[PATCH 4.4 13/13] arm64: suspend: Reconfigure PSTATE after resume from idle

[Greg Kroah-Hartman]

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

------------------

From: James Morse <james.morse@xxxxxxx>

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.

Signed-off-by: James Morse <james.morse@xxxxxxx>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
[Removed UAO hooks and commit-message references: this feature is not
 present in v4.4]
Signed-off-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -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.