[PATCH] powerpc/tm: do not use r13 for tabort_syscall

[Nicholas Piggin <npiggin@gmail.com>]

tabort_syscall runs with RI=1, so a nested recoverable machine
check will load the paca into r13 and overwrite what we loaded
it with, because exceptions returning to privileged mode do not
restore r13.

Fixes: b4b56f9ecab4 (powerpc/tm: Abort syscalls in active transactions)
Cc: stable@vger.kernel.org
Signed-off-by: Nick Piggin <npiggin@gmail.com>
---
 arch/powerpc/kernel/entry_64.S | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 73e461a..96fd031 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -368,13 +368,13 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 tabort_syscall:
 	/* Firstly we need to enable TM in the kernel */
 	mfmsr	r10
-	li	r13, 1
-	rldimi	r10, r13, MSR_TM_LG, 63-MSR_TM_LG
+	li	r9, 1
+	rldimi	r10, r9, MSR_TM_LG, 63-MSR_TM_LG
 	mtmsrd	r10, 0
 
 	/* tabort, this dooms the transaction, nothing else */
-	li	r13, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
-	TABORT(R13)
+	li	r9, (TM_CAUSE_SYSCALL|TM_CAUSE_PERSISTENT)
+	TABORT(R9)
 
 	/*
 	 * Return directly to userspace. We have corrupted user register state,
@@ -382,8 +382,8 @@ tabort_syscall:
 	 * resume after the tbegin of the aborted transaction with the
 	 * checkpointed register state.
 	 */
-	li	r13, MSR_RI
-	andc	r10, r10, r13
+	li	r9, MSR_RI
+	andc	r10, r10, r9
 	mtmsrd	r10, 1
 	mtspr	SPRN_SRR0, r11
 	mtspr	SPRN_SRR1, r12
-- 
2.8.1