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authorAndy Lutomirski <luto@kernel.org>2016-09-29 12:48:12 -0700
committerThomas Gleixner <tglx@linutronix.de>2016-09-30 12:40:12 +0200
commit1ef55be16ed69538f89e0a6508be5e62fdc9851c (patch)
tree623f3cb97a13b616e813aeadb46a56689d555141 /arch/x86/include/asm/special_insns.h
parentd7e25c66c9bf882450060fd9464e784bd229d3ae (diff)
x86/asm: Get rid of __read_cr4_safe()
We use __read_cr4() vs __read_cr4_safe() inconsistently. On CR4-less CPUs, all CR4 bits are effectively clear, so we can make the code simpler and more robust by making __read_cr4() always fix up faults on 32-bit kernels. This may fix some bugs on old 486-like CPUs, but I don't have any easy way to test that. Signed-off-by: Andy Lutomirski <luto@kernel.org> Cc: Brian Gerst <brgerst@gmail.com> Cc: Borislav Petkov <bp@alien8.de> Cc: david@saggiorato.net Link: http://lkml.kernel.org/r/ea647033d357d9ce2ad2bbde5a631045f5052fb6.1475178370.git.luto@kernel.org Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'arch/x86/include/asm/special_insns.h')
-rw-r--r--arch/x86/include/asm/special_insns.h22
1 files changed, 7 insertions, 15 deletions
diff --git a/arch/x86/include/asm/special_insns.h b/arch/x86/include/asm/special_insns.h
index 587d7914ea4b..19a2224f9e16 100644
--- a/arch/x86/include/asm/special_insns.h
+++ b/arch/x86/include/asm/special_insns.h
@@ -59,22 +59,19 @@ static inline void native_write_cr3(unsigned long val)
static inline unsigned long native_read_cr4(void)
{
unsigned long val;
- asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" (__force_order));
- return val;
-}
-
-static inline unsigned long native_read_cr4_safe(void)
-{
- unsigned long val;
- /* This could fault if %cr4 does not exist. In x86_64, a cr4 always
- * exists, so it will never fail. */
#ifdef CONFIG_X86_32
+ /*
+ * This could fault if CR4 does not exist. Non-existent CR4
+ * is functionally equivalent to CR4 == 0. Keep it simple and pretend
+ * that CR4 == 0 on CPUs that don't have CR4.
+ */
asm volatile("1: mov %%cr4, %0\n"
"2:\n"
_ASM_EXTABLE(1b, 2b)
: "=r" (val), "=m" (__force_order) : "0" (0));
#else
- val = native_read_cr4();
+ /* CR4 always exists on x86_64. */
+ asm volatile("mov %%cr4,%0\n\t" : "=r" (val), "=m" (__force_order));
#endif
return val;
}
@@ -182,11 +179,6 @@ static inline unsigned long __read_cr4(void)
return native_read_cr4();
}
-static inline unsigned long __read_cr4_safe(void)
-{
- return native_read_cr4_safe();
-}
-
static inline void __write_cr4(unsigned long x)
{
native_write_cr4(x);