Re: pipe/page fault oddness.

[Linus Torvalds]

On Thu, Oct 2, 2014 at 7:25 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote:
>
> I don't see what prevents the code to make zero page writable here.
> We need at least pmd = pmd_wrprotect(pmd) before set_pmd_at();

Do we? If it's the zero page, it had better be an anonymous mapping,
and vm_page_prot had better not be writable.

Anonymous pages don't _start_ out writable, we explicitly make them so
with code like

        if (vma->vm_flags & VM_WRITE)
                entry = pte_mkwrite(pte_mkdirty(entry));

so it should be fine to just use "pmd_modify(pmd, vma->vm_page_prot);" directly.

But hey, this is the kind of thing that maybe I'm missing something on..

              Linus
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