x86: add generic clearcpuid=... option

Add a generic option to clear any cpuid bit. I added it because it was very easy to add with the new generic cpuid disable bitmap and perhaps it will be useful in the future. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

x86: add generic clearcpuid=... option
Add a generic option to clear any cpuid bit. I added it because it was very easy to add with the new generic cpuid disable bitmap and perhaps it will be useful in the future. Signed-off-by: Andi Kleen <ak@suse.de> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Andi Kleen · Ingo Molnar
1 parent 191679fdfa
Showing 3 changed files with 35 additions and 0 deletions Side-by-side Diff
Documentation/kernel-parameters.txt
arch/x86/kernel/cpu/common.c
arch/x86/kernel/setup_64.c
@@ -416,6 +416,19 @@
 			[SPARC64] tick
 			[X86-64] hpet,tsc
  
+	clearcpuid=BITNUM [X86]
+			Disable CPUID feature X for the kernel. See
+			include/asm-x86/cpufeature.h for the valid bit numbers.
+			Note the Linux specific bits are not necessarily
+			stable over kernel options, but the vendor specific
+			ones should be.
+			Also note that user programs calling CPUID directly
+			or using the feature without checking anything
+			will still see it. This just prevents it from
+			being used by the kernel or shown in /proc/cpuinfo.
+			Also note the kernel might malfunction if you disable
+			some critical bits.
+
 	code_bytes	[IA32/X86_64] How many bytes of object code to print
 			in an oops report.
 			Range: 0 - 8192
@@ -572,6 +572,17 @@
 		printk("\n");
 }
  
+static __init int setup_disablecpuid(char *arg)
+{
+	int bit;
+	if (get_option(&arg, &bit) && bit < NCAPINTS*32)
+		setup_clear_cpu_cap(bit);
+	else
+		return 0;
+	return 1;
+}
+__setup("clearcpuid=", setup_disablecpuid);
+
 cpumask_t cpu_initialized __cpuinitdata = CPU_MASK_NONE;
  
 /* This is hacky. :)
@@ -1050,6 +1050,17 @@
 		printk(KERN_CONT "\n");
 }
  
+static __init int setup_disablecpuid(char *arg)
+{
+	int bit;
+	if (get_option(&arg, &bit) && bit < NCAPINTS*32)
+		setup_clear_cpu_cap(bit);
+	else
+		return 0;
+	return 1;
+}
+__setup("clearcpuid=", setup_disablecpuid);
+
 /*
  *	Get CPU information for use by the procfs.
  */
...	...	@@ -416,6 +416,19 @@
416	416	[SPARC64] tick
417	417	[X86-64] hpet,tsc
418	418
	419	+ clearcpuid=BITNUM [X86]
	420	+ Disable CPUID feature X for the kernel. See
	421	+ include/asm-x86/cpufeature.h for the valid bit numbers.
	422	+ Note the Linux specific bits are not necessarily
	423	+ stable over kernel options, but the vendor specific
	424	+ ones should be.
	425	+ Also note that user programs calling CPUID directly
	426	+ or using the feature without checking anything
	427	+ will still see it. This just prevents it from
	428	+ being used by the kernel or shown in /proc/cpuinfo.
	429	+ Also note the kernel might malfunction if you disable
	430	+ some critical bits.
	431	+
419	432	code_bytes [IA32/X86_64] How many bytes of object code to print
420	433	in an oops report.
421	434	Range: 0 - 8192
...	...	@@ -572,6 +572,17 @@
572	572	printk("\n");
573	573	}
574	574
	575	+static __init int setup_disablecpuid(char *arg)
	576	+{
	577	+ int bit;
	578	+ if (get_option(&arg, &bit) && bit < NCAPINTS*32)
	579	+ setup_clear_cpu_cap(bit);
	580	+ else
	581	+ return 0;
	582	+ return 1;
	583	+}
	584	+__setup("clearcpuid=", setup_disablecpuid);
	585	+
575	586	cpumask_t cpu_initialized __cpuinitdata = CPU_MASK_NONE;
576	587
577	588	/* This is hacky. :)
...	...	@@ -1050,6 +1050,17 @@
1050	1050	printk(KERN_CONT "\n");
1051	1051	}
1052	1052
	1053	+static __init int setup_disablecpuid(char *arg)
	1054	+{
	1055	+ int bit;
	1056	+ if (get_option(&arg, &bit) && bit < NCAPINTS*32)
	1057	+ setup_clear_cpu_cap(bit);
	1058	+ else
	1059	+ return 0;
	1060	+ return 1;
	1061	+}
	1062	+__setup("clearcpuid=", setup_disablecpuid);
	1063	+
1053	1064	/*
1054	1065	* Get CPU information for use by the procfs.
1055	1066	*/