KVM: MIPS: Add CPUCFG emulation for Loongson-3

Loongson-3 overrides lwc2 instructions to implement CPUCFG and CSR
read/write functions. These instructions all cause guest exit so CSR
doesn't benifit KVM guest (and there are always legacy methods to
provide the same functions as CSR). So, we only emulate CPUCFG and let
it return a reduced feature list (which means the virtual CPU doesn't
have any other advanced features, including CSR) in KVM.

Reviewed-by: Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>
Signed-off-by: Huacai Chen <chenhc@lemote.com>
Co-developed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Message-Id: <1590220602-3547-12-git-send-email-chenhc@lemote.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/arch/mips/include/asm/kvm_host.h b/arch/mips/include/asm/kvm_host.h
index c4e6b1e..9f3bfc8 100644
--- a/arch/mips/include/asm/kvm_host.h
+++ b/arch/mips/include/asm/kvm_host.h
@@ -173,6 +173,9 @@ struct kvm_vcpu_stat {
 	u64 vz_ghfc_exits;
 	u64 vz_gpa_exits;
 	u64 vz_resvd_exits;
+#ifdef CONFIG_CPU_LOONGSON64
+	u64 vz_cpucfg_exits;
+#endif
 #endif
 	u64 halt_successful_poll;
 	u64 halt_attempted_poll;