powerpc/ptrace: Fix coredump since ptrace TM changes

Commit 8d460f6156 ("powerpc/process: Add the function
flush_tmregs_to_thread") added flush_tmregs_to_thread() and included
the assumption that it would only be called for a task which is not
current.

Although this is correct for ptrace, when generating a core dump, some
of the routines which call flush_tmregs_to_thread() are called. This
leads to a WARNing such as:

  Not expecting ptrace on self: TM regs may be incorrect
  ------------[ cut here ]------------
  WARNING: CPU: 123 PID: 7727 at arch/powerpc/kernel/process.c:1088 flush_tmregs_to_thread+0x78/0x80
  CPU: 123 PID: 7727 Comm: libvirtd Not tainted 4.8.0-rc1-gcc6x-g61e8a0d #1
  task: c000000fe631b600 task.stack: c000000fe63b0000
  NIP: c00000000001a1a8 LR: c00000000001a1a4 CTR: c000000000717780
  REGS: c000000fe63b3420 TRAP: 0700   Not tainted  (4.8.0-rc1-gcc6x-g61e8a0d)
  MSR: 900000010282b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]>  CR: 28004222  XER: 20000000
  ...
  NIP [c00000000001a1a8] flush_tmregs_to_thread+0x78/0x80
  LR [c00000000001a1a4] flush_tmregs_to_thread+0x74/0x80
  Call Trace:
   flush_tmregs_to_thread+0x74/0x80 (unreliable)
   vsr_get+0x64/0x1a0
   elf_core_dump+0x604/0x1430
   do_coredump+0x5fc/0x1200
   get_signal+0x398/0x740
   do_signal+0x54/0x2b0
   do_notify_resume+0x98/0xb0
   ret_from_except_lite+0x70/0x74

So fix flush_tmregs_to_thread() to detect the case where it is called on
current, and a transaction is active, and in that case flush the TM regs
to the thread_struct.

This patch also moves flush_tmregs_to_thread() into ptrace.c as it is
only called from that file.

Fixes: 8d460f6156 ("powerpc/process: Add the function flush_tmregs_to_thread")
Signed-off-by: Cyril Bur <cyrilbur@gmail.com>
[mpe: Flesh out change log]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/switch_to.h

@@ -75,14 +75,6 @@ static inline void disable_kernel_spe(void)
 static inline void __giveup_spe(struct task_struct *t) { }
 #endif
 
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-extern void flush_tmregs_to_thread(struct task_struct *);
-#else
-static inline void flush_tmregs_to_thread(struct task_struct *t)
-{
-}
-#endif
-
 static inline void clear_task_ebb(struct task_struct *t)
 {
 #ifdef CONFIG_PPC_BOOK3S_64

arch/powerpc/kernel/process.c

@@ -1074,26 +1074,6 @@ static inline void restore_sprs(struct thread_struct *old_thread,
 #endif
 }
 
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-void flush_tmregs_to_thread(struct task_struct *tsk)
-{
-	/*
-	 * Process self tracing is not yet supported through
-	 * ptrace interface. Ptrace generic code should have
-	 * prevented this from happening in the first place.
-	 * Warn once here with the message, if some how it
-	 * is attempted.
-	 */
-	WARN_ONCE(tsk == current,
-		"Not expecting ptrace on self: TM regs may be incorrect\n");
-
-	/*
-	 * If task is not current, it should have been flushed
-	 * already to it's thread_struct during __switch_to().
-	 */
-}
-#endif
-
 struct task_struct *__switch_to(struct task_struct *prev,
 	struct task_struct *new)
 {

arch/powerpc/kernel/ptrace.c

@@ -38,6 +38,7 @@
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/switch_to.h>
+#include <asm/tm.h>
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/syscalls.h>
@@ -118,6 +119,24 @@ static const struct pt_regs_offset regoffset_table[] = {
 	REG_OFFSET_END,
 };
 
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+static void flush_tmregs_to_thread(struct task_struct *tsk)
+{
+	/*
+	 * If task is not current, it will have been flushed already to
+	 * it's thread_struct during __switch_to().
+	 *
+	 * A reclaim flushes ALL the state.
+	 */
+
+	if (tsk == current && MSR_TM_SUSPENDED(mfmsr()))
+		tm_reclaim_current(TM_CAUSE_SIGNAL);
+
+}
+#else
+static inline void flush_tmregs_to_thread(struct task_struct *tsk) { }
+#endif
+
 /**
  * regs_query_register_offset() - query register offset from its name
  * @name:	the name of a register