x86/bugs: Add Hygon Dhyana to the respective mitigation machinery

The Hygon Dhyana CPU has the same speculative execution as AMD family
17h, so share AMD spectre mitigation code with Hygon Dhyana.

Also Hygon Dhyana is not affected by meltdown, so add exception for it.

Signed-off-by: Pu Wen <puwen@hygon.cn>
Signed-off-by: Borislav Petkov <bp@suse.de>
Cc: tglx@linutronix.de
Cc: mingo@redhat.com
Cc: hpa@zytor.com
Cc: x86@kernel.org
Cc: thomas.lendacky@amd.com
Link: https://lkml.kernel.org/r/0861d39c8a103fc0deca15bafbc85d403666d9ef.1537533369.git.puwen@hygon.cn

arch/x86/kernel/cpu/bugs.c

@@ -312,6 +312,7 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
 	}
 
 	if (cmd == SPECTRE_V2_CMD_RETPOLINE_AMD &&
+	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON &&
 	    boot_cpu_data.x86_vendor != X86_VENDOR_AMD) {
 		pr_err("retpoline,amd selected but CPU is not AMD. Switching to AUTO select\n");
 		return SPECTRE_V2_CMD_AUTO;
@@ -371,7 +372,8 @@ static void __init spectre_v2_select_mitigation(void)
 	return;
 
 retpoline_auto:
-	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
+	if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+	    boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
 	retpoline_amd:
 		if (!boot_cpu_has(X86_FEATURE_LFENCE_RDTSC)) {
 			pr_err("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n");

arch/x86/kernel/cpu/common.c

@@ -963,6 +963,7 @@ static const __initconst struct x86_cpu_id cpu_no_speculation[] = {
 
 static const __initconst struct x86_cpu_id cpu_no_meltdown[] = {
 	{ X86_VENDOR_AMD },
+	{ X86_VENDOR_HYGON },
 	{}
 };