linux-kernel - Re: [RFC][PATCH -mm] Make swsusp work on i386 with PAE

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Date:	Mon, 23 Oct 2006 17:29:10 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Pavel Machek <pavel@....cz>
Cc:	Linux PM <linux-pm@...l.org>, Dave Jones <davej@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Nigel Cunningham <ncunningham@...uxmail.org>
Subject: Re: [RFC][PATCH -mm] Make swsusp work on i386 with PAE

Hi,

On Monday, 23 October 2006 16:50, Pavel Machek wrote:
> Hi!
> 
> > The purpose of the appended patch is to make swsusp work on i386 with PAE,
> > but it should also allow i386 systems without PSE to use swsusp.
> > 
> > The patch creates temporary page tables located in resume-safe page frames
> > during the resume and uses them for restoring the suspend image (the same
> > approach is used on x86-64).
> > 
> > It has been tested on an i386 system with PAE and survived several
> > suspend-resume cycles in a row, but I have no systems without PSE, so that
> > requires some testing.
> 
> Thanks, looks okay to me. I guess Andi Kleen would be right person to
> review it in detail?

Yes, I think so.

> Lack of assembly modifications is good.
> 
> I guess this should be now removed? (include/asm-i386/suspend.h)
> 
> arch_prepare_suspend(void)
> {
>         /* If you want to make non-PSE machine work, turn off paging
>            in swsusp_arch_suspend. swsusp_pg_dir should have identity mapping, so
>            it could work...  */
>         if (!cpu_has_pse) {
>                 printk(KERN_ERR "PSE is required for swsusp.\n");
>                 return -EPERM;
>         }

Yes, it should.  I though it went away when the Kconfig was changed ...

> > +/*
> > + * Create a middle page table on a resume-safe page and put a pointer to it in
> > + * the given global directory entry.  This only returns the gd entry
> > + * in non-PAE compilation mode, since the middle layer is folded.
> > + */
> > +static pmd_t *resume_one_md_table_init(pgd_t *pgd)
> > +{
> > +	pud_t *pud;
> > +	pmd_t *pmd_table;
> > +
> > +#ifdef CONFIG_X86_PAE
> > +	pmd_table = (pmd_t *)get_safe_page(GFP_ATOMIC);
> > +	if (!pmd_table)
> > +		return pmd_table;
> 
> I'd do plain old return NULL; here.

OK

> > +			/* Map with big pages if possible, otherwise create
> > +			 * normal page tables.
> > +			 * NOTE: We can mark everything as executable here
> > +			 */
> > +			if (cpu_has_pse) {
> > +				set_pmd(pmd, pfn_pmd(pfn, PAGE_KERNEL_LARGE_EXEC));
> > +				pfn += PTRS_PER_PTE;
> 
> Perhaps disabling PSE here can help getting some testing?

Well, I don't really want to make everyone test the !PSE scenario. ;-)

> Okay, I guess I should really test this one... Seems good enough for
> -mm to me, but it should preferably stay there for a _long_ time.

I think so too.

Greetings,
Rafael


-- 
You never change things by fighting the existing reality.
		R. Buckminster Fuller
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