2 files changed, 28 insertions, 1 deletions

diff --git a/arch/x86/kernel/suspend_64.c b/arch/x86/kernel/suspend_64.c
index 2e5efaaf8800..569f1b540e36 100644
--- a/arch/x86/kernel/suspend_64.c
+++ b/arch/x86/kernel/suspend_64.c
@@ -19,6 +19,21 @@ extern const void __nosave_begin, __nosave_end;
 
 struct saved_context saved_context;
 
+/**
+ *      __save_processor_state - save CPU registers before creating a
+ *              hibernation image and before restoring the memory state from it
+ *      @ctxt - structure to store the registers contents in
+ *
+ *      NOTE: If there is a CPU register the modification of which by the
+ *      boot kernel (ie. the kernel used for loading the hibernation image)
+ *      might affect the operations of the restored target kernel (ie. the one
+ *      saved in the hibernation image), then its contents must be saved by this
+ *      function.  In other words, if kernel A is hibernated and different
+ *      kernel B is used for loading the hibernation image into memory, the
+ *      kernel A's __save_processor_state() function must save all registers
+ *      needed by kernel A, so that it can operate correctly after the resume
+ *      regardless of what kernel B does in the meantime.
+ */
 void __save_processor_state(struct saved_context *ctxt)
 {
         kernel_fpu_begin();
@@ -69,6 +84,11 @@ static void do_fpu_end(void)
         kernel_fpu_end();
 }
 
+/**
+ *      __restore_processor_state - restore the contents of CPU registers saved
+ *              by __save_processor_state()
+ *      @ctxt - structure to load the registers contents from
+ */
 void __restore_processor_state(struct saved_context *ctxt)
 {
         /*
diff --git a/include/asm-x86/suspend_64.h b/include/asm-x86/suspend_64.h
index c505a76bcf6e..4404668f9aa4 100644
--- a/include/asm-x86/suspend_64.h
+++ b/include/asm-x86/suspend_64.h
@@ -15,7 +15,14 @@ arch_prepare_suspend(void)
         return 0;
 }
 
-/* Image of the saved processor state. If you touch this, fix acpi/wakeup.S. */
+/*
+ * Image of the saved processor state, used by the low level ACPI suspend to
+ * RAM code and by the low level hibernation code.
+ *
+ * If you modify it, fix arch/x86/kernel/acpi/wakeup_64.S and make sure that
+ * __save/__restore_processor_state(), defined in arch/x86/kernel/suspend_64.c,
+ * still work as required.
+ */
 struct saved_context {
         struct pt_regs regs;
         u16 ds, es, fs, gs, ss;