powerpc/tm: do not use r13 for tabort_syscall

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>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 6b8bc0d..5afd03e 100644 (file)
--- 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