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

[Souptick Joarder <jrdr.linux@xxxxxxxxx>]

On Sat, Dec 8, 2018 at 2:40 AM Robin Murphy <robin.murphy@xxxxxxx> wrote:
>
> 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...)

I think some clean up can be done here in a separate patch.

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