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>

diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 49a13e0..294c2ce 100644 (file)
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h
@@ -15,6 +15,15 @@ extern struct task_struct *__switch_to(struct task_struct *,
 struct thread_struct;
 extern struct task_struct *_switch(struct thread_struct *prev,
                                   struct thread_struct *next);
+#ifdef CONFIG_PPC_BOOK3S_64
+static inline void save_tar(struct thread_struct *prev)
+{
+       if (cpu_has_feature(CPU_FTR_ARCH_207S))
+               prev->tar = mfspr(SPRN_TAR);
+}
+#else
+static inline void save_tar(struct thread_struct *prev) {}
+#endif
 
 extern void giveup_fpu(struct task_struct *);
 extern void load_up_fpu(void);

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 4674fe6..2bd0b88 100644 (file)
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -449,15 +449,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_DSCR)
 
 #ifdef CONFIG_PPC_BOOK3S_64
 BEGIN_FTR_SECTION
-       /*
-        * 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).)
-        */
-       mfspr   r0,SPRN_TAR
-       std     r0,THREAD_TAR(r3)
-
        /* Event based branch registers */
        mfspr   r0, SPRN_BESCR
        std     r0, THREAD_BESCR(r3)

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index c517dbe..8083be2 100644 (file)
--- 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