KVM: x86: DR6/7.RTM cannot be written
Haswell and newer Intel CPUs have support for RTM, and in that case DR6.RTM is
not fixed to 1 and DR7.RTM is not fixed to zero. That is not the case in the
current KVM implementation. This bug is apparent only if the MOV-DR instruction
is emulated or the host also debugs the guest.
This patch is a partial fix which enables DR6.RTM and DR7.RTM to be cleared and
set respectively. It also sets DR6.RTM upon every debug exception. Obviously,
it is not a complete fix, as debugging of RTM is still unsupported.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3300f4f..fd24f68 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -4892,7 +4892,7 @@
if (!(vcpu->guest_debug &
(KVM_GUESTDBG_SINGLESTEP | KVM_GUESTDBG_USE_HW_BP))) {
vcpu->arch.dr6 &= ~15;
- vcpu->arch.dr6 |= dr6;
+ vcpu->arch.dr6 |= dr6 | DR6_RTM;
if (!(dr6 & ~DR6_RESERVED)) /* icebp */
skip_emulated_instruction(vcpu);
@@ -5151,7 +5151,7 @@
return 0;
} else {
vcpu->arch.dr7 &= ~DR7_GD;
- vcpu->arch.dr6 |= DR6_BD;
+ vcpu->arch.dr6 |= DR6_BD | DR6_RTM;
vmcs_writel(GUEST_DR7, vcpu->arch.dr7);
kvm_queue_exception(vcpu, DB_VECTOR);
return 1;