Re: [PATCH 1/5] Add pagetable allocation notifiers

[Zachary Amsden]

Chris Wright wrote:

> * Zachary Amsden (zach@xxxxxxxxxx) wrote:
>  
>
> > --- linux-2.6.13.orig/arch/i386/mm/init.c	2005-08-24 09:31:05.000000000 -0700
> > +++ linux-2.6.13/arch/i386/mm/init.c	2005-08-24 09:31:31.000000000 -0700
> > @@ -79,6 +79,7 @@ static pte_t * __init one_page_table_ini
> > {
> > 	if (pmd_none(*pmd)) {
> > 		pte_t *page_table = (pte_t *) alloc_bootmem_low_pages(PAGE_SIZE);
> > +		SetPagePTE(virt_to_page(page_table));
> >    
>
> Xen has this on one_md_table_init() as well for pmd.
>  

I'll add that in another patch.  It's easy to miss some of the init time 
call sites (we don't actually depend on them for correctness).


> > 	spin_lock_irqsave(&pgd_lock, flags);
> > 	pgd_list_del(pgd);
> > 	spin_unlock_irqrestore(&pgd_lock, flags);
> > @@ -244,13 +246,16 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
> > 		pmd_t *pmd = kmem_cache_alloc(pmd_cache, GFP_KERNEL);
> > 		if (!pmd)
> > 			goto out_oom;
> > +		SetPagePDE(virt_to_page(pmd));
> > 		set_pgd(&pgd[i], __pgd(1 + __pa(pmd)));
> > 	}
> > 	return pgd;
> >
> > out_oom:
> > -	for (i--; i >= 0; i--)
> > +	for (i--; i >= 0; i--) {
> > +		ClearPagePDE(pfn_to_page(pgd_val(pgd[i]) >> PAGE_SHIFT));
> >    
>
> Is that the right pfn?  That -1 throws me off.
>
>  
>
> > 		kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
> > +	}
> > 	kmem_cache_free(pgd_cache, pgd);
> > 	return NULL;
> > }
> > @@ -261,8 +266,10 @@ void pgd_free(pgd_t *pgd)
> >
> > 	/* in the PAE case user pgd entries are overwritten before usage */
> > 	if (PTRS_PER_PMD > 1)
> > -		for (i = 0; i < USER_PTRS_PER_PGD; ++i)
> > -			kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i])-1));
> > +		for (i = 0; i < USER_PTRS_PER_PGD; ++i) {
> > +			ClearPagePDE(pfn_to_page(pgd_val(pgd[i]) >> PAGE_SHIFT));
> > +			kmem_cache_free(pmd_cache, (void *)__va(pgd_val(pgd[i]) & PAGE_MASK));
> >    
>
> Why the switch of kmem_cache_free call?
>  

Because pgd_val(pgd[i])-1 is confusing.   Using (pgd_val(pgd[i]) - 
_PAGE_PRESENT) would be better, but the +/- 1s all over the place here 
could use some general cleanup as well.  I smell a cleanup fit coming 
on.  Using (pgd_val(pgd[i]) & PAGE_MASK) is a less error prone way to 
get the physical frame bits, since it is not wrong if you turn on PCD or 
PWD.

Zach
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