x86/cpu: Add X86_FEATURE_CPUID

Add a synthetic CPUID flag denoting whether the CPU sports the CPUID
instruction or not. This will come useful later when accomodating
CPUID-less CPUs.

Signed-off-by: Borislav Petkov <bp@suse.de>
[ Slightly prettified. ]
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Whitehead <tedheadster@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>
Link: http://lkml.kernel.org/r/dcb355adae3ab812c79397056a61c212f1a0c7cc.1484705016.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/cpufeatures.h

@@ -100,7 +100,7 @@
 #define X86_FEATURE_XTOPOLOGY	( 3*32+22) /* cpu topology enum extensions */
 #define X86_FEATURE_TSC_RELIABLE ( 3*32+23) /* TSC is known to be reliable */
 #define X86_FEATURE_NONSTOP_TSC	( 3*32+24) /* TSC does not stop in C states */
-/* free, was #define X86_FEATURE_CLFLUSH_MONITOR ( 3*32+25) * "" clflush reqd with monitor */
+#define X86_FEATURE_CPUID	( 3*32+25) /* CPU has CPUID instruction itself */
 #define X86_FEATURE_EXTD_APICID	( 3*32+26) /* has extended APICID (8 bits) */
 #define X86_FEATURE_AMD_DCM     ( 3*32+27) /* multi-node processor */
 #define X86_FEATURE_APERFMPERF	( 3*32+28) /* APERFMPERF */

arch/x86/kernel/cpu/common.c

@@ -801,14 +801,12 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 	memset(&c->x86_capability, 0, sizeof c->x86_capability);
 	c->extended_cpuid_level = 0;
 
-	if (!have_cpuid_p())
-		identify_cpu_without_cpuid(c);
-
 	/* cyrix could have cpuid enabled via c_identify()*/
 	if (have_cpuid_p()) {
 		cpu_detect(c);
 		get_cpu_vendor(c);
 		get_cpu_cap(c);
+		setup_force_cpu_cap(X86_FEATURE_CPUID);
 
 		if (this_cpu->c_early_init)
 			this_cpu->c_early_init(c);
@@ -818,6 +816,9 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
 
 		if (this_cpu->c_bsp_init)
 			this_cpu->c_bsp_init(c);
+	} else {
+		identify_cpu_without_cpuid(c);
+		setup_clear_cpu_cap(X86_FEATURE_CPUID);
 	}
 
 	setup_force_cpu_cap(X86_FEATURE_ALWAYS);