KVM: X86: avoid unused setup_syscalls_segments call when SYSCALL check failed

When SYSCALL/SYSENTER ability check failed, cs and ss is inited but
remain not used. Delay initializing cs and ss until SYSCALL/SYSENTER
ability check passed.
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/emulate.c

@@ -2770,11 +2770,10 @@ static int em_syscall(struct x86_emulate_ctxt *ctxt)
 		return emulate_ud(ctxt);
 
 	ops->get_msr(ctxt, MSR_EFER, &efer);
-	setup_syscalls_segments(ctxt, &cs, &ss);
-
 	if (!(efer & EFER_SCE))
 		return emulate_ud(ctxt);
 
+	setup_syscalls_segments(ctxt, &cs, &ss);
 	ops->get_msr(ctxt, MSR_STAR, &msr_data);
 	msr_data >>= 32;
 	cs_sel = (u16)(msr_data & 0xfffc);
@@ -2838,12 +2837,11 @@ static int em_sysenter(struct x86_emulate_ctxt *ctxt)
 	if (ctxt->mode == X86EMUL_MODE_PROT64)
 		return X86EMUL_UNHANDLEABLE;
 
-	setup_syscalls_segments(ctxt, &cs, &ss);
-
 	ops->get_msr(ctxt, MSR_IA32_SYSENTER_CS, &msr_data);
 	if ((msr_data & 0xfffc) == 0x0)
 		return emulate_gp(ctxt, 0);
 
+	setup_syscalls_segments(ctxt, &cs, &ss);
 	ctxt->eflags &= ~(X86_EFLAGS_VM | X86_EFLAGS_IF);
 	cs_sel = (u16)msr_data & ~SEGMENT_RPL_MASK;
 	ss_sel = cs_sel + 8;