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    Subject[PATCH] Hibernation: Document __save_processor_state() on x86-64
    Date
    From: Rafael J. Wysocki <rjw@sisk.pl>

    Document the fact that __save_processor_state() has to save all CPU
    registers referred to by the kernel in case a different kernel is
    used to load and restore a hibernation image containing it.

    Sigend-off-by: Rafael J. Wysocki <rjw@sisk.pl>
    ---
    arch/x86/kernel/suspend_64.c | 20 ++++++++++++++++++++
    1 file changed, 20 insertions(+)

    Index: linux-2.6/arch/x86/kernel/suspend_64.c
    ===================================================================
    --- linux-2.6.orig/arch/x86/kernel/suspend_64.c
    +++ linux-2.6/arch/x86/kernel/suspend_64.c
    @@ -19,6 +19,21 @@ extern const void __nosave_begin, __nosa

    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)
    {
    /*

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