i386: Allow KVM on i386 nonpae

Currently, CONFIG_X86_CMPXCHG64 both enables boot-time checking of
the cmpxchg64b feature and enables compilation of the set_64bit() family.
Since the option is dependent on PAE, and since KVM depends on set_64bit(),
this effectively disables KVM on i386 nopae.

Simplify by removing the config option altogether: the boot check is made
dependent on CONFIG_X86_PAE directly, and the set_64bit() family is exposed
without constraints. It is up to users to check for the feature flag (KVM
does not as virtualiation extensions imply its existence).

Signed-off-by: Avi Kivity <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/i386/Kconfig.cpu

···
 	depends on !M386
 	default y
 
-config X86_CMPXCHG64
-	bool
-	depends on X86_PAE
-	default y
-
 config X86_ALIGNMENT_16
 	bool
 	depends on MWINCHIP3D || MWINCHIP2 || MWINCHIPC6 || MCYRIXIII || X86_ELAN || MK6 || M586MMX || M586TSC || M586 || M486 || MVIAC3_2 || MGEODEGX1

arch/i386/defconfig

···
 CONFIG_X86_INVLPG=y
 CONFIG_X86_BSWAP=y
 CONFIG_X86_POPAD_OK=y
-CONFIG_X86_CMPXCHG64=y
 CONFIG_X86_GOOD_APIC=y
 CONFIG_X86_INTEL_USERCOPY=y
 CONFIG_X86_USE_PPRO_CHECKSUM=y

arch/um/defconfig

···
 CONFIG_X86_INVLPG=y
 CONFIG_X86_BSWAP=y
 CONFIG_X86_POPAD_OK=y
-CONFIG_X86_CMPXCHG64=y
 CONFIG_X86_GOOD_APIC=y
 CONFIG_X86_USE_PPRO_CHECKSUM=y
 CONFIG_X86_TSC=y

drivers/kvm/Kconfig

···
 config KVM
 	tristate "Kernel-based Virtual Machine (KVM) support"
 	depends on X86 && EXPERIMENTAL
-	depends on X86_CMPXCHG64 || 64BIT
 	---help---
 	  Support hosting fully virtualized guest machines using hardware
 	  virtualization extensions.  You will need a fairly recent

include/asm-i386/cmpxchg.h

···
 
 #include <linux/bitops.h> /* for LOCK_PREFIX */
 
+/*
+ * Note: if you use set64_bit(), __cmpxchg64(), or their variants, you
+ *       you need to test for the feature in boot_cpu_data.
+ */
+
 #define xchg(ptr,v) ((__typeof__(*(ptr)))__xchg((unsigned long)(v),(ptr),sizeof(*(ptr))))
 
 struct __xchg_dummy { unsigned long a[100]; };
 #define __xg(x) ((struct __xchg_dummy *)(x))
-
-
-#ifdef CONFIG_X86_CMPXCHG64
 
 /*
  * The semantics of XCHGCMP8B are a bit strange, this is why
···
 (__builtin_constant_p(value) ? \
  __set_64bit(ptr, (unsigned int)(value), (unsigned int)((value)>>32ULL) ) : \
  __set_64bit(ptr, ll_low(value), ll_high(value)) )
-
-#endif
 
 /*
  * Note: no "lock" prefix even on SMP: xchg always implies lock anyway
···
 })
 #endif
 
-#ifdef CONFIG_X86_CMPXCHG64
-
 static inline unsigned long long __cmpxchg64(volatile void *ptr, unsigned long long old,
 				      unsigned long long new)
 {
···
 #define cmpxchg64_local(ptr,o,n)\
 	((__typeof__(*(ptr)))__cmpxchg64_local((ptr),(unsigned long long)(o),\
 					(unsigned long long)(n)))
-#endif
-
 #endif

include/asm-i386/required-features.h

···
 # define NEED_CMOV	0
 #endif
 
-#ifdef CONFIG_X86_CMPXCHG64
+#ifdef CONFIG_X86_PAE
 # define NEED_CX8	(1<<(X86_FEATURE_CX8 & 31))
 #else
 # define NEED_CX8	0