Patch "powerpc/tm: Flush TM only if CPU has TM feature" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/tm: Flush TM only if CPU has TM feature

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-tm-flush-tm-only-if-cpu-has-tm-feature.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Gustavo Romero <[email protected]>
Date: Wed, 13 Sep 2017 22:13:48 -0400
Subject: powerpc/tm: Flush TM only if CPU has TM feature

From: Gustavo Romero <[email protected]>

commit c1fa0768a8713b135848f78fd43ffc208d8ded70 upstream.

Commit cd63f3c ("powerpc/tm: Fix saving of TM SPRs in core dump") added code to access TM SPRs in flush_tmregs_to_thread(). However flush_tmregs_to_thread() does not check if TM feature is available on CPU before trying to access TM SPRs in order to copy live state to thread structures. flush_tmregs_to_thread() is indeed guarded by CONFIG_PPC_TRANSACTIONAL_MEM but it might be the case that kernel was compiled with CONFIG_PPC_TRANSACTIONAL_MEM enabled and ran on a CPU without TM feature available, thus rendering the execution of TM instructions that are treated by the CPU as illegal instructions.

The fix is just to add proper checking in flush_tmregs_to_thread() if CPU has the TM feature before accessing any TM-specific resource, returning immediately if TM is no available on the CPU. Adding that checking in flush_tmregs_to_thread() instead of in places where it is called, like in vsr_get() and vsr_set(), is better because avoids the same problem cropping up elsewhere.

index 07cd22e35405..f52ad5bb7109 100644
@@ -131,7 +131,7 @@ static void flush_tmregs_to_thread(struct task_struct *tsk)
 	 * in the appropriate thread structures from live.
 	 */
 
-	if (tsk != current)
+	if ((!cpu_has_feature(CPU_FTR_TM)) || (tsk != current))
 		return;
 
 	if (MSR_TM_SUSPENDED(mfmsr())) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/powerpc-tm-flush-tm-only-if-cpu-has-tm-feature.patch