Patch "arm64: suspend: Reconfigure PSTATE after resume from idle" has been added to the 4.8-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 4.8-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-4.8 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.

---
 arch/arm64/include/asm/exec.h |    3 +++
 arch/arm64/kernel/process.c   |    3 ++-
 arch/arm64/kernel/suspend.c   |   11 +++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

@@ -18,6 +18,9 @@
 #ifndef __ASM_EXEC_H
 #define __ASM_EXEC_H
 
+#include <linux/sched.h>
+
 extern unsigned long arch_align_stack(unsigned long sp);
+void uao_thread_switch(struct task_struct *next);
 
 #endif	/* __ASM_EXEC_H */

@@ -49,6 +49,7 @@
 #include <asm/alternative.h>
 #include <asm/compat.h>
 #include <asm/cacheflush.h>
+#include <asm/exec.h>
 #include <asm/fpsimd.h>
 #include <asm/mmu_context.h>
 #include <asm/processor.h>

@@ -303,7 +304,7 @@ static void tls_thread_switch(struct tas
 }
 
 /* Restore the UAO state depending on next's addr_limit */
-static void uao_thread_switch(struct task_struct *next)
+void uao_thread_switch(struct task_struct *next)
 {
 	if (IS_ENABLED(CONFIG_ARM64_UAO)) {
 		if (task_thread_info(next)->addr_limit == KERNEL_DS)

@@ -1,8 +1,11 @@
 #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/exec.h>
 #include <asm/pgtable.h>
 #include <asm/memory.h>
 #include <asm/mmu_context.h>

@@ -48,6 +51,14 @@ void notrace __cpu_suspend_exit(void)
 	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));
+	uao_thread_switch(current);
+
+	/*
 	 * 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-4.8/arm64-mm-set-pstate.pan-from-the-cpu_enable_pan-call.patch queue-4.8/arm64-suspend-reconfigure-pstate-after-resume-from-idle.patch queue-4.8/arm64-cpufeature-schedule-enable-calls-instead-of-calling-them-via-ipi.patch