[PATCH for-next 2/2] xen/x86: Drop sync_core()

[Andrew Cooper <andrew.cooper3@citrix.com>]

As identified in Linux c/s c198b121b1a1d "x86/asm: Rewrite sync_core() to use
IRET-to-self", sync_core() is only appropriate for two very specific usecases.

Xen doesn't have need of either of these usecases, so drop sync_core() to
avoid any misuse.

In the unlikely event that we do gain a legitimate use for sync_core(), it
should be reintroduced as a mov to %cr2 rather than cpuid, which has a lower
overhead.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
---
 xen/include/asm-x86/processor.h | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index 1d1a4ff..6a335d3 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -396,17 +396,6 @@ static inline bool_t read_pkru_wd(uint32_t pkru, unsigned int pkey)
     outb((data), 0x23); \
 } while (0)
 
-/* Stop speculative execution */
-static inline void sync_core(void)
-{
-    int tmp;
-    asm volatile (
-        "cpuid"
-        : "=a" (tmp)
-        : "0" (1)
-        : "ebx","ecx","edx","memory" );
-}
-
 static always_inline void __monitor(const void *eax, unsigned long ecx,
                                     unsigned long edx)
 {
-- 
2.1.4


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