Re: [PATCH] Hibernation: Document __save_processor_state() on x86-64

[Pavel Machek <pavel@ucw.cz>]

Hi!

> 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.
> + */

Maybe this warning should be appended to struct saved_context
definition? Reordering its fields (etc) would be bad news, too, and
documentation near data structures is easier to find...

Thanks,
								Pavel

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