powerpc/math-emu: Allow math-emu to be used for HW FPU

(Including 64-bit ones)

This allow SW emulation by the kernel of optional instructions
such as fsqrt which aren't implemented on some processors, and
thus fixes some Fedora 19 issues such as Anaconda since the
compiler is set to generate those by default on 64-bit.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/traps.c

@@ -1125,7 +1125,17 @@ void __kprobes program_check_exception(struct pt_regs *regs)
 	 * ESR_DST (!?) or 0.  In the process of chasing this with the
 	 * hardware people - not sure if it can happen on any illegal
 	 * instruction or only on FP instructions, whether there is a
-	 * pattern to occurrences etc. -dgibson 31/Mar/2003 */
+	 * pattern to occurrences etc. -dgibson 31/Mar/2003
+	 */
+
+	/*
+	 * If we support a HW FPU, we need to ensure the FP state
+	 * if flushed into the thread_struct before attempting
+	 * emulation
+	 */
+#ifdef CONFIG_PPC_FPU
+	flush_fp_to_thread(current);
+#endif
 	switch (do_mathemu(regs)) {
 	case 0:
 		emulate_single_step(regs);