KVM: x86: emulate sldt and str

These are needed to handle the descriptor table vmexits when emulating
UMIP.

Reviewed-by: Wanpeng Li <wanpeng.li@hotmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -3633,17 +3633,27 @@ static int em_rdmsr(struct x86_emulate_ctxt *ctxt)
 	return X86EMUL_CONTINUE;
 }
 
-static int em_mov_rm_sreg(struct x86_emulate_ctxt *ctxt)
+static int em_store_sreg(struct x86_emulate_ctxt *ctxt, int segment)
 {
-	if (ctxt->modrm_reg > VCPU_SREG_GS)
-		return emulate_ud(ctxt);
+	if (segment > VCPU_SREG_GS &&
+	    (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_UMIP) &&
+	    ctxt->ops->cpl(ctxt) > 0)
+		return emulate_gp(ctxt, 0);
 
-	ctxt->dst.val = get_segment_selector(ctxt, ctxt->modrm_reg);
+	ctxt->dst.val = get_segment_selector(ctxt, segment);
 	if (ctxt->dst.bytes == 4 && ctxt->dst.type == OP_MEM)
 		ctxt->dst.bytes = 2;
 	return X86EMUL_CONTINUE;
 }
 
+static int em_mov_rm_sreg(struct x86_emulate_ctxt *ctxt)
+{
+	if (ctxt->modrm_reg > VCPU_SREG_GS)
+		return emulate_ud(ctxt);
+
+	return em_store_sreg(ctxt, ctxt->modrm_reg);
+}
+
 static int em_mov_sreg_rm(struct x86_emulate_ctxt *ctxt)
 {
 	u16 sel = ctxt->src.val;
@@ -3659,6 +3669,11 @@ static int em_mov_sreg_rm(struct x86_emulate_ctxt *ctxt)
 	return load_segment_descriptor(ctxt, sel, ctxt->modrm_reg);
 }
 
+static int em_sldt(struct x86_emulate_ctxt *ctxt)
+{
+	return em_store_sreg(ctxt, VCPU_SREG_LDTR);
+}
+
 static int em_lldt(struct x86_emulate_ctxt *ctxt)
 {
 	u16 sel = ctxt->src.val;
@@ -3668,6 +3683,11 @@ static int em_lldt(struct x86_emulate_ctxt *ctxt)
 	return load_segment_descriptor(ctxt, sel, VCPU_SREG_LDTR);
 }
 
+static int em_str(struct x86_emulate_ctxt *ctxt)
+{
+	return em_store_sreg(ctxt, VCPU_SREG_TR);
+}
+
 static int em_ltr(struct x86_emulate_ctxt *ctxt)
 {
 	u16 sel = ctxt->src.val;
@@ -4372,8 +4392,8 @@ static const struct opcode group5[] = {
 };
 
 static const struct opcode group6[] = {
-	DI(Prot | DstMem,	sldt),
-	DI(Prot | DstMem,	str),
+	II(Prot | DstMem,	   em_sldt, sldt),
+	II(Prot | DstMem,	   em_str, str),
 	II(Prot | Priv | SrcMem16, em_lldt, lldt),
 	II(Prot | Priv | SrcMem16, em_ltr, ltr),
 	N, N, N, N,