From 927df12f19c9b557875fe5a7dec4759f97af1b6c Mon Sep 17 00:00:00 2001
From: James Morse <james.morse@arm.com>
Date: Tue, 18 Oct 2016 11:27:48 +0100
Subject: [PATCH] arm64: suspend: Reconfigure PSTATE after resume from idle

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@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
 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(-)

diff --git a/arch/arm64/include/asm/exec.h b/arch/arm64/include/asm/exec.h
index db0563c23482d..f7865dd9d8685 100644
--- a/arch/arm64/include/asm/exec.h
+++ b/arch/arm64/include/asm/exec.h
@@ -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 */
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 27b2f1387df40..4f186c56c5ebf 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -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>
@@ -301,7 +302,7 @@ static void tls_thread_switch(struct task_struct *next)
 }
 
 /* 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)
diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
index ad734142070dc..bb0cd787a9d31 100644
--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -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>
@@ -49,6 +52,14 @@ void notrace __cpu_suspend_exit(void)
 	 */
 	set_my_cpu_offset(per_cpu_offset(cpu));
 
+	/*
+	 * 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
-- 
2.39.5