On 07/03/2015 05:07 PM, Kirill A. Shutemov wrote: > Reading page fault handler code I've noticed that under right > circumstances kernel would map anonymous pages into file mappings: > if the VMA doesn't have vm_ops->fault() and the VMA wasn't fully > populated on ->mmap(), kernel would handle page fault to not populated > pte with do_anonymous_page(). > > There's chance that it was done intentionally, but I don't see good > justification for this. We just hide bugs in broken drivers. > Have you done a preliminary audit for these broken drivers? If they actually exist in-tree then this patch is a regression for them. We need to look for vm_ops without an .fault = . Perhaps define a map_annonimous() for those to revert to the old behavior, if any actually exist. > Let's change page fault handler to use do_anonymous_page() only on > anonymous VMA (->vm_ops == NULL). > > For file mappings without vm_ops->fault() page fault on pte_none() entry > would lead to SIGBUS. > Again that could mean a theoretical regression for some in-tree driver, do you know of any such driver? Thanks Boaz > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > --- > mm/memory.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/mm/memory.c b/mm/memory.c > index 8a2fc9945b46..f3ee782059e3 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3115,6 +3115,9 @@ static int do_fault(struct mm_struct *mm, struct vm_area_struct *vma, > - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff; > > pte_unmap(page_table); > + > + if (unlikely(!vma->vm_ops->fault)) > + return VM_FAULT_SIGBUS; > if (!(flags & FAULT_FLAG_WRITE)) > return do_read_fault(mm, vma, address, pmd, pgoff, flags, > orig_pte); > @@ -3260,13 +3263,13 @@ static int handle_pte_fault(struct mm_struct *mm, > barrier(); > if (!pte_present(entry)) { > if (pte_none(entry)) { > - if (vma->vm_ops) { > - if (likely(vma->vm_ops->fault)) > - return do_fault(mm, vma, address, pte, > - pmd, flags, entry); > + if (!vma->vm_ops) { > + return do_anonymous_page(mm, vma, address, pte, > + pmd, flags); > + } else { > + return do_fault(mm, vma, address, pte, pmd, > + flags, entry); > } > - return do_anonymous_page(mm, vma, address, > - pte, pmd, flags); > } > return do_swap_page(mm, vma, address, > pte, pmd, flags, entry); > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>