lkml.org 
[lkml]   [2020]   [Sep]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[RFC PATCH] Use feature bit names in clearcpuid=
Hi,

so tglx hates this clearcpuid= interface where you have to give the
X86_FEATURE array indices in order to disable a feature bit for testing.
Below is a first attempt (lightly tested in a VM only) to accept the bit
names from /proc/cpuinfo too.

I say "too" because not all feature bits have names and we would still
have to support the numbers. Yeah, yuck.

An exemplary cmdline would then be something like:

clearcpuid=de,440,smca,succory,bmi1,3dnow ("succory" is wrong on
purpose).

and it says:

[ 0.000000] Clearing CPUID bits: de 13:24 smca bmi1 3dnow

Also, I'm thinking we should taint the kernel when this option is used.

Thoughts?

---
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 59bf91c57aa8..10b65045fc37 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -32,14 +32,17 @@ enum cpuid_leafs
CPUID_7_EDX,
};

+#define X86_CAP_FMT_BARE "%d:%d"
+#define x86_cap_flag_bare(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_BARE
+#define x86_cap_flag(flag) x86_cap_flag_bare((flag))
#endif

/*
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index f8ff895aaf7e..17be3c99b65d 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -244,8 +244,8 @@ static void __init fpu__init_system_ctx_switch(void)
static void __init fpu__init_parse_early_param(void)
{
char arg[128];
- char *argptr = arg;
- int arglen, res, bit;
+ char *argptr = arg, *opt;
+ int arglen, bit, taint = 0;

#ifdef CONFIG_X86_32
if (cmdline_find_option_bool(boot_command_line, "no387"))
@@ -273,21 +273,45 @@ static void __init fpu__init_parse_early_param(void)
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;
-
- if (bit >= 0 && bit < NCAPINTS * 32) {
- pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
- setup_clear_cpu_cap(bit);
+
+ while (argptr) {
+ int i;
+
+ opt = (strsep(&argptr, ","));
+ if (!opt)
+ continue;
+
+ if (!kstrtoint(opt, 10, &bit)) {
+ if (bit >= 0 && bit < NCAPINTS * 32) {
+ if (!x86_cap_flag(bit))
+ pr_cont(" " X86_CAP_FMT_BARE, x86_cap_flag_bare(bit));
+ else
+ pr_cont(" " X86_CAP_FMT, x86_cap_flag(bit));
+
+ setup_clear_cpu_cap(bit);
+ taint++;
+ continue;
+ }
}
- } while (res == 2);
+
+#ifdef CONFIG_X86_FEATURE_NAMES
+ for (i = 0; i < 32 * NCAPINTS; i++) {
+ if (!x86_cap_flags[i])
+ continue;
+
+ if (strcmp(x86_cap_flags[i], opt))
+ continue;
+
+ pr_cont(" %s", opt);
+ setup_clear_cpu_cap(i);
+ taint++;
+ }
+#endif
+ }
pr_cont("\n");
+
+ if (taint)
+ add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK);
}

/*
--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

\
 
 \ /
  Last update: 2020-09-20 17:42    [W:0.078 / U:0.696 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site