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

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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.
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