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[142.162.113.129]) by smtp.gmail.com with ESMTPSA id c2sm3754947qte.22.2021.08.27.09.28.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Aug 2021 09:28:52 -0700 (PDT) Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1mJeiq-005jqI-8p; Fri, 27 Aug 2021 13:28:52 -0300 Date: Fri, 27 Aug 2021 13:28:52 -0300 From: Jason Gunthorpe To: Li Zhijian Cc: linux-mm@kvack.org, linux-rdma@vger.kernel.org, akpm@linux-foundation.org, jglisse@redhat.com, yishaih@nvidia.com, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm/hmm: bypass devmap pte when all pfn requested flags are fulfilled Message-ID: <20210827162852.GL1200268@ziepe.ca> References: <20210827144500.2148-1-lizhijian@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210827144500.2148-1-lizhijian@cn.fujitsu.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 27, 2021 at 10:45:00PM +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@vger.kernel.org > Signed-off-by: Li Zhijian You need to add a Fixes: 405506274922 ("mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling") > diff --git a/mm/hmm.c b/mm/hmm.c > index fad6be2bf072..4766bdefb6c3 100644 > +++ 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; I liked your ealier version better where this was added to the pte_special test - logically this is about disambiguating the pte_special and the devmap case as they are different things. Jason