linux-kernel - [PATCH v4 09/17] x86/clearcpuid: Support feature flag string in kernel option clearcpuid

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Message-Id: <1551494711-213533-10-git-send-email-fenghua.yu@intel.com>
Date:   Fri,  1 Mar 2019 18:45:03 -0800
From:   Fenghua Yu <fenghua.yu@...el.com>
To:     "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...en8.de>,
        "H Peter Anvin" <hpa@...or.com>,
        "Paolo Bonzini" <pbonzini@...hat.com>,
        "Dave Hansen" <dave.hansen@...el.com>,
        "Ashok Raj" <ashok.raj@...el.com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Ravi V Shankar" <ravi.v.shankar@...el.com>,
        "Xiaoyao Li " <xiaoyao.li@...el.com>
Cc:     "linux-kernel" <linux-kernel@...r.kernel.org>,
        "x86" <x86@...nel.org>, kvm@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: [PATCH v4 09/17] x86/clearcpuid: Support feature flag string in kernel option clearcpuid

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@...el.com>
---
 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 ce95b8cbd229..6792088525e3 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -132,6 +132,7 @@ 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 5ba11ce99f92..b84b133d0ebd 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);
 	}
-- 
2.7.4