x86/retpoline: Remove minimal retpoline support

Now that CONFIG_RETPOLINE hard depends on compiler support, there is no
reason to keep the minimal retpoline support around which only provided
basic protection in the assembly files.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Borislav Petkov <bp@suse.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: <srinivas.eeda@oracle.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/f06f0a89-5587-45db-8ed2-0a9d6638d5c0@default

arch/x86/include/asm/nospec-branch.h

@@ -221,8 +221,6 @@
 /* The Spectre V2 mitigation variants */
 enum spectre_v2_mitigation {
 	SPECTRE_V2_NONE,
-	SPECTRE_V2_RETPOLINE_MINIMAL,
-	SPECTRE_V2_RETPOLINE_MINIMAL_AMD,
 	SPECTRE_V2_RETPOLINE_GENERIC,
 	SPECTRE_V2_RETPOLINE_AMD,
 	SPECTRE_V2_IBRS_ENHANCED,

arch/x86/kernel/cpu/bugs.c

@@ -135,8 +135,6 @@ enum spectre_v2_mitigation_cmd {
 
 static const char *spectre_v2_strings[] = {
 	[SPECTRE_V2_NONE]			= "Vulnerable",
-	[SPECTRE_V2_RETPOLINE_MINIMAL]		= "Vulnerable: Minimal generic ASM retpoline",
-	[SPECTRE_V2_RETPOLINE_MINIMAL_AMD]	= "Vulnerable: Minimal AMD ASM retpoline",
 	[SPECTRE_V2_RETPOLINE_GENERIC]		= "Mitigation: Full generic retpoline",
 	[SPECTRE_V2_RETPOLINE_AMD]		= "Mitigation: Full AMD retpoline",
 	[SPECTRE_V2_IBRS_ENHANCED]		= "Mitigation: Enhanced IBRS",
@@ -250,11 +248,6 @@ static void __init spec2_print_if_secure(const char *reason)
 		pr_info("%s selected on command line.\n", reason);
 }
 
-static inline bool retp_compiler(void)
-{
-	return __is_defined(CONFIG_RETPOLINE);
-}
-
 static inline bool match_option(const char *arg, int arglen, const char *opt)
 {
 	int len = strlen(opt);
@@ -417,14 +410,12 @@ retpoline_auto:
 			pr_err("Spectre mitigation: LFENCE not serializing, switching to generic retpoline\n");
 			goto retpoline_generic;
 		}
-		mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_AMD :
+		mode = SPECTRE_V2_RETPOLINE_AMD;
-					 SPECTRE_V2_RETPOLINE_MINIMAL_AMD;
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE_AMD);
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 	} else {
 	retpoline_generic:
-		mode = retp_compiler() ? SPECTRE_V2_RETPOLINE_GENERIC :
+		mode = SPECTRE_V2_RETPOLINE_GENERIC;
-					 SPECTRE_V2_RETPOLINE_MINIMAL;
 		setup_force_cpu_cap(X86_FEATURE_RETPOLINE);
 	}