Patch "arm64: suspend: Reconfigure PSTATE after resume from idle" has been added to the 4.4-stable tree

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

arm64: suspend: Reconfigure PSTATE after resume from idle

to the 4.4-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:
arm64-suspend-reconfigure-pstate-after-resume-from-idle.patch
and it can be found in the queue-4.4 subdirectory.

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

From: James Morse <[email protected]>
Date: Tue, 18 Oct 2016 11:27:48 +0100
Subject: arm64: suspend: Reconfigure PSTATE after resume from idle

From: James Morse <[email protected]>

commit d08544127d9fb4505635e3cb6871fd50a42947bd upstream.

The suspend/resume path in kernel/sleep.S, as used by cpu-idle, does not save/restore PSTATE. As a result of this cpufeatures that were detected and have bits in PSTATE get lost when we resume from idle.

UAO gets set appropriately on the next context switch. PAN will be re-enabled next time we return from user-space, but on a preemptible kernel we may run work accessing user space before this point.

Add code to re-enable theses two features in __cpu_suspend_exit(). We re-use uao_thread_switch() passing current.

[Removed UAO hooks and commit-message references: this feature is not
present in v4.4]

---
 arch/arm64/kernel/suspend.c |    9 +++++++++
 1 file changed, 9 insertions(+)

@@ -1,7 +1,9 @@
 #include <linux/ftrace.h>
 #include <linux/percpu.h>
 #include <linux/slab.h>
+#include <asm/alternative.h>
 #include <asm/cacheflush.h>
+#include <asm/cpufeature.h>
 #include <asm/debug-monitors.h>
 #include <asm/pgtable.h>
 #include <asm/memory.h>

@@ -111,6 +113,13 @@ int cpu_suspend(unsigned long arg, int (
 		set_my_cpu_offset(per_cpu_offset(smp_processor_id()));
 
 		/*
+		 * PSTATE was not saved over suspend/resume, re-enable any
+		 * detected features that might not have been set correctly.
+		 */
+		asm(ALTERNATIVE("nop", SET_PSTATE_PAN(1), ARM64_HAS_PAN,
+				CONFIG_ARM64_PAN));
+
+		/*
 		 * Restore HW breakpoint registers to sane values
 		 * before debug exceptions are possibly reenabled
 		 * through local_dbg_restore.

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

queue-4.4/arm64-mm-set-pstate.pan-from-the-cpu_enable_pan-call.patch queue-4.4/arm64-suspend-reconfigure-pstate-after-resume-from-idle.patch queue-4.4/arm64-cpufeature-schedule-enable-calls-instead-of-calling-them-via-ipi.patch