linux-kernel - [PATCH v5 1/1] x86/cpu: Make sure flag_is_changeable

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Message-ID: <20241108153105.1578186-1-andriy.shevchenko@linux.intel.com>
Date: Fri,  8 Nov 2024 17:30:10 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Thomas Gleixner <tglx@...utronix.de>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Cc: Ingo Molnar <mingo@...hat.com>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Bill Wendling <morbo@...gle.com>,
	Justin Stitt <justinstitt@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>
Subject: [PATCH v5 1/1] x86/cpu: Make sure flag_is_changeable_p() is always being used

When flag_is_changeable_p() is unused, it prevents kernel builds
with clang, `make W=1` and CONFIG_WERROR=y:

arch/x86/kernel/cpu/common.c:351:19: error: unused function 'flag_is_changeable_p' [-Werror,-Wunused-function]
  351 | static inline int flag_is_changeable_p(u32 flag)
      |                   ^~~~~~~~~~~~~~~~~~~~

Fix this by moving core around to make sure flag_is_changeable_p() is
always being used.

See also commit 6863f5643dd7 ("kbuild: allow Clang to find unused static
inline functions for W=1 build").

While at it, fix the argument type to be unsigned long along with
the local variables, although it currently only runs in 32-bit cases.
Besides that, makes it return boolean instead of int. This induces
the change of the returning type of have_cpuid_p() to be boolean
as well.

Suggested-by: Dave Hansen <dave.hansen@...el.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
---

v5: fixed type of the local vars (hpa), made it return bool (hpa)
v4: fixed the type of parameter (hpa)
v3: rewritten as suggested (Dave)
v2: marked both 32- and 64-bit cases

 arch/x86/include/asm/cpuid.h |  8 +++++---
 arch/x86/kernel/cpu/common.c | 39 +++++++++++++++++-------------------
 2 files changed, 23 insertions(+), 24 deletions(-)

diff --git a/arch/x86/include/asm/cpuid.h b/arch/x86/include/asm/cpuid.h
index ca4243318aad..239b9ba5c398 100644
--- a/arch/x86/include/asm/cpuid.h
+++ b/arch/x86/include/asm/cpuid.h
@@ -6,6 +6,8 @@
 #ifndef _ASM_X86_CPUID_H
 #define _ASM_X86_CPUID_H
 
+#include <linux/types.h>
+
 #include <asm/string.h>
 
 struct cpuid_regs {
@@ -20,11 +22,11 @@ enum cpuid_regs_idx {
 };
 
 #ifdef CONFIG_X86_32
-extern int have_cpuid_p(void);
+bool have_cpuid_p(void);
 #else
-static inline int have_cpuid_p(void)
+static inline bool have_cpuid_p(void)
 {
-	return 1;
+	return true;
 }
 #endif
 static inline void native_cpuid(unsigned int *eax, unsigned int *ebx,
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a5f221ea5688..f361336416ae 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -276,21 +276,13 @@ static int __init x86_noinvpcid_setup(char *s)
 }
 early_param("noinvpcid", x86_noinvpcid_setup);
 
-#ifdef CONFIG_X86_32
-static int cachesize_override = -1;
-static int disable_x86_serial_nr = 1;
-
-static int __init cachesize_setup(char *str)
-{
-	get_option(&str, &cachesize_override);
-	return 1;
-}
-__setup("cachesize=", cachesize_setup);
-
 /* Standard macro to see if a specific flag is changeable */
-static inline int flag_is_changeable_p(u32 flag)
+static inline bool flag_is_changeable_p(unsigned long flag)
 {
-	u32 f1, f2;
+	unsigned long f1, f2;
+
+	if (!IS_ENABLED(CONFIG_X86_32))
+		return true;
 
 	/*
 	 * Cyrix and IDT cpus allow disabling of CPUID
@@ -313,11 +305,22 @@ static inline int flag_is_changeable_p(u32 flag)
 		      : "=&r" (f1), "=&r" (f2)
 		      : "ir" (flag));
 
-	return ((f1^f2) & flag) != 0;
+	return (f1 ^ f2) & flag;
 }
 
+#ifdef CONFIG_X86_32
+static int cachesize_override = -1;
+static int disable_x86_serial_nr = 1;
+
+static int __init cachesize_setup(char *str)
+{
+	get_option(&str, &cachesize_override);
+	return 1;
+}
+__setup("cachesize=", cachesize_setup);
+
 /* Probe for the CPUID instruction */
-int have_cpuid_p(void)
+bool have_cpuid_p(void)
 {
 	return flag_is_changeable_p(X86_EFLAGS_ID);
 }
@@ -349,10 +352,6 @@ static int __init x86_serial_nr_setup(char *s)
 }
 __setup("serialnumber", x86_serial_nr_setup);
 #else
-static inline int flag_is_changeable_p(u32 flag)
-{
-	return 1;
-}
 static inline void squash_the_stupid_serial_number(struct cpuinfo_x86 *c)
 {
 }
@@ -1088,7 +1087,6 @@ void get_cpu_address_sizes(struct cpuinfo_x86 *c)
 
 static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
 {
-#ifdef CONFIG_X86_32
 	int i;
 
 	/*
@@ -1109,7 +1107,6 @@ static void identify_cpu_without_cpuid(struct cpuinfo_x86 *c)
 				break;
 			}
 		}
-#endif
 }
 
 #define NO_SPECULATION		BIT(0)
-- 
2.43.0.rc1.1336.g36b5255a03ac