KVM: VMX: Relax check on unusable segment

Some userspace (e.g. QEMU 1.1) munge the d and g bits of segment
descriptors, causing us not to recognize them as unusable segments
with emulate_invalid_guest_state=1.  Relax the check by testing for
segment not present (a non-present segment cannot be usable).

Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 1 insertions, 3 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 486db2f9561..82ab1fb2683 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3198,7 +3198,7 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var)
 {
         u32 ar;
 
-        if (var->unusable)
+        if (var->unusable || !var->present)
                 ar = 1 << 16;
         else {
                 ar = var->type & 15;
@@ -3210,8 +3210,6 @@ static u32 vmx_segment_access_rights(struct kvm_segment *var)
                 ar |= (var->db & 1) << 14;
                 ar |= (var->g & 1) << 15;
         }
-        if (ar == 0) /* a 0 value means unusable */
-                ar = AR_UNUSABLE_MASK;
 
         return ar;
 }