linux-kernel - Re: [RFC][PATCH -mm 4/4] Hibernation: Use temporary page tables for kernel text mapping on x86

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Message-ID: <20070824083101.GC2175@elf.ucw.cz>
Date:	Fri, 24 Aug 2007 10:31:01 +0200
From:	Pavel Machek <pavel@....cz>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andi Kleen <ak@...e.de>, LKML <linux-kernel@...r.kernel.org>,
	pm list <linux-pm@...ts.linux-foundation.org>
Subject: Re: [RFC][PATCH -mm 4/4] Hibernation: Use temporary page tables for kernel text mapping on x86_64

On Wed 2007-08-22 18:16:05, Rafael J. Wysocki wrote:
> On Wednesday, 22 August 2007 10:29, Pavel Machek wrote:
> > Hi!
> > 
> > > Use temporary page tables for the kernel text mapping during hibernation restore
> > > on x86_64.
> > > 
> > > Without the patch, the original boot kernel's page tables that represent the
> > > kernel text mapping are used while the core of the image kernel is being
> > > restored.  However, in principle, if the boot kernel is not identical to the
> > > image kernel, the location of these page tables in the image kernel need not be
> > > the same, so we should create a safe copy of the kernel text mapping prior to
> > > restoring the core of the image kernel.
> > 
> > 
> > > @@ -190,25 +190,42 @@ static int res_phys_pud_init(pud_t *pud,
> > >  	return 0;
> > >  }
> > >  
> > > +static int res_kernel_text_pud_init(pud_t *pud, unsigned long start)
> > > +{
> > > +	pmd_t *pmd;
> > > +	unsigned long paddr;
> > > +
> > > +	pmd = (pmd_t *)get_safe_page(GFP_ATOMIC);
> > > +	if (!pmd)
> > > +		return -ENOMEM;
> > > +	set_pud(pud + pud_index(start), __pud(__pa(pmd) | _KERNPG_TABLE));
> > > +	for (paddr = 0; paddr < KERNEL_TEXT_SIZE; pmd++, paddr += PMD_SIZE) {
> > > +		unsigned long pe;
> > > +
> > > +		pe = __PAGE_KERNEL_LARGE_EXEC | _PAGE_GLOBAL | paddr;
> > > +		pe &= __supported_pte_mask;
> > > +		set_pmd(pmd, __pmd(pe));
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static int set_up_temporary_mappings(void)
> > >  {
> > >  	unsigned long start, end, next;
> > > +	pud_t *pud;
> > >  	int error;
> > >  
> > >  	temp_level4_pgt = (pgd_t *)get_safe_page(GFP_ATOMIC);
> > >  	if (!temp_level4_pgt)
> > >  		return -ENOMEM;
> > >  
> > > -	/* It is safe to reuse the original kernel mapping */
> > > -	set_pgd(temp_level4_pgt + pgd_index(__START_KERNEL_map),
> > > -		init_level4_pgt[pgd_index(__START_KERNEL_map)]);
> > > -
> > >  	/* Set up the direct mapping from scratch */
> > >  	start = (unsigned long)pfn_to_kaddr(0);
> > >  	end = (unsigned long)pfn_to_kaddr(end_pfn);
> > >  
> > >  	for (; start < end; start = next) {
> > > -		pud_t *pud = (pud_t *)get_safe_page(GFP_ATOMIC);
> > > +		pud = (pud_t *)get_safe_page(GFP_ATOMIC);
> > >  		if (!pud)
> > >  			return -ENOMEM;
> > 
> > I believe we leak temp_level4_pgt here.
> > 
> > > +	/* Set up the kernel text mapping from scratch */
> > > +	pud = (pud_t *)get_safe_page(GFP_ATOMIC);
> > > +	if (!pud)
> > > +		return -ENOMEM;
> > 
> > ...and some more memory here :-(. 
> 
> No, these pages will be freed by swsusp_free(), thanks to the get_safe_page().
> 
> I'm not _that_ careless. ;-)

Ok, ACK.


-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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