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>

1 files changed, 48 insertions, 2 deletions

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,