KVM: Fix load_guest_segment_descriptor() to inject page fault

This patch injects page fault when reading descriptor in
load_guest_segment_descriptor() fails with FAULT.

Effects of this injection: This function is used by
kvm_load_segment_descriptor() which is necessary for the
following instructions:

 - mov seg,r/m16
 - jmp far
 - pop ?s

This patch makes it possible to emulate the page faults
generated by these instructions. But be sure that unless
we change the kvm_load_segment_descriptor()'s ret value
propagation this patch has no effect.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/x86/kvm/x86.c

@@ -4713,16 +4713,23 @@ static int load_guest_segment_descriptor(struct kvm_vcpu *vcpu, u16 selector,
 {
 	struct descriptor_table dtable;
 	u16 index = selector >> 3;
+	int ret;
+	u32 err;
+	gva_t addr;
 
 	get_segment_descriptor_dtable(vcpu, selector, &dtable);
 
 	if (dtable.limit < index * 8 + 7) {
 		kvm_queue_exception_e(vcpu, GP_VECTOR, selector & 0xfffc);
 		return X86EMUL_PROPAGATE_FAULT;
 	}
-	return kvm_read_guest_virt_system(dtable.base + index*8,
-					  seg_desc, sizeof(*seg_desc),
-					  vcpu, NULL);
+	addr = dtable.base + index * 8;
+	ret = kvm_read_guest_virt_system(addr, seg_desc, sizeof(*seg_desc),
+					 vcpu,  &err);
+	if (ret == X86EMUL_PROPAGATE_FAULT)
+		kvm_inject_page_fault(vcpu, addr, err);
+
+       return ret;
 }
 
 /* allowed just for 8 bytes segments */