From: sebastian.capella@linaro•org (Sebastian Capella)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v6 2/2] ARM hibernation / suspend-to-disk
Date: Fri, 28 Feb 2014 15:38:54 -0800 [thread overview]
Message-ID: <53111e0f.a50a430a.6ef6.ffff99ae@mx.google.com> (raw)
In-Reply-To: <20140228224933.GA11040@e102568-lin.cambridge.arm.com>
Quoting Lorenzo Pieralisi (2014-02-28 14:49:33)
> On Fri, Feb 28, 2014 at 08:15:57PM +0000, Sebastian Capella wrote:
>
> [...]
>
> > > > +
> > > > +/*
> > > > + * 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.
> >
> > How does this look?
> >
> > The framework loads as much of the hibernation image to final physical
> > pages as possible. Any pages that were in use, will need to be restored
> > prior to the soft_restart. The pages to restore are maintained in
> > the list anchored at restore_pblist. At this point, we can swap the
> > pages to their final location. We must switch the mapping to 1:1 to
> > ensure that when we overwrite the page table physical pages we're using
> > a known physical location (idmap_pgd) with known contents.
>
> It is ok, a tad too verbose. All I care about is a comment describing
> what's really needed, the existing one was confusing and wrong.
Maybe more like:
Restore physical pages that were in use while loading hibernation image.
Use idmap_pgd so our page tables use the same physical address as the
hibernation image. Will be overwriten with the same contents.
> > > > +/*
> > > > + * 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
> >
> > I've added this for now, do you see any issues?
> >
> > -static u8 resume_stack[PAGE_SIZE/2] __nosavedata;
> > +static u64 resume_stack[PAGE_SIZE/2/sizeof(u64)] __nosavedata;
> > - resume_stack + sizeof(resume_stack));
> > + resume_stack + ARRAY_SIZE(resume_stack));
>
> I do not see why the stack depends on the PAGE_SIZE. I would be surprised
> if you need more than a few bytes (given that soft_restart switches stack
> again...), go through it with a debugger, it is easy to check the stack
> usage and allow for some extra buffer (but half a page is not needed).
I assuming this is becase the no-save region is one page anyway (we skip
restoring the no-save region physical page). So maybe 1/2 is a way to
leave some room for whatever else may need to be here, but in any case
the 4k is used for nosave. I think you're right that it can be much less.
I'll check into this...
Thanks!
Sebastian
next prev parent reply other threads:[~2014-02-28 23:38 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-27 23:57 [PATCH v6 0/2] hibernation support on ARM Sebastian Capella
2014-02-27 23:57 ` [PATCH v6 1/2] ARM: avoid tracers in soft_restart Sebastian Capella
2014-02-27 23:57 ` [PATCH v6 2/2] ARM hibernation / suspend-to-disk Sebastian Capella
2014-02-28 0:09 ` Stephen Boyd
2014-02-28 1:47 ` Russ Dill
2014-02-28 2:19 ` Stephen Boyd
2014-02-28 10:20 ` Russell King - ARM Linux
[not found] ` <20140228181731.29118.41809@capellas-linux>
2014-03-05 2:28 ` Sebastian Capella
2014-06-02 16:57 ` Sebastian Capella
2014-02-28 9:50 ` Lorenzo Pieralisi
2014-02-28 20:15 ` Sebastian Capella
2014-02-28 22:49 ` Lorenzo Pieralisi
2014-02-28 23:38 ` Sebastian Capella [this message]
2014-03-04 9:55 ` Sebastian Capella
2014-03-04 11:17 ` Lorenzo Pieralisi
2014-03-05 0:18 ` Sebastian Capella
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