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SubjectRe: [PATCH v6 2/2] ARM hibernation / suspend-to-disk
On Thu, Feb 27, 2014 at 11:57:58PM +0000, Sebastian Capella wrote:

[...]

> diff --git a/arch/arm/kernel/hibernate.c b/arch/arm/kernel/hibernate.c
> new file mode 100644
> index 0000000..a41e0e3
> --- /dev/null
> +++ b/arch/arm/kernel/hibernate.c
> @@ -0,0 +1,113 @@
> +/*
> + * Hibernation support specific for ARM
> + *
> + * Derived from work on ARM hibernation support by:
> + *
> + * Ubuntu project, hibernation support for mach-dove
> + * Copyright (C) 2010 Nokia Corporation (Hiroshi Doyu)
> + * Copyright (C) 2010 Texas Instruments, Inc. (Teerth Reddy et al.)
> + * https://lkml.org/lkml/2010/6/18/4
> + * https://lists.linux-foundation.org/pipermail/linux-pm/2010-June/027422.html
> + * https://patchwork.kernel.org/patch/96442/
> + *
> + * Copyright (C) 2006 Rafael J. Wysocki <rjw@sisk.pl>
> + *
> + * License terms: GNU General Public License (GPL) version 2
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/suspend.h>
> +#include <asm/tlbflush.h>
> +#include <asm/cacheflush.h>
You can drop tlbflush.h and cacheflush.h, they do not seem to be needed.

> +#include <asm/system_misc.h>
> +#include <asm/idmap.h>
> +#include <asm/suspend.h>
> +
> +extern const void __nosave_begin, __nosave_end;
> +
> +int pfn_is_nosave(unsigned long pfn)
> +{
> + unsigned long nosave_begin_pfn =
> + __pa_symbol(&__nosave_begin) >> PAGE_SHIFT;
> + unsigned long nosave_end_pfn =
> + PAGE_ALIGN(__pa_symbol(&__nosave_end)) >> PAGE_SHIFT;
> +
> + return (pfn >= nosave_begin_pfn) && (pfn < nosave_end_pfn);
> +}
> +
> +void notrace save_processor_state(void)
> +{
> + WARN_ON(num_online_cpus() != 1);
> + local_fiq_disable();
> +}
> +
> +void notrace restore_processor_state(void)
> +{
> + local_fiq_enable();
> +}
> +
> +/*
> + * Snapshot kernel memory and reset the system.
> + *
> + * swsusp_save() is executed in the suspend finisher so that the CPU
> + * context pointer and memory are part of the saved image, which is
> + * required by the resume kernel image to restart execution from
> + * swsusp_arch_suspend().
> + *
> + * soft_restart is not technically needed, but is used to get success
> + * returned from cpu_suspend.
> + *
> + * When soft reboot completes, the hibernation snapshot is written out.
> + */
> +static int notrace arch_save_image(unsigned long unused)
> +{
> + int ret;
> +
> + ret = swsusp_save();
> + if (ret == 0)
> + soft_restart(virt_to_phys(cpu_resume));
> + return ret;
> +}
> +
> +/*
> + * Save the current CPU state before suspend / poweroff.
> + */
> +int notrace swsusp_arch_suspend(void)
> +{
> + return cpu_suspend(0, arch_save_image);
> +}
> +
> +/*
> + * The framework loads the hibernation image into a linked list anchored
> + * at restore_pblist, for swsusp_arch_resume() to copy back to the proper
> + * destinations.
> + *
> + * To make this work if resume is triggered from initramfs, the
> + * pagetables need to be switched to allow writes to kernel mem.
> + */

Comment above needs updating. We are switching page tables to a set of
page tables that are certain to live at the same location in the older
kernel, that's the only reason, as we discussed. soft_restart will make
sure (again) to switch to 1:1 page tables so that we can call cpu_resume
with the MMU off.

> +static void notrace arch_restore_image(void *unused)
> +{
> + struct pbe *pbe;
> +
> + cpu_switch_mm(idmap_pgd, &init_mm);
> + for (pbe = restore_pblist; pbe; pbe = pbe->next)
> + copy_page(pbe->orig_address, pbe->address);
> +
> + soft_restart(virt_to_phys(cpu_resume));
> +}
> +
> +static u8 resume_stack[PAGE_SIZE/2] __nosavedata;
> +
> +/*
> + * Resume from the hibernation image.
> + * Due to the kernel heap / data restore, stack contents change underneath
> + * and that would make function calls impossible; switch to a temporary
> + * stack within the nosave region to avoid that problem.
> + */
> +int swsusp_arch_resume(void)
> +{
> + extern void call_with_stack(void (*fn)(void *), void *arg, void *sp);
> + call_with_stack(arch_restore_image, 0,
> + resume_stack + sizeof(resume_stack));

This does not guarantee your stack is 8-byte aligned, that's not AAPCS
compliant and might buy you trouble.

Either you align the stack or you align the pointer you are passing.

Please have a look at kernel/process.c

Thanks,
Lorenzo



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