[PATCH v6 17/20] x86/clearcpuid: Support feature flag string in kernel option clearcpuid

[Fenghua Yu]

The kernel option clearcpuid currently only takes feature bit which
can be changed from kernel to kernel.

Extend clearcpuid to use cap flag string, which is defined in
x86_cap_flags[] and won't be changed from kernel to kernel.
And user can easily get the cap flag string from /proc/cpuinfo.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
---
 arch/x86/include/asm/cpufeature.h |  1 +
 arch/x86/kernel/cpu/cpuid-deps.c  | 26 ++++++++++++++++++++++++++
 arch/x86/kernel/fpu/init.c        |  3 ++-
 3 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 0e56ff7e4848..823c4ab82e12 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -133,6 +133,7 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
 
 extern void setup_clear_cpu_cap(unsigned int bit);
 extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
+bool find_cpu_cap(char *cap_flag, unsigned int *pfeature);
 
 #define setup_force_cpu_cap(bit) do { \
 	set_cpu_cap(&boot_cpu_data, bit);	\
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index 3d633f67fbd7..1a71434f7b46 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -120,3 +120,29 @@ void setup_clear_cpu_cap(unsigned int feature)
 {
 	do_clear_cpu_cap(NULL, feature);
 }
+
+/**
+ * find_cpu_cap - Given a cap flag string, find its corresponding feature bit.
+ * @cap_flag:	cap flag string as defined in x86_cap_flags[]
+ * @pfeature:	feature bit
+ *
+ * Return: true if the feature is found. false if not found
+ */
+bool find_cpu_cap(char *cap_flag, unsigned int *pfeature)
+{
+#ifdef CONFIG_X86_FEATURE_NAMES
+	unsigned int feature;
+
+	for (feature = 0; feature < NCAPINTS * 32; feature++) {
+		if (!x86_cap_flags[feature])
+			continue;
+
+		if (strcmp(cap_flag, x86_cap_flags[feature]) == 0) {
+			*pfeature = feature;
+
+			return true;
+		}
+	}
+#endif
+	return false;
+}
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 88bbba7ee96a..99b895eea166 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -256,7 +256,8 @@ static void __init clear_cpuid(void)
 		/* Chang command line range for next search. */
 		cmdline_size = option_pos - boot_command_line + 1;
 		argptr = arg;
-		if (get_option(&argptr, &bit) &&
+		/* cpu cap can be specified by either feature bit or string */
+		if ((get_option(&argptr, &bit) || find_cpu_cap(arg, &bit)) &&
 		    bit >= 0 && bit < NCAPINTS * 32)
 			setup_clear_cpu_cap(bit);
 	}
-- 
2.19.1