[PATCH hmm 0/8] Various error case bug fixes for hmm_range_fault()

[Jason Gunthorpe]

From: Jason Gunthorpe <jgg at mellanox.com>

The hmm_range_fault() flow is fairly complicated. The scheme allows the
caller to specify if it needs a usable result for each page, or if it only
needs the current page table status filled in. This mixture of behavior is
useful for a caller that wants to build a 'prefetch around fault'
algorithm.

Although we have no in-tree users of this capability, I am working on
having RDMA ODP work in this manner, and removing these bugs from
hmm_range_fault() is a necessary step.

The basic principles are:

 - If the caller did not ask for a VA to be valid then hmm_range_fault()
   should not fail because of that VA

 - If 0 is returned from hmm_range_fault() then the entire pfns array
   contains valid data

 - HMM_PFN_ERROR is set if faulting fails, or if asking for faulting
   would fail

 - A 0 return from hmm_range_fault() does not have HMM_PFN_ERROR in any
   VA's the caller asked to be valid

This series does not get there completely, I have a followup series
closing some more complex cases.

I tested this series using Ralph's hmm tester he posted a while back,
other testing would be appreciated.

Jason Gunthorpe (8):
  mm/hmm: add missing unmaps of the ptep during hmm_vma_handle_pte()
  mm/hmm: don't free the cached pgmap while scanning
  mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock
  mm/hmm: add missing pfns set to hmm_vma_walk_pmd()
  mm/hmm: add missing call to hmm_range_need_fault() before returning
    EFAULT
  mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte()
  mm/hmm: return -EFAULT when setting HMM_PFN_ERROR on requested valid
    pages
  mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL
    handling

 mm/hmm.c | 166 ++++++++++++++++++++++++++-----------------------------
 1 file changed, 79 insertions(+), 87 deletions(-)

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2.25.1