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

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