linux-kernel - Re: Removing MAX_ARG_PAGES (request for comments/assistance)

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Date:	Wed, 11 Oct 2006 15:14:20 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ollie Wild <aaw@...gle.com>
Cc:	linux-kernel@...r.kernel.org, parisc-linux@...ts.parisc-linux.org,
	Linus Torvalds <torvalds@...l.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, linux-mm@...ck.org,
	Andrew Morton <akpm@...l.org>, Andi Kleen <ak@....de>,
	linux-arch@...r.kernel.org, David Howells <dhowells@...hat.com>
Subject: Re: Removing MAX_ARG_PAGES (request for comments/assistance)

On Tue, 2006-10-10 at 17:05 -0700, Ollie Wild wrote:

> +                       vma->vm_flags &= ~VM_EXEC;
> +               // FIXME: Are the next two lines sufficient, or do I need to
> +               // do some additional magic?
> +               vma->vm_flags |= mm->def_flags;
> +               vma->vm_page_prot = protection_map[vma->vm_flags & 0x7];

Yeah, you'll need to change the PTEs for those pages you created by
calling get_user_page() by calling an mprotect like function; perhaps
something like:

 struct vm_area_struct *prev;
 unsigned long vm_flags = vma->vm_flags;

 s/vma->vm_flags/vm_flags/g

 err = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end, vm_flags);
 BUG_ON(prev != vma);

mprotect_fixup will then set the new protection on all PTEs and update
vma->vm_flags and vma->vm_page_prot.

> +               /* Move stack pages down in memory. */
> +               if (stack_shift) {
> +                       // FIXME: Verify the shift is OK.
> +

What exactly are you wondering about? the call to move_vma looks sane to
me

> +                       /* This should be safe even with overlap because we
> +                        * are shifting down. */
> +                       ret = move_vma(vma, vma->vm_start,
> +                                       vma->vm_end - vma->vm_start,
> +                                       vma->vm_end - vma->vm_start,
> +                                       vma->vm_start - stack_shift);
> +                       if (ret & ~PAGE_MASK) {
> +                               up_write(&mm->mmap_sem);
> +                               return ret;
> +                       }
>                 }


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