KVM: Load real mode segments correctly

Real mode segments to not reference the GDT or LDT; they simply compute
base = selector * 16.

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

1 files changed, 22 insertions, 0 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 22edd95712ee..bfc7c332c5d7 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3588,11 +3588,33 @@ static int load_segment_descriptor_to_kvm_desct(struct kvm_vcpu *vcpu,
         return 0;
 }
 
+int kvm_load_realmode_segment(struct kvm_vcpu *vcpu, u16 selector, int seg)
+{
+        struct kvm_segment segvar = {
+                .base = selector << 4,
+                .limit = 0xffff,
+                .selector = selector,
+                .type = 3,
+                .present = 1,
+                .dpl = 3,
+                .db = 0,
+                .s = 1,
+                .l = 0,
+                .g = 0,
+                .avl = 0,
+                .unusable = 0,
+        };
+        kvm_x86_ops->set_segment(vcpu, &segvar, seg);
+        return 0;
+}
+
 int kvm_load_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
                                 int type_bits, int seg)
 {
         struct kvm_segment kvm_seg;
 
+        if (!(vcpu->arch.cr0 & X86_CR0_PE))
+                return kvm_load_realmode_segment(vcpu, selector, seg);
         if (load_segment_descriptor_to_kvm_desct(vcpu, selector, &kvm_seg))
                 return 1;
         kvm_seg.type |= type_bits;