[PATCH v6 10/12] KVM: nSVM: Don't assume all active-low bits DR6 are fixed-1

[Sean Christopherson <seanjc@google.com>]

From: Shivansh Dhiman <shivansh.dhiman@amd.com>

When preparing vmcb02 for nested VMRUN, force only the actual fixed-1 bits
instead of setting all active-low bits.  The flaw is currently benign, as
the only active-low bits supported by KVM are RTM (Restricted Transactional
Memory) and BLD (Bus Lock Detect), neither of which is currently supported
on SVM, but that's about to change.

Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
[sean: massage changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/regs.c       | 1 +
 arch/x86/kvm/svm/nested.c | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index 0c76cf17e884..3621f1a47d37 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -784,6 +784,7 @@ unsigned long kvm_get_dr6_fixed_1(struct kvm_vcpu *vcpu)
 
 	return fixed;
 }
+EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_get_dr6_fixed_1);
 
 int kvm_set_dr(struct kvm_vcpu *vcpu, int dr, unsigned long val)
 {
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d3f249cd0f2d..c7a69e309a36 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -808,7 +808,7 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm)
 
 	if (unlikely(new_vmcb12 || vmcb12_is_dirty(control, VMCB_DR))) {
 		vmcb02->save.dr7 = svm->nested.save.dr7 | DR7_FIXED_1;
-		svm->vcpu.arch.dr6  = svm->nested.save.dr6 | DR6_ACTIVE_LOW;
+		svm->vcpu.arch.dr6  = svm->nested.save.dr6 | kvm_get_dr6_fixed_1(vcpu);
 		vmcb_mark_dirty(vmcb02, VMCB_DR);
 	}
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog