[PATCH 2/3] KVM: x86: handle hardware breakpoints during emulation

Paolo Bonzini
2013-07-30T15:12:16Z

This lets debugging work better during emulation of invalid
guest state.

The check is done before emulating the instruction, and (in the case
of guest debugging) reuses EMULATE_DO_MMIO to exit with KVM_EXIT_DEBUG.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/x86.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 66 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c2a0674..1368cf5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4956,6 +4956,62 @@ static bool retry_instruction(struct x86_emulate_ctxt *ctxt,
static int complete_emulated_mmio(struct kvm_vcpu *vcpu);
static int complete_emulated_pio(struct kvm_vcpu *vcpu);

+static int kvm_vcpu_check_hw_bp(unsigned long addr, u32 type, u32 dr7,
+ unsigned long *db)
+{
+ u32 dr6 = 0;
+ int i;
+ u32 enable, rwlen;
+
+ enable = dr7;
+ rwlen = dr7 >> 16;
+ for (i = 0; i < 4; i++, enable >>= 2, rwlen >>= 4)
+ if ((enable & 3) && (rwlen & 15) == type && db[i] == addr)
+ dr6 |= (1 << i);
+ return dr6;
+}
+
+static bool kvm_vcpu_check_breakpoint(struct kvm_vcpu *vcpu, int *r)
+{
+ struct kvm_run *kvm_run = vcpu->run;
+ unsigned long eip = vcpu->arch.emulate_ctxt.eip;
+ u32 dr6 = 0;
+
+ if (unlikely(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP) &&
+ (vcpu->arch.guest_debug_dr7 & DR7_BP_EN_MASK)) {
+ dr6 = kvm_vcpu_check_hw_bp(eip, 0,
+ vcpu->arch.guest_debug_dr7,
+ vcpu->arch.eff_db);
+
+ if (dr6 != 0) {
+ kvm_run->debug.arch.dr6 = dr6 | DR6_FIXED_1;
+ kvm_run->debug.arch.pc = kvm_rip_read(vcpu) +
+ get_segment_base(vcpu, VCPU_SREG_CS);
+
+ kvm_run->debug.arch.exception = DB_VECTOR;
+ kvm_run->exit_reason = KVM_EXIT_DEBUG;
+ *r = EMULATE_USER_EXIT;
+ return true;
+ }
+ }
+
+ if (unlikely(vcpu->arch.dr7 & DR7_BP_EN_MASK)) {
+ dr6 = kvm_vcpu_check_hw_bp(eip, 0,
+ vcpu->arch.dr7,
+ vcpu->arch.db);
+
+ if (dr6 != 0) {
+ vcpu->arch.dr6 &= ~15;
+ vcpu->arch.dr6 |= dr6;
+ kvm_queue_exception(vcpu, DB_VECTOR);
+ *r = EMULATE_DONE;
+ return true;
+ }
+ }
+
+ return false;
+}
+
int x86_emulate_instruction(struct kvm_vcpu *vcpu,
unsigned long cr2,
int emulation_type,
@@ -4976,6 +5032,16 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,

if (!(emulation_type & EMULTYPE_NO_DECODE)) {
init_emulate_ctxt(vcpu);
+
+ /*
+ * We will reenter on the same instruction since
+ * we do not set complete_userspace_io. This does not
+ * handle watchpoints yet, those would be handled in
+ * the emulate_ops.
+ */
+ if (kvm_vcpu_check_breakpoint(vcpu, &r))
+ return r;
+
ctxt->interruptibility = 0;
ctxt->have_exception = false;
ctxt->perm_ok = false;
--
1.8.1.4