KVM: New guest debug interface

This rips out the support for KVM_DEBUG_GUEST and introduces a new IOCTL
instead: KVM_SET_GUEST_DEBUG. The IOCTL payload consists of a generic
part, controlling the "main switch" and the single-step feature. The
arch specific part adds an x86 interface for intercepting both types of
debug exceptions separately and re-injecting them when the host was not
interested. Moveover, the foundation for guest debugging via debug
registers is layed.

To signal breakpoint events properly back to userland, an arch-specific
data block is now returned along KVM_EXIT_DEBUG. For x86, the arch block
contains the PC, the debug exception, and relevant debug registers to
tell debug events properly apart.

The availability of this new interface is signaled by
KVM_CAP_SET_GUEST_DEBUG. Empty stubs for not yet supported archs are
provided.

Note that both SVM and VTX are supported, but only the latter was tested
yet. Based on the experience with all those VTX corner case, I would be
fairly surprised if SVM will work out of the box.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

11 files changed, 138 insertions, 79 deletions

diff --git a/arch/ia64/include/asm/kvm.h b/arch/ia64/include/asm/kvm.h
index bfa86b6af7cd..be3fdb891214 100644
--- a/arch/ia64/include/asm/kvm.h
+++ b/arch/ia64/include/asm/kvm.h
@@ -214,4 +214,11 @@ struct kvm_sregs {
 struct kvm_fpu {
 };
 
+struct kvm_debug_exit_arch {
+};
+
+/* for KVM_SET_GUEST_DEBUG */
+struct kvm_guest_debug_arch {
+};
+
 #endif
diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
index 28f982045f29..de47467a0e61 100644
--- a/arch/ia64/kvm/kvm-ia64.c
+++ b/arch/ia64/kvm/kvm-ia64.c
@@ -1303,8 +1303,8 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
         return -EINVAL;
 }
 
-int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
-                struct kvm_debug_guest *dbg)
+int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
+                                        struct kvm_guest_debug *dbg)
 {
         return -EINVAL;
 }
diff --git a/arch/powerpc/include/asm/kvm.h b/arch/powerpc/include/asm/kvm.h
index f993e4198d5c..755f1b1948c5 100644
--- a/arch/powerpc/include/asm/kvm.h
+++ b/arch/powerpc/include/asm/kvm.h
@@ -52,4 +52,11 @@ struct kvm_fpu {
         __u64 fpr[32];
 };
 
+struct kvm_debug_exit_arch {
+};
+
+/* for KVM_SET_GUEST_DEBUG */
+struct kvm_guest_debug_arch {
+};
+
 #endif /* __LINUX_KVM_POWERPC_H */
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 5f81256287f5..7c2ad4017d6a 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -240,8 +240,8 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
         kvmppc_core_vcpu_put(vcpu);
 }
 
-int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
-                                    struct kvm_debug_guest *dbg)
+int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
+                                        struct kvm_guest_debug *dbg)
 {
         int i;
 
diff --git a/arch/s390/include/asm/kvm.h b/arch/s390/include/asm/kvm.h
index e1f54654e3ae..0b2f829f6d50 100644
--- a/arch/s390/include/asm/kvm.h
+++ b/arch/s390/include/asm/kvm.h
@@ -42,4 +42,11 @@ struct kvm_fpu {
         __u64 fprs[16];
 };
 
+struct kvm_debug_exit_arch {
+};
+
+/* for KVM_SET_GUEST_DEBUG */
+struct kvm_guest_debug_arch {
+};
+
 #endif
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 0d33893e1e89..cbfe91e10120 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -422,8 +422,8 @@ int kvm_arch_vcpu_ioctl_translate(struct kvm_vcpu *vcpu,
         return -EINVAL; /* not implemented yet */
 }
 
-int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
-                                    struct kvm_debug_guest *dbg)
+int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
+                                        struct kvm_guest_debug *dbg)
 {
         return -EINVAL; /* not implemented yet */
 }
diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
index 886c9402ec45..32eb96c7ca27 100644
--- a/arch/x86/include/asm/kvm.h
+++ b/arch/x86/include/asm/kvm.h
@@ -212,6 +212,24 @@ struct kvm_pit_channel_state {
         __s64 count_load_time;
 };
 
+struct kvm_debug_exit_arch {
+        __u32 exception;
+        __u32 pad;
+        __u64 pc;
+        __u64 dr6;
+        __u64 dr7;
+};
+
+#define KVM_GUESTDBG_USE_SW_BP          0x00010000
+#define KVM_GUESTDBG_USE_HW_BP          0x00020000
+#define KVM_GUESTDBG_INJECT_DB          0x00040000
+#define KVM_GUESTDBG_INJECT_BP          0x00080000
+
+/* for KVM_SET_GUEST_DEBUG */
+struct kvm_guest_debug_arch {
+        __u64 debugreg[8];
+};
+
 struct kvm_pit_state {
         struct kvm_pit_channel_state channels[3];
 };
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 53779309514a..c430cd580ee2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -135,12 +135,6 @@ enum {
 
 #define KVM_NR_MEM_OBJS 40
 
-struct kvm_guest_debug {
-        int enabled;
-        unsigned long bp[4];
-        int singlestep;
-};
-
 /*
  * We don't want allocation failures within the mmu code, so we preallocate
  * enough memory for a single page fault in a cache.
@@ -448,8 +442,7 @@ struct kvm_x86_ops {
         void (*vcpu_put)(struct kvm_vcpu *vcpu);
 
         int (*set_guest_debug)(struct kvm_vcpu *vcpu,
-                               struct kvm_debug_guest *dbg);
-        void (*guest_debug_pre)(struct kvm_vcpu *vcpu);
+                               struct kvm_guest_debug *dbg);
         int (*get_msr)(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata);
         int (*set_msr)(struct kvm_vcpu *vcpu, u32 msr_index, u64 data);
         u64 (*get_segment_base)(struct kvm_vcpu *vcpu, int seg);
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 0fbbde54ecae..88d9062f4545 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -968,9 +968,32 @@ static void svm_set_segment(struct kvm_vcpu *vcpu,
 
 }
 
-static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_debug_guest *dbg)
+static int svm_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
 {
-        return -EOPNOTSUPP;
+        int old_debug = vcpu->guest_debug;
+        struct vcpu_svm *svm = to_svm(vcpu);
+
+        vcpu->guest_debug = dbg->control;
+
+        svm->vmcb->control.intercept_exceptions &=
+                ~((1 << DB_VECTOR) | (1 << BP_VECTOR));
+        if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {
+                if (vcpu->guest_debug &
+                    (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
+                        svm->vmcb->control.intercept_exceptions |=
+                                1 << DB_VECTOR;
+                if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
+                        svm->vmcb->control.intercept_exceptions |=
+                                1 << BP_VECTOR;
+        } else
+                vcpu->guest_debug = 0;
+
+        if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+                svm->vmcb->save.rflags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
+        else if (old_debug & KVM_GUESTDBG_SINGLESTEP)
+                svm->vmcb->save.rflags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
+
+        return 0;
 }
 
 static int svm_get_irq(struct kvm_vcpu *vcpu)
@@ -1094,6 +1117,27 @@ static int pf_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
         return kvm_mmu_page_fault(&svm->vcpu, fault_address, error_code);
 }
 
+static int db_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
+{
+        if (!(svm->vcpu.guest_debug &
+              (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))) {
+                kvm_queue_exception(&svm->vcpu, DB_VECTOR);
+                return 1;
+        }
+        kvm_run->exit_reason = KVM_EXIT_DEBUG;
+        kvm_run->debug.arch.pc = svm->vmcb->save.cs.base + svm->vmcb->save.rip;
+        kvm_run->debug.arch.exception = DB_VECTOR;
+        return 0;
+}
+
+static int bp_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
+{
+        kvm_run->exit_reason = KVM_EXIT_DEBUG;
+        kvm_run->debug.arch.pc = svm->vmcb->save.cs.base + svm->vmcb->save.rip;
+        kvm_run->debug.arch.exception = BP_VECTOR;
+        return 0;
+}
+
 static int ud_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 {
         int er;
@@ -2050,6 +2094,8 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm,
         [SVM_EXIT_WRITE_DR3]                    = emulate_on_interception,
         [SVM_EXIT_WRITE_DR5]                    = emulate_on_interception,
         [SVM_EXIT_WRITE_DR7]                    = emulate_on_interception,
+        [SVM_EXIT_EXCP_BASE + DB_VECTOR]        = db_interception,
+        [SVM_EXIT_EXCP_BASE + BP_VECTOR]        = bp_interception,
         [SVM_EXIT_EXCP_BASE + UD_VECTOR]        = ud_interception,
         [SVM_EXIT_EXCP_BASE + PF_VECTOR]        = pf_interception,
         [SVM_EXIT_EXCP_BASE + NM_VECTOR]        = nm_interception,
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1d974c1eaa7d..f55690ddb3ac 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -480,8 +480,13 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
         eb = (1u << PF_VECTOR) | (1u << UD_VECTOR);
         if (!vcpu->fpu_active)
                 eb |= 1u << NM_VECTOR;
-        if (vcpu->guest_debug.enabled)
-                eb |= 1u << DB_VECTOR;
+        if (vcpu->guest_debug & KVM_GUESTDBG_ENABLE) {
+                if (vcpu->guest_debug &
+                    (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
+                        eb |= 1u << DB_VECTOR;
+                if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
+                        eb |= 1u << BP_VECTOR;
+        }
         if (vcpu->arch.rmode.active)
                 eb = ~0;
         if (vm_need_ept())
@@ -1003,40 +1008,23 @@ static void vmx_cache_reg(struct kvm_vcpu *vcpu, enum kvm_reg reg)
         }
 }
 
-static int set_guest_debug(struct kvm_vcpu *vcpu, struct kvm_debug_guest *dbg)
+static int set_guest_debug(struct kvm_vcpu *vcpu, struct kvm_guest_debug *dbg)
 {
-        unsigned long dr7 = 0x400;
-        int old_singlestep;
-
-        old_singlestep = vcpu->guest_debug.singlestep;
-
-        vcpu->guest_debug.enabled = dbg->enabled;
-        if (vcpu->guest_debug.enabled) {
-                int i;
-
-                dr7 |= 0x200;  /* exact */
-                for (i = 0; i < 4; ++i) {
-                        if (!dbg->breakpoints[i].enabled)
-                                continue;
-                        vcpu->guest_debug.bp[i] = dbg->breakpoints[i].address;
-                        dr7 |= 2 << (i*2);    /* global enable */
-                        dr7 |= 0 << (i*4+16); /* execution breakpoint */
-                }
-
-                vcpu->guest_debug.singlestep = dbg->singlestep;
-        } else
-                vcpu->guest_debug.singlestep = 0;
+        int old_debug = vcpu->guest_debug;
+        unsigned long flags;
 
-        if (old_singlestep && !vcpu->guest_debug.singlestep) {
-                unsigned long flags;
+        vcpu->guest_debug = dbg->control;
+        if (!(vcpu->guest_debug & KVM_GUESTDBG_ENABLE))
+                vcpu->guest_debug = 0;
 
-                flags = vmcs_readl(GUEST_RFLAGS);
+        flags = vmcs_readl(GUEST_RFLAGS);
+        if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+                flags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
+        else if (old_debug & KVM_GUESTDBG_SINGLESTEP)
                 flags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
-                vmcs_writel(GUEST_RFLAGS, flags);
-        }
+        vmcs_writel(GUEST_RFLAGS, flags);
 
         update_exception_bitmap(vcpu);
-        vmcs_writel(GUEST_DR7, dr7);
 
         return 0;
 }
@@ -2540,24 +2528,6 @@ static int vmx_set_tss_addr(struct kvm *kvm, unsigned int addr)
         return 0;
 }
 
-static void kvm_guest_debug_pre(struct kvm_vcpu *vcpu)
-{
-        struct kvm_guest_debug *dbg = &vcpu->guest_debug;
-
-        set_debugreg(dbg->bp[0], 0);
-        set_debugreg(dbg->bp[1], 1);
-        set_debugreg(dbg->bp[2], 2);
-        set_debugreg(dbg->bp[3], 3);
-
-        if (dbg->singlestep) {
-                unsigned long flags;
-
-                flags = vmcs_readl(GUEST_RFLAGS);
-                flags |= X86_EFLAGS_TF | X86_EFLAGS_RF;
-                vmcs_writel(GUEST_RFLAGS, flags);
-        }
-}
-
 static int handle_rmode_exception(struct kvm_vcpu *vcpu,
                                   int vec, u32 err_code)
 {
@@ -2574,9 +2544,17 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
          *        the required debugging infrastructure rework.
          */
         switch (vec) {
-        case DE_VECTOR:
         case DB_VECTOR:
+                if (vcpu->guest_debug &
+                    (KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))
+                        return 0;
+                kvm_queue_exception(vcpu, vec);
+                return 1;
         case BP_VECTOR:
+                if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP)
+                        return 0;
+                /* fall through */
+        case DE_VECTOR:
         case OF_VECTOR:
         case BR_VECTOR:
         case UD_VECTOR:
@@ -2593,7 +2571,7 @@ static int handle_rmode_exception(struct kvm_vcpu *vcpu,
 static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
         struct vcpu_vmx *vmx = to_vmx(vcpu);
-        u32 intr_info, error_code;
+        u32 intr_info, ex_no, error_code;
         unsigned long cr2, rip;
         u32 vect_info;
         enum emulation_result er;
@@ -2653,14 +2631,16 @@ static int handle_exception(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                 return 1;
         }
 
-        if ((intr_info & (INTR_INFO_INTR_TYPE_MASK | INTR_INFO_VECTOR_MASK)) ==
-            (INTR_TYPE_HARD_EXCEPTION | 1)) {
+        ex_no = intr_info & INTR_INFO_VECTOR_MASK;
+        if (ex_no == DB_VECTOR || ex_no == BP_VECTOR) {
                 kvm_run->exit_reason = KVM_EXIT_DEBUG;
-                return 0;
+                kvm_run->debug.arch.pc = vmcs_readl(GUEST_CS_BASE) + rip;
+                kvm_run->debug.arch.exception = ex_no;
+        } else {
+                kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
+                kvm_run->ex.exception = ex_no;
+                kvm_run->ex.error_code = error_code;
         }
-        kvm_run->exit_reason = KVM_EXIT_EXCEPTION;
-        kvm_run->ex.exception = intr_info & INTR_INFO_VECTOR_MASK;
-        kvm_run->ex.error_code = error_code;
         return 0;
 }
 
@@ -3600,7 +3580,6 @@ static struct kvm_x86_ops vmx_x86_ops = {
         .vcpu_put = vmx_vcpu_put,
 
         .set_guest_debug = set_guest_debug,
-        .guest_debug_pre = kvm_guest_debug_pre,
         .get_msr = vmx_get_msr,
         .set_msr = vmx_set_msr,
         .get_segment_base = vmx_get_segment_base,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index b5e9932e0f62..e990d164b56d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3005,9 +3005,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
                 goto out;
         }
 
-        if (vcpu->guest_debug.enabled)
-                kvm_x86_ops->guest_debug_pre(vcpu);
-
         vcpu->guest_mode = 1;
         /*
          * Make sure that guest_mode assignment won't happen after
@@ -3218,7 +3215,7 @@ int kvm_arch_vcpu_ioctl_get_regs(struct kvm_vcpu *vcpu, struct kvm_regs *regs)
         /*
          * Don't leak debug flags in case they were set for guest debugging
          */
-        if (vcpu->guest_debug.enabled && vcpu->guest_debug.singlestep)
+        if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
                 regs->rflags &= ~(X86_EFLAGS_TF | X86_EFLAGS_RF);
 
         vcpu_put(vcpu);
@@ -3837,8 +3834,8 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
         return 0;
 }
 
-int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
-                                    struct kvm_debug_guest *dbg)
+int kvm_arch_vcpu_ioctl_set_guest_debug(struct kvm_vcpu *vcpu,
+                                        struct kvm_guest_debug *dbg)
 {
         int r;
 
@@ -3846,6 +3843,11 @@ int kvm_arch_vcpu_ioctl_debug_guest(struct kvm_vcpu *vcpu,
 
         r = kvm_x86_ops->set_guest_debug(vcpu, dbg);
 
+        if (dbg->control & KVM_GUESTDBG_INJECT_DB)
+                kvm_queue_exception(vcpu, DB_VECTOR);
+        else if (dbg->control & KVM_GUESTDBG_INJECT_BP)
+                kvm_queue_exception(vcpu, BP_VECTOR);
+
         vcpu_put(vcpu);
 
         return r;