From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
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(-)
--
2.25.1
