4.7-stable review patch.  If anyone has any objections, please let me know.


From: Nicholas Piggin <npig...@gmail.com>

commit cc7786d3ee7e3c979799db834b528db2c0834c2e upstream.

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)
Signed-off-by: Nick Piggin <npig...@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

 arch/powerpc/kernel/entry_64.S |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- 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)
        /* 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 */
-       TABORT(R13)
+       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

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