x86, mm: fault.c, give another attempt at prefetch handing before SIGBUS

Impact: extend prefetch handling on 64-bit

Currently there's an extra is_prefetch() check done in do_sigbus(),
which we only do on 32 bits.

This is a last-ditch check before we terminate a task, so it's worth
giving prefetch instructions another chance - should none of our
existing quirks have caught a prefetch instruction related spurious
fault.

The only risk is if a prefetch causes a real sigbus, in that case
we'll not OOM but try another fault. But this code has been on
32-bit for a long time, so it should be fine in practice.

So do this on 64-bit too - and thus remove one more #ifdef.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/fault.c

@@ -836,11 +836,9 @@ do_sigbus(struct pt_regs *regs, unsigned long error_code, unsigned long address)
 	if (!(error_code & PF_USER))
 		no_context(regs, error_code, address);
 
-#ifdef CONFIG_X86_32
-	/* User space => ok to do another page fault: */
+	/* User-space => ok to do another page fault: */
 	if (is_prefetch(regs, error_code, address))
 		return;
-#endif
 
 	tsk->thread.cr2		= address;
 	tsk->thread.error_code	= error_code;