linux-kernel - [PATCH] x86/boot: Do not test if AC and ID eflags are changeable on x86

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Message-ID: <20250307091022.181136-1-ubizjak@gmail.com>
Date: Fri,  7 Mar 2025 10:10:03 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: x86@...nel.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH] x86/boot: Do not test if AC and ID eflags are changeable on x86_64

The test for the changeabitily of AC and ID eflags is used to
distinguish between i386 and i486 processors (AC) and to test
for cpuid instruction support (ID).

Skip these tests on x86_64 processors as they always supports cpuid.

Also change the return type of has_eflag() to bool.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: "H. Peter Anvin" <hpa@...or.com>
---
 arch/x86/boot/cpuflags.c | 26 +++++++++-----------------
 arch/x86/boot/cpuflags.h |  6 +++++-
 2 files changed, 14 insertions(+), 18 deletions(-)

diff --git a/arch/x86/boot/cpuflags.c b/arch/x86/boot/cpuflags.c
index d75237ba7ce9..2150a016176f 100644
--- a/arch/x86/boot/cpuflags.c
+++ b/arch/x86/boot/cpuflags.c
@@ -29,40 +29,32 @@ static int has_fpu(void)
 	return fsw == 0 && (fcw & 0x103f) == 0x003f;
 }
 
+#ifdef CONFIG_X86_32
 /*
  * For building the 16-bit code we want to explicitly specify 32-bit
  * push/pop operations, rather than just saying 'pushf' or 'popf' and
- * letting the compiler choose. But this is also included from the
- * compressed/ directory where it may be 64-bit code, and thus needs
- * to be 'pushfq' or 'popfq' in that case.
+ * letting the compiler choose.
  */
-#ifdef __x86_64__
-#define PUSHF "pushfq"
-#define POPF "popfq"
-#else
-#define PUSHF "pushfl"
-#define POPF "popfl"
-#endif
-
-int has_eflag(unsigned long mask)
+bool has_eflag(unsigned long mask)
 {
 	unsigned long f0, f1;
 
-	asm volatile(PUSHF "	\n\t"
-		     PUSHF "	\n\t"
+	asm volatile("pushfl	\n\t"
+		     "pushfl	\n\t"
 		     "pop %0	\n\t"
 		     "mov %0,%1	\n\t"
 		     "xor %2,%1	\n\t"
 		     "push %1	\n\t"
-		     POPF "	\n\t"
-		     PUSHF "	\n\t"
+		     "popfl	\n\t"
+		     "pushfl	\n\t"
 		     "pop %1	\n\t"
-		     POPF
+		     "popfl"
 		     : "=&r" (f0), "=&r" (f1)
 		     : "ri" (mask));
 
 	return !!((f0^f1) & mask);
 }
+#endif
 
 void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d)
 {
diff --git a/arch/x86/boot/cpuflags.h b/arch/x86/boot/cpuflags.h
index fdcc2aa4c3c4..a398d9204ad0 100644
--- a/arch/x86/boot/cpuflags.h
+++ b/arch/x86/boot/cpuflags.h
@@ -15,7 +15,11 @@ struct cpu_features {
 extern struct cpu_features cpu;
 extern u32 cpu_vendor[3];
 
-int has_eflag(unsigned long mask);
+#ifdef CONFIG_X86_32
+bool has_eflag(unsigned long mask);
+#else
+static inline bool has_eflag(unsigned long mask) { return true; }
+#endif
 void get_cpuflags(void);
 void cpuid_count(u32 id, u32 count, u32 *a, u32 *b, u32 *c, u32 *d);
 bool has_cpuflag(int flag);
-- 
2.48.1