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Message-Id: <1370772454-6106-5-git-send-email-bp@alien8.de>
Date: Sun, 9 Jun 2013 12:07:33 +0200
From: Borislav Petkov <bp@...en8.de>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
Borislav Petkov <bp@...e.de>
Subject: [PATCH 4/5] x86: Add a static_cpu_has_safe variant
From: Borislav Petkov <bp@...e.de>
We want to use this in early code where alternatives might not have run
yet and for that case we fall back to the dynamic boot_cpu_has.
For that, force a 5-byte jump since the compiler could be generating
differently sized jumps for each label.
Signed-off-by: Borislav Petkov <bp@...e.de>
---
arch/x86/include/asm/cpufeature.h | 86 ++++++++++++++++++++++++++++++++++++++-
arch/x86/kernel/cpu/common.c | 6 +++
2 files changed, 91 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index eba671c0e5b1..0a803b74ac35 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -357,6 +357,7 @@ extern const char * const x86_power_flags[32];
#if __GNUC__ >= 4
extern void warn_pre_alternatives(void);
+extern bool __static_cpu_has_safe(u16 bit);
/*
* Static testing of CPU features. Used the same as boot_cpu_has().
@@ -437,11 +438,94 @@ static __always_inline __pure bool __static_cpu_has(u16 bit)
__static_cpu_has(bit) : \
boot_cpu_has(bit) \
)
+
+static __always_inline __pure bool _static_cpu_has_safe(u16 bit)
+{
+#if __GNUC__ > 4 || __GNUC_MINOR__ >= 5
+/*
+ * We need to spell the jumps to the compiler because, depending on the offset,
+ * the replacement jump can be bigger than the original jump, and this we cannot
+ * have. Thus, we force the jump to the widest, 4-byte, signed relative
+ * offset even though the last would often fit in less bytes.
+ */
+ asm goto("1: .byte 0xe9\n .long %l[t_dynamic] - 2f\n"
+ "2:\n"
+ ".section .altinstructions,\"a\"\n"
+ " .long 1b - .\n" /* src offset */
+ " .long 3f - .\n" /* repl offset */
+ " .word %P1\n" /* always replace */
+ " .byte 2b - 1b\n" /* src len */
+ " .byte 4f - 3f\n" /* repl len */
+ ".previous\n"
+ ".section .altinstr_replacement,\"ax\"\n"
+ "3: .byte 0xe9\n .long %l[t_no] - 2b\n"
+ "4:\n"
+ ".previous\n"
+ ".section .altinstructions,\"a\"\n"
+ " .long 1b - .\n" /* src offset */
+ " .long 0\n" /* no replacement */
+ " .word %P0\n" /* feature bit */
+ " .byte 2b - 1b\n" /* src len */
+ " .byte 0\n" /* repl len */
+ ".previous\n"
+ : : "i" (bit), "i" (X86_FEATURE_ALWAYS)
+ : : t_dynamic, t_no);
+ return true;
+ t_no:
+ return false;
+ t_dynamic:
+ return __static_cpu_has_safe(bit);
+#else /* GCC_VERSION >= 40500 */
+ u8 flag;
+ /* Open-coded due to __stringify() in ALTERNATIVE() */
+ asm volatile("1: movb $2,%0\n"
+ "2:\n"
+ ".section .altinstructions,\"a\"\n"
+ " .long 1b - .\n" /* src offset */
+ " .long 3f - .\n" /* repl offset */
+ " .word %P2\n" /* always replace */
+ " .byte 2b - 1b\n" /* source len */
+ " .byte 4f - 3f\n" /* replacement len */
+ ".previous\n"
+ ".section .discard,\"aw\",@progbits\n"
+ " .byte 0xff + (4f-3f) - (2b-1b)\n" /* size check */
+ ".previous\n"
+ ".section .altinstr_replacement,\"ax\"\n"
+ "3: movb $0,%0\n"
+ "4:\n"
+ ".previous\n"
+ ".section .altinstructions,\"a\"\n"
+ " .long 1b - .\n" /* src offset */
+ " .long 5f - .\n" /* repl offset */
+ " .word %P1\n" /* feature bit */
+ " .byte 4b - 3b\n" /* src len */
+ " .byte 6f - 5f\n" /* repl len */
+ ".previous\n"
+ ".section .discard,\"aw\",@progbits\n"
+ " .byte 0xff + (6f-5f) - (4b-3b)\n" /* size check */
+ ".previous\n"
+ ".section .altinstr_replacement,\"ax\"\n"
+ "5: movb $1,%0\n"
+ "6:\n"
+ ".previous\n"
+ : "=qm" (flag)
+ : "i" (bit), "i" (X86_FEATURE_ALWAYS));
+ return (flag == 2 ? __static_cpu_has_safe(bit) : flag);
+#endif
+}
+
+#define static_cpu_has_safe(bit) \
+( \
+ __builtin_constant_p(boot_cpu_has(bit)) ? \
+ boot_cpu_has(bit) : \
+ _static_cpu_has_safe(bit) \
+)
#else
/*
* gcc 3.x is too stupid to do the static test; fall back to dynamic.
*/
-#define static_cpu_has(bit) boot_cpu_has(bit)
+#define static_cpu_has(bit) boot_cpu_has(bit)
+#define static_cpu_has_safe(bit) boot_cpu_has(bit)
#endif
#define cpu_has_bug(c, bit) cpu_has(c, (bit))
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 407510155f40..f30267ac9371 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1373,3 +1373,9 @@ void warn_pre_alternatives(void)
}
EXPORT_SYMBOL_GPL(warn_pre_alternatives);
#endif
+
+inline bool __static_cpu_has_safe(u16 bit)
+{
+ return boot_cpu_has(bit);
+}
+EXPORT_SYMBOL_GPL(__static_cpu_has_safe);
--
1.8.3
--
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