Re: [PATCH v3 1/9] mm: Introduce new vm_insert_range API

[Robin Murphy]

On 2018-12-07 7:28 pm, Souptick Joarder wrote:
> On Fri, Dec 7, 2018 at 10:41 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> > On Fri, Dec 07, 2018 at 03:34:56PM +0000, Robin Murphy wrote:
> > > > +int vm_insert_range(struct vm_area_struct *vma, unsigned long addr,
> > > > +                   struct page **pages, unsigned long page_count)
> > > > +{
> > > > +   unsigned long uaddr = addr;
> > > > +   int ret = 0, i;
> > >
> > > Some of the sites being replaced were effectively ensuring that vma and
> > > pages were mutually compatible as an initial condition - would it be worth
> > > adding something here for robustness, e.g.:
> > >
> > > +     if (page_count != vma_pages(vma))
> > > +             return -ENXIO;
> >
> > I think we want to allow this to be used to populate part of a VMA.
> > So perhaps:
> >
> >          if (page_count > vma_pages(vma))
> >                  return -ENXIO;
>
> Ok, This can be added.
>
> I think Patch [2/9] is the only leftover place where this
> check could be removed.

Right, 9/9 could also have relied on my stricter check here, but since 
it's really testing whether it actually managed to allocate vma_pages() 
worth of pages earlier, Matthew's more lenient version won't help for 
that one. (Why privcmd_buf_mmap() doesn't clean up and return an error 
as soon as that allocation loop fails, without taking the mutex under 
which it still does a bunch more pointless work to only undo it again, 
is a mind-boggling mystery, but that's not our problem here...)

Robin.