powerpc: Add isync to copy_and_flush

In __after_prom_start we copy the kernel down to zero in two calls to
copy_and_flush.  After the first call (copy from 0 to copy_to_here:)
we jump to the newly copied code soon after.

Unfortunately there's no isync between the copy of this code and the
jump to it.  Hence it's possible that stale instructions could still be
in the icache or pipeline before we branch to it.

We've seen this on real machines and it's results in no console output
after:
  calling quiesce...
  returning from prom_init

The below adds an isync to ensure that the copy and flushing has
completed before any branching to the new instructions occurs.

Signed-off-by: Michael Neuling <mikey@neuling.org>
CC: <stable@vger.kernel.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 1 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 0886ae6dd5be..b61363d557b5 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -509,6 +509,7 @@ _GLOBAL(copy_and_flush)
         sync
         addi    r5,r5,8
         addi    r6,r6,8
+        isync
         blr
 
 .align 8