[RFC PATCH 08/14] powerpc/tm: Recheckpoint at exit path

[Breno Leitao <leitao@debian.org>]

In the past, TIF_RESTORE_TM was being handled with the rest of the TIF workers,
but, that was too early, and can cause some IRQ to be replayed in suspended
state (after recheckpoint).

This patch moves TIF_RESTORE_TM handler to as late as possible, it also
forces the IRQ to be disabled, and it will continue to be until RFID, so,
no IRQ will be replayed at all. I.e, if trecheckpoint happens, it will RFID
to userspace.

This makes TIF_RESTORE_TM a special case that should not be handled
similarly to the _TIF_USER_WORK_MASK.

Since _TIF_RESTORE_TM is not part of _TIF_USER_WORK_MASK anymore, we
need to force system_call_exit to continue to leaves through
fast_exception_return, so, we add the flags together with
_TIF_USER_WORK_MASK at system_call_exist path.

If this flag is set at system_call_exit, it means that recheckpoint
will be called, and doing it through fast_exception_return is the only
way to do so.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 arch/powerpc/include/asm/thread_info.h |  2 +-
 arch/powerpc/kernel/entry_64.S         | 23 ++++++++++++++---------
 2 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index 544cac0474cb..2835d60bc9ef 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -139,7 +139,7 @@ void arch_setup_new_exec(void);
 
 #define _TIF_USER_WORK_MASK	(_TIF_SIGPENDING | _TIF_NEED_RESCHED | \
 				 _TIF_NOTIFY_RESUME | _TIF_UPROBE | \
-				 _TIF_RESTORE_TM | _TIF_PATCH_PENDING | \
+				 _TIF_PATCH_PENDING | \
 				 _TIF_FSCHECK)
 #define _TIF_PERSYSCALL_MASK	(_TIF_RESTOREALL|_TIF_NOERROR)
 
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 17484ebda66c..a86619edf29d 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -255,7 +255,7 @@ system_call_exit:
 
 	ld	r9,TI_FLAGS(r12)
 	li	r11,-MAX_ERRNO
-	andi.	r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK)
+	andi.   r0,r9,(_TIF_SYSCALL_DOTRACE|_TIF_SINGLESTEP|_TIF_USER_WORK_MASK|_TIF_PERSYSCALL_MASK |_TIF_RESTORE_TM)
 	bne-	.Lsyscall_exit_work
 
 	andi.	r0,r8,MSR_FP
@@ -784,14 +784,6 @@ _GLOBAL(ret_from_except_lite)
 	SCHEDULE_USER
 	b	ret_from_except_lite
 2:
-#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
-	andi.	r0,r4,_TIF_USER_WORK_MASK & ~_TIF_RESTORE_TM
-	bne	3f		/* only restore TM if nothing else to do */
-	addi	r3,r1,STACK_FRAME_OVERHEAD
-	bl	restore_tm_state
-	b	restore
-3:
-#endif
 	bl	save_nvgprs
 	/*
 	 * Use a non volatile GPR to save and restore our thread_info flags
@@ -938,6 +930,19 @@ ALT_FTR_SECTION_END_IFCLR(CPU_FTR_STCX_CHECKS_ADDRESS)
 	 */
 	.globl	fast_exception_return
 fast_exception_return:
+
+#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
+	CURRENT_THREAD_INFO(r4, r1)
+	ld	r4,TI_FLAGS(r4)
+	andi.   r0,r4,_TIF_RESTORE_TM
+	beq	22f
+	ld	r4,_MSR(r1) 	/* TODO: MSR[!PR] shouldn't be here */
+	andi.	r0,r4,MSR_PR
+	beq	22f  /* Skip if Kernel thread */
+	addi	r3,r1,STACK_FRAME_OVERHEAD
+	bl	restore_tm_state
+22:
+#endif
 	ld	r3,_MSR(r1)
 	ld	r4,_CTR(r1)
 	ld	r0,_LINK(r1)
-- 
2.19.0