_GUESTDBG_ENABLE) {
+		vcpu->guest_debug = dbg->control;
+		/* enforce guest PER */
+		atomic_set_mask(CPUSTAT_P, &vcpu->arch.sie_block->cpuflags);
+
+		if (dbg->control & KVM_GUESTDBG_USE_HW_BP)
+			rc = kvm_s390_import_bp_data(vcpu, dbg);
+	} else {
+		atomic_clear_mask(CPUSTAT_P, &vcpu->arch.sie_block->cpuflags);
+		vcpu->arch.guestdbg.last_bp = 0;
+	}
+
+	if (rc) {
+		vcpu->guest_debug = 0;
+		kvm_s390_clear_bp_data(vcpu);
+		atomic_clear_mask(CPUSTAT_P, &vcpu->arch.sie_block->cpuflags);
+	}
+
+	return rc;
 }
 
 int kvm_arch_vcpu_ioctl_get_mpstate(struct kvm_vcpu *vcpu,
@@ -1095,6 +1125,11 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu)
 	if (rc)
 		return rc;
 
+	if (guestdbg_enabled(vcpu)) {
+		kvm_s390_backup_guest_per_regs(vcpu);
+		kvm_s390_patch_guest_per_regs(vcpu);
+	}
+
 	vcpu->arch.sie_block->icptcode = 0;
 	cpuflags = atomic_read(&vcpu->arch.sie_block->cpuflags);
 	VCPU_EVENT(vcpu, 6, "entering sie flags %x", cpuflags);
@@ -1111,6 +1146,9 @@ static int vcpu_post_run(struct kvm_vcpu *vcpu, int exit_reason)
 		   vcpu->arch.sie_block->icptcode);
 	trace_kvm_s390_sie_exit(vcpu, vcpu->arch.sie_block->icptcode);
 
+	if (guestdbg_enabled(vcpu))
+		kvm_s390_restore_guest_per_regs(vcpu);
+
 	if (exit_reason >= 0) {
 		rc = 0;
 	} else if (kvm_is_ucontrol(vcpu->kvm)) {
@@ -1176,7 +1214,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu)
 		vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
 
 		rc = vcpu_post_run(vcpu, exit_reason);
-	} while (!signal_pending(current) && !rc);
+	} while (!signal_pending(current) && !guestdbg_exit_pending(vcpu) && !rc);
 
 	srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
 	return rc;
@@ -1187,6 +1225,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	int rc;
 	sigset_t sigsaved;
 
+	if (guestdbg_exit_pending(vcpu)) {
+		kvm_s390_prepare_debug_exit(vcpu);
+		return 0;
+	}
+
 	if (vcpu->sigset_active)
 		sigprocmask(SIG_SETMASK, &vcpu->sigset, &sigsaved);
 
@@ -1199,6 +1242,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 	case KVM_EXIT_S390_RESET:
 	case KVM_EXIT_S390_UCONTROL:
 	case KVM_EXIT_S390_TSCH:
+	case KVM_EXIT_DEBUG:
 		break;
 	default:
 		BUG();
@@ -1224,6 +1268,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 		rc = -EINTR;
 	}
 
+	if (guestdbg_exit_pending(vcpu) && !rc)  {
+		kvm_s390_prepare_debug_exit(vcpu);
+		rc = 0;
+	}
+
 	if (rc == -EOPNOTSUPP) {
 		/* intercept cannot be handled in-kernel, prepare kvm-run */
 		kvm_run->exit_reason         = KVM_EXIT_S390_SIEIC;

arch/s390/kvm/kvm-s390.h

@@ -211,4 +211,14 @@ int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
 int psw_extint_disabled(struct kvm_vcpu *vcpu);
 void kvm_s390_destroy_adapters(struct kvm *kvm);
 
+/* implemented in guestdbg.c */
+void kvm_s390_backup_guest_per_regs(struct kvm_vcpu *vcpu);
+void kvm_s390_restore_guest_per_regs(struct kvm_vcpu *vcpu);
+void kvm_s390_patch_guest_per_regs(struct kvm_vcpu *vcpu);
+int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
+			    struct kvm_guest_debug *dbg);
+void kvm_s390_clear_bp_data(struct kvm_vcpu *vcpu);
+void kvm_s390_prepare_debug_exit(struct kvm_vcpu *vcpu);
+void kvm_s390_handle_per_event(struct kvm_vcpu *vcpu);
+
 #endif