KVM: VMX: when entering real mode align segment base to 16 bytes

VMX checks that base is equal segment shifted 4 bits left. Otherwise
guest entry fails.
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/vmx.c

@@ -1736,9 +1736,13 @@ static void fix_rmode_seg(int seg, struct kvm_save_segment *save)
 	save->limit = vmcs_read32(sf->limit);
 	save->ar = vmcs_read32(sf->ar_bytes);
 	vmcs_write16(sf->selector, save->base >> 4);
-	vmcs_write32(sf->base, save->base & 0xfffff);
+	vmcs_write32(sf->base, save->base & 0xffff0);
 	vmcs_write32(sf->limit, 0xffff);
 	vmcs_write32(sf->ar_bytes, 0xf3);
+	if (save->base & 0xf)
+		printk_once(KERN_WARNING "kvm: segment base is not paragraph"
+			    " aligned when entering protected mode (seg=%d)",
+			    seg);
 }
 
 static void enter_rmode(struct kvm_vcpu *vcpu)