From: Li Zhijian lizhijian@cn.fujitsu.com Subject: mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled

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

Link: https://lkml.kernel.org/r/20210830094232.203029-1-lizhijian@cn.fujitsu.com Fixes: 405506274922 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling") Signed-off-by: Li Zhijian lizhijian@cn.fujitsu.com Reviewed-by: Christoph Hellwig hch@lst.de Reviewed-by: Jason Gunthorpe jgg@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hmm.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/mm/hmm.c~mm-hmm-bypass-devmap-pte-when-all-pfn-requested-flags-are-fulfilled +++ a/mm/hmm.c @@ -295,10 +295,13 @@ static int hmm_vma_handle_pte(struct mm_ goto fault;

/* + * Bypass devmap pte such as DAX page when all pfn requested + * flags(pfn_req_flags) are fulfilled. * Since each architecture defines a struct page for the zero page, just * fall through and treat it like a normal page. */ - if (pte_special(pte) && !is_zero_pfn(pte_pfn(pte))) { + if (pte_special(pte) && !pte_devmap(pte) && + !is_zero_pfn(pte_pfn(pte))) { if (hmm_pte_need_fault(hmm_vma_walk, pfn_req_flags, 0)) { pte_unmap(ptep); return -EFAULT; _