From patchwork Wed Aug 21 04:07:26 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Hubbard X-Patchwork-Id: 11105409 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7CA8A1805 for ; Wed, 21 Aug 2019 04:07:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 503B42339D for ; Wed, 21 Aug 2019 04:07:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="RJvMkiak" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727529AbfHUEHk (ORCPT ); Wed, 21 Aug 2019 00:07:40 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:18936 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727481AbfHUEHh (ORCPT ); Wed, 21 Aug 2019 00:07:37 -0400 Received: from hqpgpgate102.nvidia.com (Not Verified[216.228.121.13]) by hqemgate15.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 20 Aug 2019 21:07:35 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate102.nvidia.com (PGP Universal service); Tue, 20 Aug 2019 21:07:34 -0700 X-PGP-Universal: processed; by hqpgpgate102.nvidia.com on Tue, 20 Aug 2019 21:07:34 -0700 Received: from HQMAIL110.nvidia.com (172.18.146.15) by HQMAIL101.nvidia.com (172.20.187.10) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Wed, 21 Aug 2019 04:07:33 +0000 Received: from HQMAIL105.nvidia.com (172.20.187.12) by hqmail110.nvidia.com (172.18.146.15) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Wed, 21 Aug 2019 04:07:33 +0000 Received: from hqnvemgw02.nvidia.com (172.16.227.111) by HQMAIL105.nvidia.com (172.20.187.12) with Microsoft SMTP Server (TLS) id 15.0.1473.3 via Frontend Transport; Wed, 21 Aug 2019 04:07:33 +0000 Received: from blueforge.nvidia.com (Not Verified[10.110.48.28]) by hqnvemgw02.nvidia.com with Trustwave SEG (v7,5,8,10121) id ; Tue, 20 Aug 2019 21:07:33 -0700 From: John Hubbard To: Andrew Morton CC: Christoph Hellwig , Dan Williams , Dave Chinner , Ira Weiny , Jan Kara , Jason Gunthorpe , =?utf-8?b?SsOpcsO0bWUgR2xpc3Nl?= , Vlastimil Babka , LKML , , , , John Hubbard , "Michal Hocko" Subject: [PATCH v2 2/3] mm/gup: introduce FOLL_PIN flag for get_user_pages() Date: Tue, 20 Aug 2019 21:07:26 -0700 Message-ID: <20190821040727.19650-3-jhubbard@nvidia.com> X-Mailer: git-send-email 2.22.1 In-Reply-To: <20190821040727.19650-1-jhubbard@nvidia.com> References: <20190821040727.19650-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1566360455; bh=vXTR5X576mO9cmS9xl7R7KR9+U7vJV56myFxKqNBdTs=; h=X-PGP-Universal:From:To:CC:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:X-NVConfidentiality: Content-Transfer-Encoding:Content-Type; b=RJvMkiak0tzTwcCSvp33yG5WfqF9U4NOaOCVMZ5uYvRXjYdZi+/K97QTPP5ZrURvK 6pM2OKGy8zZc3UvMYlHiZkLqER5IcaSP6qs5SX9frmczNM5fEsm3U952K6yieeJwc3 51cP+GTW5WHrvhwdEl1aAW5PFlfR8EpZTqS/ZpX6Xbm+WNCXL24HWIcIdXQpMsUIzE D0mk89PmNnLoQ/PfiZYEPVRLmXeFy0q8pSqg+ZRSmJrlnOZOlOeqEm+z1UmZtcCw4b cuYh/n9t7lihEjNuAsyxPqaxrYCf5IK9OEPa4qnFsT2qQNmjWR/kFrIpk0teDK7KAa C/pGQVF0bsKTQ== Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org As explained in the newly added documentation for FOLL_PIN and FOLL_LONGTERM, in every case where vaddr_pin_pages() is required, FOLL_PIN must be set. That reason, plus a desire to keep FOLL_PIN an internal (to get_user_pages() and follow_page()) detail, is why vaddr_pin_pages() sets FOLL_PIN. FOLL_LONGTERM, on the other hand, in only set in *some* cases, but not all. For that reason, this patch moves the setting of FOLL_LONGTERM out to the caller. Also add fairly extensive documentation of the meaning and use of both FOLL_PIN and FOLL_LONGTERM. Thanks to Jan Kara and Vlastimil Babka for explaining the 4 cases in this documentation. (I've reworded it and expanded on it slightly.) The motivation behind moving away from "bare" get_user_pages() calls is described in more detail in commit fc1d8e7cca2d ("mm: introduce put_user_page*(), placeholder versions"). Cc: Vlastimil Babka Cc: Jan Kara Cc: Michal Hocko Cc: Ira Weiny Signed-off-by: John Hubbard --- drivers/infiniband/core/umem.c | 1 + include/linux/mm.h | 56 ++++++++++++++++++++++++++++++---- mm/gup.c | 2 +- 3 files changed, 52 insertions(+), 7 deletions(-) diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c index e69eecb0023f..d84f1bfb8d21 100644 --- a/drivers/infiniband/core/umem.c +++ b/drivers/infiniband/core/umem.c @@ -300,6 +300,7 @@ struct ib_umem *ib_umem_get(struct ib_udata *udata, unsigned long addr, while (npages) { down_read(&mm->mmap_sem); + gup_flags |= FOLL_LONGTERM; ret = vaddr_pin_pages(cur_base, min_t(unsigned long, npages, PAGE_SIZE / sizeof (struct page *)), diff --git a/include/linux/mm.h b/include/linux/mm.h index bc675e94ddf8..6e7de424bf5e 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2644,6 +2644,8 @@ static inline vm_fault_t vmf_error(int err) struct page *follow_page(struct vm_area_struct *vma, unsigned long address, unsigned int foll_flags); +/* Flags for follow_page(), get_user_pages ("GUP"), and vaddr_pin_pages(): */ + #define FOLL_WRITE 0x01 /* check pte is writable */ #define FOLL_TOUCH 0x02 /* mark page accessed */ #define FOLL_GET 0x04 /* do get_page on page */ @@ -2663,13 +2665,15 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, #define FOLL_ANON 0x8000 /* don't do file mappings */ #define FOLL_LONGTERM 0x10000 /* mapping lifetime is indefinite: see below */ #define FOLL_SPLIT_PMD 0x20000 /* split huge pmd before returning */ +#define FOLL_PIN 0x40000 /* pages must be released via put_user_page() */ /* - * NOTE on FOLL_LONGTERM: + * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each + * other. Here is what they mean, and how to use them: * * FOLL_LONGTERM indicates that the page will be held for an indefinite time - * period _often_ under userspace control. This is contrasted with - * iov_iter_get_pages() where usages which are transient. + * period _often_ under userspace control. This is in contrast to + * iov_iter_get_pages(), where usages which are transient. * * FIXME: For pages which are part of a filesystem, mappings are subject to the * lifetime enforced by the filesystem and we need guarantees that longterm @@ -2684,11 +2688,51 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, * Currently only get_user_pages() and get_user_pages_fast() support this flag * and calls to get_user_pages_[un]locked are specifically not allowed. This * is due to an incompatibility with the FS DAX check and - * FAULT_FLAG_ALLOW_RETRY + * FAULT_FLAG_ALLOW_RETRY. * - * In the CMA case: longterm pins in a CMA region would unnecessarily fragment - * that region. And so CMA attempts to migrate the page before pinning when + * In the CMA case: long term pins in a CMA region would unnecessarily fragment + * that region. And so, CMA attempts to migrate the page before pinning, when * FOLL_LONGTERM is specified. + * + * FOLL_PIN indicates that a special kind of tracking (not just page->_refcount, + * but an additional pin counting system) will be invoked. This is intended for + * anything that gets a page reference and then touches page data (for example, + * Direct IO). This lets the filesystem know that some non-file-system entity is + * potentially changing the pages' data. FOLL_PIN pages must be released, + * ultimately, by a call to put_user_page(). Typically that will be via one of + * the vaddr_unpin_pages() variants. + * + * FIXME: note that this special tracking is not in place yet. However, the + * pages should still be released by put_user_page(). + * + * When and where to use each flag: + * + * CASE 1: Direct IO (DIO). There are GUP references to pages that are serving + * as DIO buffers. These buffers are needed for a relatively short time (so they + * are not "long term"). No special synchronization with page_mkclean() or + * munmap() is provided. Therefore, flags to set at the call site are: + * + * FOLL_PIN + * + * CASE 2: RDMA. There are GUP references to pages that are serving as DMA + * buffers. These buffers are needed for a long time ("long term"). No special + * synchronization with page_mkclean() or munmap() is provided. Therefore, flags + * to set at the call site are: + * + * FOLL_PIN | FOLL_LONGTERM + * + * There is also a special case when the pages are DAX pages: in addition to the + * above flags, the caller needs a file lease. This is provided via the struct + * vaddr_pin argument to vaddr_pin_pages(). + * + * CASE 3: ODP (Mellanox/Infiniband On Demand Paging: the hardware supports + * replayable page faulting). There are GUP references to pages serving as DMA + * buffers. For ODP, MMU notifiers are used to synchronize with page_mkclean() + * and munmap(). Therefore, normal GUP calls are sufficient, so neither flag + * needs to be set. + * + * CASE 4: pinning for struct page manipulation only. Here, normal GUP calls are + * sufficient, so neither flag needs to be set. */ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags) diff --git a/mm/gup.c b/mm/gup.c index e49096d012ea..ba316d960d7a 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2490,7 +2490,7 @@ long vaddr_pin_pages(unsigned long addr, unsigned long nr_pages, { long ret; - gup_flags |= FOLL_LONGTERM; + gup_flags |= FOLL_PIN; if (!vaddr_pin || (!vaddr_pin->mm && !vaddr_pin->f_owner)) return -EINVAL;