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Wed, 13 Nov 2019 13:09:17 +1100 (AEDT) Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqemgate15.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 12 Nov 2019 18:09:09 -0800 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Tue, 12 Nov 2019 18:09:09 -0800 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Tue, 12 Nov 2019 18:09:09 -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; Wed, 13 Nov 2019 02:09:09 +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> <20191112234250.GA19615@ziepe.ca> <28355eb0-4ee5-3418-b430-59302d15b478@nvidia.com> From: John Hubbard X-Nvconfidentiality: public Message-ID: Date: Tue, 12 Nov 2019 18:09:08 -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 5:35 PM, Dan Williams wrote: > On Tue, Nov 12, 2019 at 5:08 PM John Hubbard wrote: >> >> On 11/12/19 4:58 PM, Dan Williams wrote: >> ... >>>>> 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. >>>> >>>> Oh, the hunk John had below for get_user_pages_remote() also needs to >>>> call __gup_longterm_locked() when FOLL_LONGTERM is specified, then >>>> that calls check_dax_vmas() which duplicates the vma_is_fsdax() check >>>> above. >>> >>> Oh true, good eye. It is redundant if it does additionally call >>> __gup_longterm_locked(), and it needs to do that otherwises it undoes >>> the CMA migration magic that Aneesh added. >>> >> >> OK. So just to be clear, I'll be removing this from the patch: >> >> /* >> * 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]); >> } >> >> (and the declaration of "vmas", as well). > > ...and add a call to __gup_longterm_locked internal to > get_user_pages_remote(), right? > Yes, and thanks for double-checking. I think I got a little dizzy following the call stack there. :) And now I see that this also affects the implementation of pin_longterm_pages_remote(), because that will need the same logic that get_user_pages_remote() has. thanks, -- John Hubbard NVIDIA