KVM: x86: DR0-DR3 are not clear on reset

DR0-DR3 are not cleared as they should during reset and when they are set from
userspace.  It appears to be caused by c77fb5fe6f03 ("KVM: x86: Allow the guest
to run with dirty debug registers").

Force their reload on these situations.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Message-Id: <1427933438-12782-4-git-send-email-namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

2 files changed, 15 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index d0cfdb08b4c2..9f1d66e2e3b5 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -340,6 +340,7 @@ struct kvm_pmu {
 enum {
         KVM_DEBUGREG_BP_ENABLED = 1,
         KVM_DEBUGREG_WONT_EXIT = 2,
+        KVM_DEBUGREG_RELOAD = 4,
 };
 
 struct kvm_vcpu_arch {
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f7a78c62ab87..ad3809df7d0a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -801,6 +801,17 @@ unsigned long kvm_get_cr8(struct kvm_vcpu *vcpu)
 }
 EXPORT_SYMBOL_GPL(kvm_get_cr8);
 
+static void kvm_update_dr0123(struct kvm_vcpu *vcpu)
+{
+        int i;
+
+        if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP)) {
+                for (i = 0; i < KVM_NR_DB_REGS; i++)
+                        vcpu->arch.eff_db[i] = vcpu->arch.db[i];
+                vcpu->arch.switch_db_regs |= KVM_DEBUGREG_RELOAD;
+        }
+}
+
 static void kvm_update_dr6(struct kvm_vcpu *vcpu)
 {
         if (!(vcpu->guest_debug & KVM_GUESTDBG_USE_HW_BP))
@@ -3150,6 +3161,7 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
                 return -EINVAL;
 
         memcpy(vcpu->arch.db, dbgregs->db, sizeof(vcpu->arch.db));
+        kvm_update_dr0123(vcpu);
         vcpu->arch.dr6 = dbgregs->dr6;
         kvm_update_dr6(vcpu);
         vcpu->arch.dr7 = dbgregs->dr7;
@@ -6323,6 +6335,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
                 set_debugreg(vcpu->arch.eff_db[2], 2);
                 set_debugreg(vcpu->arch.eff_db[3], 3);
                 set_debugreg(vcpu->arch.dr6, 6);
+                vcpu->arch.switch_db_regs &= ~KVM_DEBUGREG_RELOAD;
         }
 
         trace_kvm_entry(vcpu->vcpu_id);
@@ -7104,6 +7117,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu)
         kvm_clear_exception_queue(vcpu);
 
         memset(vcpu->arch.db, 0, sizeof(vcpu->arch.db));
+        kvm_update_dr0123(vcpu);
         vcpu->arch.dr6 = DR6_INIT;
         kvm_update_dr6(vcpu);
         vcpu->arch.dr7 = DR7_FIXED_1;