Defaults to zero when built as a module and to
10 seconds when built into the kernel.
- clearcpuid=BITNUM[,BITNUM...] [X86]
+ clearcpuid=X[,X...] [X86]
Disable CPUID feature X for the kernel. See
arch/x86/include/asm/cpufeatures.h for the valid bit
- numbers. Note the Linux specific bits are not necessarily
- stable over kernel options, but the vendor specific
+ numbers X. Note the Linux-specific bits are not necessarily
+ stable over kernel options, but the vendor-specific
ones should be.
+ X can also be a string as appearing in the flags: line
+ in /proc/cpuinfo which does not have the above
+ instability issue. However, not all features have names
+ in /proc/cpuinfo.
+ Note that using this option will taint your kernel.
Also note that user programs calling CPUID directly
or using the feature without checking anything
will still see it. This just prevents it from
CPUID_8000_001F_EAX,
};
+#define X86_CAP_FMT_NUM "%d:%d"
+#define x86_cap_flag_num(flag) ((flag) >> 5), ((flag) & 31)
+
#ifdef CONFIG_X86_FEATURE_NAMES
extern const char * const x86_cap_flags[NCAPINTS*32];
extern const char * const x86_power_flags[32];
#define X86_CAP_FMT "%s"
#define x86_cap_flag(flag) x86_cap_flags[flag]
#else
-#define X86_CAP_FMT "%d:%d"
-#define x86_cap_flag(flag) ((flag) >> 5), ((flag) & 31)
+#define X86_CAP_FMT X86_CAP_FMT_NUM
+#define x86_cap_flag x86_cap_flag_num
#endif
/*
static void __init cpu_parse_early_param(void)
{
char arg[128];
- char *argptr = arg;
- int arglen, res, bit;
+ char *argptr = arg, *opt;
+ int arglen, taint = 0;
#ifdef CONFIG_X86_32
if (cmdline_find_option_bool(boot_command_line, "no387"))
return;
pr_info("Clearing CPUID bits:");
- do {
- res = get_option(&argptr, &bit);
- if (res == 0 || res == 3)
- break;
- /* If the argument was too long, the last bit may be cut off */
- if (res == 1 && arglen >= sizeof(arg))
- break;
+ while (argptr) {
+ bool found __maybe_unused = false;
+ unsigned int bit;
+
+ opt = strsep(&argptr, ",");
+
+ /*
+ * Handle naked numbers first for feature flags which don't
+ * have names.
+ */
+ if (!kstrtouint(opt, 10, &bit)) {
+ if (bit < NCAPINTS * 32) {
+
+#ifdef CONFIG_X86_FEATURE_NAMES
+ /* empty-string, i.e., ""-defined feature flags */
+ if (!x86_cap_flags[bit])
+ pr_cont(" " X86_CAP_FMT_NUM, x86_cap_flag_num(bit));
+ else
+#endif
+ pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+
+ setup_clear_cpu_cap(bit);
+ taint++;
+ }
+ /*
+ * The assumption is that there are no feature names with only
+ * numbers in the name thus go to the next argument.
+ */
+ continue;
+ }
+
+#ifdef CONFIG_X86_FEATURE_NAMES
+ for (bit = 0; bit < 32 * NCAPINTS; bit++) {
+ if (!x86_cap_flag(bit))
+ continue;
- if (bit >= 0 && bit < NCAPINTS * 32) {
- pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+ if (strcmp(x86_cap_flag(bit), opt))
+ continue;
+
+ pr_cont(" %s", opt);
setup_clear_cpu_cap(bit);
+ taint++;
+ found = true;
+ break;
}
- } while (res == 2);
+
+ if (!found)
+ pr_cont(" (unknown: %s)", opt);
+#endif
+ }
pr_cont("\n");
+
+ if (taint)
+ add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
}
/*