Re: [PATCH 05/13] mm/frame-vector: Use FOLL_LONGTERM

Daniel Vetter
2020-10-07T17:12:38Z

On Wed, Oct 7, 2020 at 6:53 PM Jason Gunthorpe <jgg@ziepe.ca> wrote:
>
> On Wed, Oct 07, 2020 at 06:44:18PM +0200, Daniel Vetter wrote:
> >
> > - /*
> > - * While get_vaddr_frames() could be used for transient (kernel
> > - * controlled lifetime) pinning of memory pages all current
> > - * users establish long term (userspace controlled lifetime)
> > - * page pinning. Treat get_vaddr_frames() like
> > - * get_user_pages_longterm() and disallow it for filesystem-dax
> > - * mappings.
> > - */
> > - if (vma_is_fsdax(vma)) {
> > - ret = -EOPNOTSUPP;
> > - goto out;
> > - }
> > -
> > - if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
> > - vec->got_ref = true;
> > - vec->is_pfns = false;
> > - ret = pin_user_pages_locked(start, nr_frames,
> > - gup_flags, (struct page **)(vec->ptrs), &locked);
> > - goto out;
> > - }
>
> The vm_flags still need to be checked before going into the while
> loop. If the break is taken then nothing would check vm_flags

Hm right that's a bin inconsistent. follow_pfn also checks for this,
so I think we can just ditch this entirely both here and in the do {}
while () check, simplifying the latter to just while (vma). Well, just
make it a real loop with less confusing control flow probably.

Or prefer I keep this and touch the code less?
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation