From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4A6FCA9ECE for ; Thu, 31 Oct 2019 23:15:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A77192080F for ; Thu, 31 Oct 2019 23:15:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728779AbfJaXPP (ORCPT ); Thu, 31 Oct 2019 19:15:15 -0400 Received: from mga01.intel.com ([192.55.52.88]:52440 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727423AbfJaXPO (ORCPT ); Thu, 31 Oct 2019 19:15:14 -0400 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga101.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 31 Oct 2019 16:15:07 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.68,253,1569308400"; d="scan'208";a="225867978" Received: from iweiny-desk2.sc.intel.com ([10.3.52.157]) by fmsmga004.fm.intel.com with ESMTP; 31 Oct 2019 16:15:04 -0700 Date: Thu, 31 Oct 2019 16:15:04 -0700 From: Ira Weiny To: John Hubbard Cc: Andrew Morton , Al Viro , Alex Williamson , Benjamin Herrenschmidt , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , Christoph Hellwig , Dan Williams , Daniel Vetter , Dave Chinner , David Airlie , "David S . Miller" , Jan Kara , Jason Gunthorpe , Jens Axboe , Jonathan Corbet , =?iso-8859-1?B?Suly9G1l?= Glisse , Magnus Karlsson , Mauro Carvalho Chehab , Michael Ellerman , Michal Hocko , Mike Kravetz , Paul Mackerras , Shuah Khan , Vlastimil Babka , bpf@vger.kernel.org, dri-devel@lists.freedesktop.org, kvm@vger.kernel.org, linux-block@vger.kernel.org, linux-doc@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, netdev@vger.kernel.org, linux-mm@kvack.org, LKML Subject: Re: [PATCH 05/19] mm/gup: introduce pin_user_pages*() and FOLL_PIN Message-ID: <20191031231503.GF14771@iweiny-DESK2.sc.intel.com> References: <20191030224930.3990755-1-jhubbard@nvidia.com> <20191030224930.3990755-6-jhubbard@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030224930.3990755-6-jhubbard@nvidia.com> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Oct 30, 2019 at 03:49:16PM -0700, John Hubbard wrote: > Introduce pin_user_pages*() variations of get_user_pages*() calls, > and also pin_longterm_pages*() variations. > > These variants all set FOLL_PIN, which is also introduced, and > basically documented. (An upcoming patch provides more extensive > documentation.) The second set (pin_longterm*) also sets > FOLL_LONGTERM: > > pin_user_pages() > pin_user_pages_remote() > pin_user_pages_fast() > > pin_longterm_pages() > pin_longterm_pages_remote() > pin_longterm_pages_fast() > > All pages that are pinned via the above calls, must be unpinned via > put_user_page(). > > The underlying rules are: > > * These are gup-internal flags, so the call sites should not directly > set FOLL_PIN nor FOLL_LONGTERM. That behavior is enforced with > assertions, for the new FOLL_PIN flag. However, for the pre-existing > FOLL_LONGTERM flag, which has some call sites that still directly > set FOLL_LONGTERM, there is no assertion yet. > > * Call sites that want to indicate that they are going to do DirectIO > ("DIO") or something with similar characteristics, should call a > get_user_pages()-like wrapper call that sets FOLL_PIN. These wrappers > will: > * Start with "pin_user_pages" instead of "get_user_pages". That > makes it easy to find and audit the call sites. > * Set FOLL_PIN > > * For pages that are received via FOLL_PIN, those pages must be returned > via put_user_page(). > > Signed-off-by: John Hubbard > --- > include/linux/mm.h | 53 ++++++++- > mm/gup.c | 284 +++++++++++++++++++++++++++++++++++++++++---- > 2 files changed, 311 insertions(+), 26 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index cc292273e6ba..62c838a3e6c7 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -1526,9 +1526,23 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas, int *locked); > +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked); > +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked); > long get_user_pages(unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas); > +long pin_user_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas); > +long pin_longterm_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas); > long get_user_pages_locked(unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, int *locked); > long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > @@ -1536,6 +1550,10 @@ long get_user_pages_unlocked(unsigned long start, unsigned long nr_pages, > > int get_user_pages_fast(unsigned long start, int nr_pages, > unsigned int gup_flags, struct page **pages); > +int pin_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages); > +int pin_longterm_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages); > > int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc); > int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc, > @@ -2594,13 +2612,15 @@ 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 > @@ -2615,11 +2635,32 @@ 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. In contrast to FOLL_GET (whose pages > + * are released via put_page()), FOLL_PIN pages must be released, ultimately, by > + * a call to put_user_page(). > + * > + * FOLL_PIN is similar to FOLL_GET: both of these pin pages. They use different > + * and separate refcounting mechanisms, however, and that means that each has > + * its own acquire and release mechanisms: > + * > + * FOLL_GET: get_user_pages*() to acquire, and put_page() to release. > + * > + * FOLL_PIN: pin_user_pages*() or pin_longterm_pages*() to acquire, and > + * put_user_pages to release. > + * > + * FOLL_PIN and FOLL_GET are mutually exclusive. You mean the flags are mutually exclusive for any single call, correct? Because my first thought was that you meant that a page which was pin'ed can't be "got". Which I don't think is true or necessary... > + * > + * Please see Documentation/vm/pin_user_pages.rst for more information. NIT: I think we should include this file as part of this patch... > */ > > 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 8fb0d9cdfaf5..8694bc7b3df3 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -179,6 +179,10 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, > spinlock_t *ptl; > pte_t *ptep, pte; > > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) == > + (FOLL_PIN | FOLL_GET))) > + return ERR_PTR(-EINVAL); > retry: > if (unlikely(pmd_bad(*pmd))) > return no_page_table(vma, flags); > @@ -790,7 +794,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, > > start = untagged_addr(start); > > - VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET)); > + VM_BUG_ON(!!pages != !!(gup_flags & (FOLL_GET | FOLL_PIN))); > > /* > * If FOLL_FORCE is set then do not force a full fault as the hinting > @@ -1014,7 +1018,16 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk, > BUG_ON(*locked != 1); > } > > - if (pages) > + /* > + * FOLL_PIN and FOLL_GET are mutually exclusive. Traditional behavior > + * is to set FOLL_GET if the caller wants pages[] filled in (but has > + * carelessly failed to specify FOLL_GET), so keep doing that, but only > + * for FOLL_GET, not for the newer FOLL_PIN. > + * > + * FOLL_PIN always expects pages to be non-null, but no need to assert > + * that here, as any failures will be obvious enough. > + */ > + if (pages && !(flags & FOLL_PIN)) > flags |= FOLL_GET; > > pages_done = 0; > @@ -1133,6 +1146,12 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk, > * is written to, set_page_dirty (or set_page_dirty_lock, as appropriate) must > * be called after the page is finished with, and before put_page is called. > * > + * A note on gup_flags: FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. > + * That's in order to help avoid mismatches when releasing pages: > + * get_user_pages*() pages must be released via put_page(), while > + * pin_user_pages*() pages must be released via put_user_page(). > + * > * get_user_pages is typically used for fewer-copy IO operations, to get a > * handle on the memory by some means other than accesses via the user virtual > * addresses. The pages may be submitted for DMA to devices or accessed via > @@ -1151,6 +1170,14 @@ long get_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas, int *locked) > { > + /* > + * As detailed above, FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the > + * caller, so enforce that with an assertion: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return -EINVAL; > + > /* > * FIXME: Current FOLL_LONGTERM behavior is incompatible with > * FAULT_FLAG_ALLOW_RETRY because of the FS DAX check requirement on > @@ -1603,11 +1630,25 @@ static __always_inline long __gup_longterm_locked(struct task_struct *tsk, > * and mm being operated on are the current task's and don't allow > * passing of a locked parameter. We also obviously don't pass > * FOLL_REMOTE in here. > + * > + * A note on gup_flags: FOLL_PIN should only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. > + * That's in order to help avoid mismatches when releasing pages: > + * get_user_pages*() pages must be released via put_page(), while > + * pin_user_pages*() pages must be released via put_user_page(). Rather than put this here should we put it next to the definition of FOLL_PIN? Because now we have this text 2x... :-/ > */ > long get_user_pages(unsigned long start, unsigned long nr_pages, > unsigned int gup_flags, struct page **pages, > struct vm_area_struct **vmas) > { > + /* > + * As detailed above, FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the > + * caller, so enforce that with an assertion: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return -EINVAL; > + > return __gup_longterm_locked(current, current->mm, start, nr_pages, > pages, vmas, gup_flags | FOLL_TOUCH); > } > @@ -2366,24 +2407,9 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, > return ret; > } > > -/** > - * get_user_pages_fast() - pin user pages in memory > - * @start: starting user address > - * @nr_pages: number of pages from start to pin > - * @gup_flags: flags modifying pin behaviour > - * @pages: array that receives pointers to the pages pinned. > - * Should be at least nr_pages long. > - * > - * Attempt to pin user pages in memory without taking mm->mmap_sem. > - * If not successful, it will fall back to taking the lock and > - * calling get_user_pages(). > - * > - * Returns number of pages pinned. This may be fewer than the number > - * requested. If nr_pages is 0 or negative, returns 0. If no pages > - * were pinned, returns -errno. > - */ > -int get_user_pages_fast(unsigned long start, int nr_pages, > - unsigned int gup_flags, struct page **pages) > +static int internal_get_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, > + struct page **pages) > { > unsigned long addr, len, end; > int nr = 0, ret = 0; > @@ -2428,4 +2454,222 @@ int get_user_pages_fast(unsigned long start, int nr_pages, > > return ret; > } > + > +/** > + * get_user_pages_fast() - pin user pages in memory > + * @start: starting user address > + * @nr_pages: number of pages from start to pin > + * @gup_flags: flags modifying pin behaviour > + * @pages: array that receives pointers to the pages pinned. > + * Should be at least nr_pages long. > + * > + * Attempt to pin user pages in memory without taking mm->mmap_sem. > + * If not successful, it will fall back to taking the lock and > + * calling get_user_pages(). > + * > + * A note on gup_flags: FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the caller. > + * That's in order to help avoid mismatches when releasing pages: > + * get_user_pages*() pages must be released via put_page(), while > + * pin_user_pages*() pages must be released via put_user_page(). > + * > + * Returns number of pages pinned. This may be fewer than the number requested. > + * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns > + * -errno. > + */ > +int get_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages) > +{ > + /* > + * As detailed above, FOLL_PIN must only be set internally by the > + * pin_user_page*() and pin_longterm_*() APIs, never directly by the > + * caller, so enforce that: > + */ > + if (WARN_ON_ONCE(gup_flags & FOLL_PIN)) > + return -EINVAL; > + > + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > +} > EXPORT_SYMBOL_GPL(get_user_pages_fast); > + > +/** > + * pin_user_pages_fast() - pin user pages in memory without taking locks > + * > + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN is set. See > + * get_user_pages_fast() for documentation on the function arguments, because > + * the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +int pin_user_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_PIN; > + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > +} > +EXPORT_SYMBOL_GPL(pin_user_pages_fast); > + > +/** > + * pin_longterm_pages_fast() - pin user pages in memory without taking locks > + * > + * Nearly the same as get_user_pages_fast(), except that FOLL_PIN and > + * FOLL_LONGTERM are set. See get_user_pages_fast() for documentation on the > + * function arguments, because the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, > + * typically by a non-CPU device, and we cannot be sure that waiting for a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) of the FOLL_PIN > + * documentation. > + */ > +int pin_longterm_pages_fast(unsigned long start, int nr_pages, > + unsigned int gup_flags, struct page **pages) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= (FOLL_PIN | FOLL_LONGTERM); > + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); > +} > +EXPORT_SYMBOL_GPL(pin_longterm_pages_fast); > + > +/** > + * pin_user_pages_remote() - pin pages for (typically) use by Direct IO, and > + * return the pages to the user. > + * > + * Nearly the same as get_user_pages_remote(), except that FOLL_PIN is set. See > + * get_user_pages_remote() for documentation on the function arguments, because > + * the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +long pin_user_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN; > + > + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > + locked, gup_flags); > +} > +EXPORT_SYMBOL(pin_user_pages_remote); > + > +/** > + * pin_longterm_pages_remote() - pin pages for (typically) use by Direct IO, and > + * return the pages to the user. > + * > + * Nearly the same as get_user_pages_remote(), but note that FOLL_TOUCH is not > + * set, and FOLL_PIN and FOLL_LONGTERM are set. See get_user_pages_remote() for > + * documentation on the function arguments, because the arguments here are > + * identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, > + * typically by a non-CPU device, and we cannot be sure that waiting for a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) in > + * Documentation/vm/pin_user_pages.rst. > + */ > +long pin_longterm_pages_remote(struct task_struct *tsk, struct mm_struct *mm, > + unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas, int *locked) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + /* > + * FIXME: as noted in the get_user_pages_remote() implementation, it > + * is not yet possible to safely set FOLL_LONGTERM here. FOLL_LONGTERM > + * needs to be set, but for now the best we can do is a "TODO" item. > + */ Wait? Why can't we set FOLL_LONGTERM here? pin_* are new calls which are not used yet right? You set it in the other new pin_* functions? Ira > + gup_flags |= FOLL_REMOTE | FOLL_PIN; > + > + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas, > + locked, gup_flags); > +} > +EXPORT_SYMBOL(pin_longterm_pages_remote); > + > +/** > + * pin_user_pages() - pin user pages in memory for use by other devices > + * > + * Nearly the same as get_user_pages(), except that FOLL_TOUCH is not set, and > + * FOLL_PIN is set. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for details. > + * > + * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rst. It > + * is NOT intended for Case 2 (RDMA: long-term pins). > + */ > +long pin_user_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_PIN; > + return __gup_longterm_locked(current, current->mm, start, nr_pages, > + pages, vmas, gup_flags); > +} > +EXPORT_SYMBOL(pin_user_pages); > + > +/** > + * pin_longterm_pages() - pin user pages in memory for long-term use (RDMA, > + * typically) > + * > + * Nearly the same as get_user_pages(), except that FOLL_PIN and FOLL_LONGTERM > + * are set. See get_user_pages_fast() for documentation on the function > + * arguments, because the arguments here are identical. > + * > + * FOLL_PIN means that the pages must be released via put_user_page(). Please > + * see Documentation/vm/pin_user_pages.rst for further details. > + * > + * FOLL_LONGTERM means that the pages are being pinned for "long term" use, > + * typically by a non-CPU device, and we cannot be sure that waiting for a > + * pinned page to become unpin will be effective. > + * > + * This is intended for Case 2 (RDMA: long-term pins) in > + * Documentation/vm/pin_user_pages.rst. > + */ > +long pin_longterm_pages(unsigned long start, unsigned long nr_pages, > + unsigned int gup_flags, struct page **pages, > + struct vm_area_struct **vmas) > +{ > + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ > + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) > + return -EINVAL; > + > + gup_flags |= FOLL_PIN | FOLL_LONGTERM; > + return __gup_longterm_locked(current, current->mm, start, nr_pages, > + pages, vmas, gup_flags); > +} > +EXPORT_SYMBOL(pin_longterm_pages); > -- > 2.23.0 >