Re: [PATCH v3] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled

[Jason Gunthorpe]

On Mon, Aug 30, 2021 at 05:42:32PM +0800, Li Zhijian wrote:
> 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@xxxxxxxxxxxxxxx
> Fixes: 405506274922 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling")
> Signed-off-by: Li Zhijian <lizhijian@xxxxxxxxxxxxxx>
> 
> ---
> V3: adjust the checking order
> ---
>  mm/hmm.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Andrew, can you grab this please?

Thanks,
Jason