powerpc: Save the TAR register earlier

This moves us to save the Target Address Register (TAR) a earlier in
__switch_to.  It introduces a new function save_tar() to do this.

We need to save the TAR earlier as we will overwrite it in the transactional
memory reclaim/recheckpoint path.  We are going to do this in a subsequent
patch which will fix saving the TAR register when it's modified inside a
transaction.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Cc: <stable@vger.kernel.org> [v3.10]
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 10 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index c517dbe705fd..8083be20fe5e 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c
@@ -600,6 +600,16 @@ struct task_struct *__switch_to(struct task_struct *prev,
         struct ppc64_tlb_batch *batch;
 #endif
 
+        /* Back up the TAR across context switches.
+         * Note that the TAR is not available for use in the kernel.  (To
+         * provide this, the TAR should be backed up/restored on exception
+         * entry/exit instead, and be in pt_regs.  FIXME, this should be in
+         * pt_regs anyway (for debug).)
+         * Save the TAR here before we do treclaim/trecheckpoint as these
+         * will change the TAR.
+         */
+        save_tar(&prev->thread);
+
         __switch_to_tm(prev);
 
 #ifdef CONFIG_SMP