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[142.68.57.212]) by smtp.gmail.com with ESMTPSA id l13sm12836457qke.116.2020.03.12.07.24.29 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 12 Mar 2020 07:24:29 -0700 (PDT) Received: from jgg by mlx.ziepe.ca with local (Exim 4.90_1) (envelope-from ) id 1jCOlB-0006Wf-C8; Thu, 12 Mar 2020 11:24:29 -0300 Date: Thu, 12 Mar 2020 11:24:29 -0300 From: Jason Gunthorpe To: Ralph Campbell Cc: Jerome Glisse , Felix.Kuehling@amd.com, linux-mm@kvack.org, John Hubbard , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Christoph Hellwig , Philip Yang Subject: Re: [PATCH hmm 1/8] mm/hmm: add missing unmaps of the ptep during hmm_vma_handle_pte() Message-ID: <20200312142429.GL31668@ziepe.ca> References: <20200311183506.3997-1-jgg@ziepe.ca> <20200311183506.3997-2-jgg@ziepe.ca> <1cfdfdff-6d41-b73a-fe48-c7a10c221482@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1cfdfdff-6d41-b73a-fe48-c7a10c221482@nvidia.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Mar 11, 2020 at 06:28:30PM -0700, Ralph Campbell wrote: > > mm/hmm.c | 8 ++++++-- > > 1 file changed, 6 insertions(+), 2 deletions(-) > > > > diff --git a/mm/hmm.c b/mm/hmm.c > > index 72e5a6d9a41756..35f85424176d14 100644 > > +++ b/mm/hmm.c > > @@ -325,6 +325,7 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, > > } > > /* Report error for everything else */ > > + pte_unmap(ptep); > > *pfn = range->values[HMM_PFN_ERROR]; > > return -EFAULT; > > } else { > > @@ -339,10 +340,13 @@ static int hmm_vma_handle_pte(struct mm_walk *walk, unsigned long addr, > > if (pte_devmap(pte)) { > > hmm_vma_walk->pgmap = get_dev_pagemap(pte_pfn(pte), > > hmm_vma_walk->pgmap); > > - if (unlikely(!hmm_vma_walk->pgmap)) > > + if (unlikely(!hmm_vma_walk->pgmap)) { > > + pte_unmap(ptep); > > return -EBUSY; > > + } > > } else if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL) && pte_special(pte)) { > > if (!is_zero_pfn(pte_pfn(pte))) { > > + pte_unmap(ptep); > > *pfn = range->values[HMM_PFN_SPECIAL]; > > return -EFAULT; > > } > > @@ -437,7 +441,7 @@ static int hmm_vma_walk_pmd(pmd_t *pmdp, > > r = hmm_vma_handle_pte(walk, addr, end, pmdp, ptep, &pfns[i]); > > if (r) { > > - /* hmm_vma_handle_pte() did unmap pte directory */ > > + /* hmm_vma_handle_pte() did pte_unmap() */ > > hmm_vma_walk->last = addr; > > return r; > > } > > > > I think there is a case where hmm_vma_handle_pte() is called, a fault is requested, > pte_unmap() and hmm_vma_walk_hole_() are called, the latter returns zero (the fault > was handled OK) Not quite, hmm_vma_walk_hole_() never returns 0 if called with fault: return (fault || write_fault) ? -EBUSY : 0; And all the call sites of hmm_vma_walk_hole_() in hmm_vma_handle_pte() are structured as: if (fault || write_fault) goto fault; fault: return hmm_vma_walk_hole_(addr, end, fault, write_fault, walk); So, it never returns 0. I already made a patch making this less twisty while fixing something else: https://github.com/jgunthorpe/linux/commit/078e10ca5919f2c263c245784fb5fe63ddbb61f4 Thanks, Jason