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Wed, 13 Nov 2019 10:17:27 +1100 (AEDT) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqemgate16.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 12 Nov 2019 15:16:27 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Tue, 12 Nov 2019 15:17:23 -0800 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 12 Nov 2019 15:17:23 -0800 Received: from [10.110.48.28] (10.124.1.5) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 12 Nov 2019 23:17:22 +0000 Subject: Re: [PATCH v3 08/23] vfio, mm: fix get_user_pages_remote() and FOLL_LONGTERM To: Dan Williams References: <20191112000700.3455038-1-jhubbard@nvidia.com> <20191112000700.3455038-9-jhubbard@nvidia.com> <20191112204338.GE5584@ziepe.ca> <0db36e86-b779-01af-77e7-469af2a2e19c@nvidia.com> From: John Hubbard X-Nvconfidentiality: public Message-ID: <85987617-9f6b-6bd3-fea2-9f2910d942bd@nvidia.com> Date: Tue, 12 Nov 2019 15:17:22 -0800 User-Agent: Mozilla/5.0 (X11; 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Miller" , Mike Kravetz Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 11/12/19 2:45 PM, Dan Williams wrote: > On Tue, Nov 12, 2019 at 2:43 PM John Hubbard wrote: >> >> On 11/12/19 12:43 PM, Jason Gunthorpe wrote: >> ... >>>> - } >>>> + ret = get_user_pages_remote(NULL, mm, vaddr, 1, flags | FOLL_LONGTERM, >>>> + page, vmas, NULL); >>>> + /* >>>> + * The lifetime of a vaddr_get_pfn() page pin is >>>> + * userspace-controlled. In the fs-dax case this could >>>> + * lead to indefinite stalls in filesystem operations. >>>> + * Disallow attempts to pin fs-dax pages via this >>>> + * interface. >>>> + */ >>>> + if (ret > 0 && vma_is_fsdax(vmas[0])) { >>>> + ret = -EOPNOTSUPP; >>>> + put_page(page[0]); >>>> } >>> >>> AFAIK this chunk is redundant now as it is some hack to emulate >>> FOLL_LONGTERM? So vmas can be deleted too. >> >> Let me first make sure I understand what Dan has in mind for the vma >> checking, in the other thread... > > It's not redundant relative to upstream which does not do anything the > FOLL_LONGTERM in the gup-slow path... but I have not looked at patches > 1-7 to see if something there made it redundant. > There is nothing in patches 1-7 that would make it redundant. About the only thing that you might find interesting in that subset is patch 4 ("mm: devmap: refactor 1-based refcounting for ZONE_DEVICE pages"), for devmap and ZONE_DEVICE interest. But it doesn't affect this discussion directly. thanks, -- John Hubbard NVIDIA