This is a note to let you know that I've just added the patch titled mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled to the 5.14-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mm-hmm-bypass-devmap-pte-when-all-pfn-requested-flags-are-fulfilled.patch and it can be found in the queue-5.14 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 4b42fb213678d2b6a9eeea92a9be200f23e49583 Mon Sep 17 00:00:00 2001 From: Li Zhijian <lizhijian@xxxxxxxxxxxxxx> Date: Wed, 8 Sep 2021 18:10:02 -0700 Subject: mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled From: Li Zhijian <lizhijian@xxxxxxxxxxxxxx> commit 4b42fb213678d2b6a9eeea92a9be200f23e49583 upstream. Previously, we noticed the one rpma example was failed[1] since commit 36f30e486dce ("IB/core: Improve ODP to use hmm_range_fault()"), 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(). Link: https://github.com/pmem/rpma/issues/1142 [1] Link: https://lkml.kernel.org/r/20210830094232.203029-1-lizhijian@xxxxxxxxxxxxxx Fixes: 405506274922 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling") Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxxxxx> Reviewed-by: Christoph Hellwig <hch@xxxxxx> Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- mm/hmm.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/mm/hmm.c +++ b/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; Patches currently in stable-queue which might be from lizhijian@xxxxxxxxxxxxxx are queue-5.14/mm-hmm-bypass-devmap-pte-when-all-pfn-requested-flags-are-fulfilled.patch queue-5.14/selftests-bpf-enlarge-select-timeout-for-test_maps.patch