[PATCH 2/2 V3] KVM: x86: Emulator should set DR6 upon GD like real CPU

[Tim Gardner]

From: Nadav Amit <namit at cs.technion.ac.il>

BugLink: http://bugs.launchpad.net/bugs/1660519

It should clear B0-B3 and set BD.

Signed-off-by: Nadav Amit <namit at cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
(back ported from commit 6d2a0526b09e551d0f395cfb63e7cb965db825af)
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---

v2 - fixed commit log to indicate clean cherry-pick
v3 - dropped the use of DR6_RTM which had only one
use and no definition.

 arch/x86/kvm/emulate.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f8eea19..23717df 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3533,8 +3533,15 @@ static int check_dr_read(struct x86_emulate_ctxt *ctxt)
 	if ((cr4 & X86_CR4_DE) && (dr == 4 || dr == 5))
 		return emulate_ud(ctxt);
 
-	if (check_dr7_gd(ctxt))
+	if (check_dr7_gd(ctxt)) {
+		ulong dr6;
+
+		ctxt->ops->get_dr(ctxt, 6, &dr6);
+		dr6 &= ~15;
+		dr6 |= DR6_BD;
+		ctxt->ops->set_dr(ctxt, 6, dr6);
 		return emulate_db(ctxt);
+	}
 
 	return X86EMUL_CONTINUE;
 }
-- 
2.7.4