[PATCH v2 3/4] KVM: x86: DR0-DR3 are not clear on reset

[Nadav Amit <namit@cs.technion.ac.il>]

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>
---
 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/x86.c              | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 59f4374..495fcb6 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -345,6 +345,7 @@ 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 c93b1b5..e4ac17e 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;
@@ -6322,6 +6334,7 @@ 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);
@@ -7098,6 +7111,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	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;
-- 
1.9.1