Previously, we noticed the one rpma example was failed[1] since 36f30e486d, where it will use ODP feature to do RDMA WRITE between fsdax files.

After digging into the code, we found hmm_vma_handle_pte() will still return EFAULT even though all the its requesting flags has been fulfilled. That's because a DAX page will be marked as (_PAGE_SPECIAL | PAGE_DEVMAP) by pte_mkdevmap().

[1]: https://github.com/pmem/rpma/issues/1142

CC: stable@vger.kernel.org Signed-off-by: Li Zhijian lizhijian@cn.fujitsu.com --- mm/hmm.c | 7 +++++++ 1 file changed, 7 insertions(+)

diff --git a/mm/hmm.c b/mm/hmm.c index fad6be2bf072..4766bdefb6c3 100644 --- a/mm/hmm.c +++ b/mm/hmm.c @@ -294,6 +294,12 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, if (required_fault) goto fault;

+ /* + * just bypass devmap pte such as DAX page when all pfn requested + * flags(pfn_req_flags) are fulfilled. + */ + if (pte_devmap(pte)) + goto out; /* * Since each architecture defines a struct page for the zero page, just * fall through and treat it like a normal page. @@ -307,6 +313,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, return 0; }

+out: *hmm_pfn = pte_pfn(pte) | cpu_flags; return 0;