From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: [patch 043/155] mm/gup: track FOLL_PIN pages Date: Wed, 01 Apr 2020 21:05:29 -0700 Message-ID: <20200402040529.wHKICHtvB%akpm@linux-foundation.org> References: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Reply-To: linux-kernel@vger.kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Return-path: Received: from mail.kernel.org ([198.145.29.99]:52902 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725789AbgDBEFd (ORCPT ); Thu, 2 Apr 2020 00:05:33 -0400 In-Reply-To: <20200401210155.09e3b9742e1c6e732f5a7250@linux-foundation.org> Sender: mm-commits-owner@vger.kernel.org List-Id: mm-commits@vger.kernel.org To: akpm@linux-foundation.org, corbet@lwn.net, dan.j.williams@intel.com, david@fromorbit.com, hch@infradead.org, imbrenda@linux.ibm.com, ira.weiny@intel.com, jack@suse.cz, jgg@ziepe.ca, jglisse@redhat.com, jhubbard@nvidia.com, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, mhocko@suse.com, mike.kravetz@oracle.com, mm-commits@vger.kernel.org, shuah@kernel.org, torvalds@linux-foundation.org, vbabka@suse.cz, viro@zeniv.linux.org.uk, willy@infradead.org =46rom: John Hubbard Subject: mm/gup: track FOLL_PIN pages Add tracking of pages that were pinned via FOLL_PIN. This tracking is implemented via overloading of page->_refcount: pins are added by adding GUP_PIN_COUNTING_BIAS (1024) to the refcount. This provides a fuzzy indication of pinning, and it can have false positives (and that's OK).=20 Please see the pre-existing Documentation/core-api/pin_user_pages.rst for details. As mentioned in pin_user_pages.rst, callers who effectively set FOLL_PIN (typically via pin_user_pages*()) are required to ultimately free such pages via unpin_user_page(). Please also note the limitation, discussed in pin_user_pages.rst under the "TODO: for 1GB and larger huge pages" section. (That limitation will be removed in a following patch.) The effect of a FOLL_PIN flag is similar to that of FOLL_GET, and may be thought of as "FOLL_GET for DIO and/or RDMA use". Pages that have been pinned via FOLL_PIN are identifiable via a new function call: bool page_maybe_dma_pinned(struct page *page); What to do in response to encountering such a page, is left to later patchsets. There is discussion about this in [1], [2], [3], and [4]. This also changes a BUG_ON(), to a WARN_ON(), in follow_page_mask(). [1] Some slow progress on get_user_pages() (Apr 2, 2019): https://lwn.net/Articles/784574/ [2] DMA and get_user_pages() (LPC: Dec 12, 2018): https://lwn.net/Articles/774411/ [3] The trouble with get_user_pages() (Apr 30, 2018): https://lwn.net/Articles/753027/ [4] LWN kernel index: get_user_pages(): https://lwn.net/Kernel/Index/#Memory_management-get_user_pages [jhubbard@nvidia.com: add kerneldoc] Link: http://lkml.kernel.org/r/20200307021157.235726-1-jhubbard@nvidia.com [imbrenda@linux.ibm.com: if pin fails, we need to unpin, a simple put_page = will not be enough] Link: http://lkml.kernel.org/r/20200306132537.783769-2-imbrenda@linux.ibm= .com [akpm@linux-foundation.org: fix put_compound_head defined but not used] Link: http://lkml.kernel.org/r/20200211001536.1027652-7-jhubbard@nvidia.com Signed-off-by: John Hubbard Signed-off-by: Claudio Imbrenda Reviewed-by: Jan Kara Acked-by: Kirill A. Shutemov Suggested-by: Jan Kara Suggested-by: J=C3=A9r=C3=B4me Glisse Cc: Ira Weiny Cc: "Matthew Wilcox (Oracle)" Cc: Al Viro Cc: Christoph Hellwig Cc: Dan Williams Cc: Dave Chinner Cc: Jason Gunthorpe Cc: Jonathan Corbet Cc: Michal Hocko Cc: Mike Kravetz Cc: Shuah Khan Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- Documentation/core-api/pin_user_pages.rst | 6=20 include/linux/mm.h | 84 ++++- mm/gup.c | 312 ++++++++++++++++---- mm/huge_memory.c | 29 + mm/hugetlb.c | 54 ++- 5 files changed, 380 insertions(+), 105 deletions(-) --- a/Documentation/core-api/pin_user_pages.rst~mm-gup-track-foll_pin-pages +++ a/Documentation/core-api/pin_user_pages.rst @@ -173,8 +173,8 @@ CASE 4: Pinning for struct page manipula ------------------------------------------------- Here, normal GUP calls are sufficient, so neither flag needs to be set. =20 -page_dma_pinned(): the whole point of pinning -=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D +page_maybe_dma_pinned(): the whole point of pinning +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D =20 The whole point of marking pages as "DMA-pinned" or "gup-pinned" is to be = able to query, "is this page DMA-pinned?" That allows code such as page_mkclean= () @@ -186,7 +186,7 @@ and debates (see the References at the e here: fill in the details once that's worked out. Meanwhile, it's safe to = say that having this available: :: =20 - static inline bool page_dma_pinned(struct page *page) + static inline bool page_maybe_dma_pinned(struct page *page) =20 ...is a prerequisite to solving the long-running gup+DMA problem. =20 --- a/include/linux/mm.h~mm-gup-track-foll_pin-pages +++ a/include/linux/mm.h @@ -1001,6 +1001,8 @@ static inline void get_page(struct page page_ref_inc(page); } =20 +bool __must_check try_grab_page(struct page *page, unsigned int flags); + static inline __must_check bool try_get_page(struct page *page) { page =3D compound_head(page); @@ -1029,29 +1031,79 @@ static inline void put_page(struct page __put_page(page); } =20 -/** - * unpin_user_page() - release a gup-pinned page - * @page: pointer to page to be released +/* + * GUP_PIN_COUNTING_BIAS, and the associated functions that use it, overlo= ad + * the page's refcount so that two separate items are tracked: the origina= l page + * reference count, and also a new count of how many pin_user_pages() call= s were + * made against the page. ("gup-pinned" is another term for the latter). + * + * With this scheme, pin_user_pages() becomes special: such pages are mark= ed as + * distinct from normal pages. As such, the unpin_user_page() call (and its + * variants) must be used in order to release gup-pinned pages. + * + * Choice of value: + * + * By making GUP_PIN_COUNTING_BIAS a power of two, debugging of page refer= ence + * counts with respect to pin_user_pages() and unpin_user_page() becomes + * simpler, due to the fact that adding an even power of two to the page + * refcount has the effect of using only the upper N bits, for the code th= at + * counts up using the bias value. This means that the lower bits are left= for + * the exclusive use of the original code that increments and decrements b= y one + * (or at least, by much smaller values than the bias value). + * + * Of course, once the lower bits overflow into the upper bits (and this is + * OK, because subtraction recovers the original values), then visual insp= ection + * no longer suffices to directly view the separate counts. However, for n= ormal + * applications that don't have huge page reference counts, this won't be = an + * issue. * - * Pages that were pinned via pin_user_pages*() must be released via either - * unpin_user_page(), or one of the unpin_user_pages*() routines. This is = so - * that eventually such pages can be separately tracked and uniquely handl= ed. In - * particular, interactions with RDMA and filesystems need special handlin= g. - * - * unpin_user_page() and put_page() are not interchangeable, despite this = early - * implementation that makes them look the same. unpin_user_page() calls m= ust - * be perfectly matched up with pin*() calls. + * Locking: the lockless algorithm described in page_cache_get_speculative= () + * and page_cache_gup_pin_speculative() provides safe operation for + * get_user_pages and page_mkclean and other calls that race to set up page + * table entries. */ -static inline void unpin_user_page(struct page *page) -{ - put_page(page); -} +#define GUP_PIN_COUNTING_BIAS (1U << 10) =20 +void unpin_user_page(struct page *page); void unpin_user_pages_dirty_lock(struct page **pages, unsigned long npages, bool make_dirty); - void unpin_user_pages(struct page **pages, unsigned long npages); =20 +/** + * page_maybe_dma_pinned() - report if a page is pinned for DMA. + * + * This function checks if a page has been pinned via a call to + * pin_user_pages*(). + * + * For non-huge pages, the return value is partially fuzzy: false is not f= uzzy, + * because it means "definitely not pinned for DMA", but true means "proba= bly + * pinned for DMA, but possibly a false positive due to having at least + * GUP_PIN_COUNTING_BIAS worth of normal page references". + * + * False positives are OK, because: a) it's unlikely for a page to get tha= t many + * refcounts, and b) all the callers of this routine are expected to be ab= le to + * deal gracefully with a false positive. + * + * For more information, please see Documentation/vm/pin_user_pages.rst. + * + * @page: pointer to page to be queried. + * @Return: True, if it is likely that the page has been "dma-pinned". + * False, if the page is definitely not dma-pinned. + */ +static inline bool page_maybe_dma_pinned(struct page *page) +{ + /* + * page_ref_count() is signed. If that refcount overflows, then + * page_ref_count() returns a negative value, and callers will avoid + * further incrementing the refcount. + * + * Here, for that overflow case, use the signed bit to count a little + * bit higher via unsigned math, and thus still get an accurate result. + */ + return ((unsigned int)page_ref_count(compound_head(page))) >=3D + GUP_PIN_COUNTING_BIAS; +} + #if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP) #define SECTION_IN_PAGE_FLAGS #endif --- a/mm/gup.c~mm-gup-track-foll_pin-pages +++ a/mm/gup.c @@ -44,6 +44,135 @@ static inline struct page *try_get_compo return head; } =20 +/* + * try_grab_compound_head() - attempt to elevate a page's refcount, by a + * flags-dependent amount. + * + * "grab" names in this file mean, "look at flags to decide whether to use + * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount. + * + * Either FOLL_PIN or FOLL_GET (or neither) must be set, but not both at t= he + * same time. (That's true throughout the get_user_pages*() and + * pin_user_pages*() APIs.) Cases: + * + * FOLL_GET: page's refcount will be incremented by 1. + * FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BI= AS. + * + * Return: head page (with refcount appropriately incremented) for success= , or + * NULL upon failure. If neither FOLL_GET nor FOLL_PIN was set, that's + * considered failure, and furthermore, a likely bug in the caller, so a w= arning + * is also emitted. + */ +static __maybe_unused struct page *try_grab_compound_head(struct page *pag= e, + int refs, + unsigned int flags) +{ + if (flags & FOLL_GET) + return try_get_compound_head(page, refs); + else if (flags & FOLL_PIN) { + refs *=3D GUP_PIN_COUNTING_BIAS; + return try_get_compound_head(page, refs); + } + + WARN_ON_ONCE(1); + return NULL; +} + +/** + * try_grab_page() - elevate a page's refcount by a flag-dependent amount + * + * This might not do anything at all, depending on the flags argument. + * + * "grab" names in this file mean, "look at flags to decide whether to use + * FOLL_PIN or FOLL_GET behavior, when incrementing the page's refcount. + * + * @page: pointer to page to be grabbed + * @flags: gup flags: these are the FOLL_* flag values. + * + * Either FOLL_PIN or FOLL_GET (or neither) may be set, but not both at th= e same + * time. Cases: + * + * FOLL_GET: page's refcount will be incremented by 1. + * FOLL_PIN: page's refcount will be incremented by GUP_PIN_COUNTING_BI= AS. + * + * Return: true for success, or if no action was required (if neither FOLL= _PIN + * nor FOLL_GET was set, nothing is done). False for failure: FOLL_GET or + * FOLL_PIN was set, but the page could not be grabbed. + */ +bool __must_check try_grab_page(struct page *page, unsigned int flags) +{ + WARN_ON_ONCE((flags & (FOLL_GET | FOLL_PIN)) =3D=3D (FOLL_GET | FOLL_PIN)= ); + + if (flags & FOLL_GET) + return try_get_page(page); + else if (flags & FOLL_PIN) { + page =3D compound_head(page); + + if (WARN_ON_ONCE(page_ref_count(page) <=3D 0)) + return false; + + page_ref_add(page, GUP_PIN_COUNTING_BIAS); + } + + return true; +} + +#ifdef CONFIG_DEV_PAGEMAP_OPS +static bool __unpin_devmap_managed_user_page(struct page *page) +{ + int count; + + if (!page_is_devmap_managed(page)) + return false; + + count =3D page_ref_sub_return(page, GUP_PIN_COUNTING_BIAS); + + /* + * devmap page refcounts are 1-based, rather than 0-based: if + * refcount is 1, then the page is free and the refcount is + * stable because nobody holds a reference on the page. + */ + if (count =3D=3D 1) + free_devmap_managed_page(page); + else if (!count) + __put_page(page); + + return true; +} +#else +static bool __unpin_devmap_managed_user_page(struct page *page) +{ + return false; +} +#endif /* CONFIG_DEV_PAGEMAP_OPS */ + +/** + * unpin_user_page() - release a dma-pinned page + * @page: pointer to page to be released + * + * Pages that were pinned via pin_user_pages*() must be released via either + * unpin_user_page(), or one of the unpin_user_pages*() routines. This is = so + * that such pages can be separately tracked and uniquely handled. In + * particular, interactions with RDMA and filesystems need special handlin= g. + */ +void unpin_user_page(struct page *page) +{ + page =3D compound_head(page); + + /* + * For devmap managed pages we need to catch refcount transition from + * GUP_PIN_COUNTING_BIAS to 1, when refcount reach one it means the + * page is free and we need to inform the device driver through + * callback. See include/linux/memremap.h and HMM for details. + */ + if (__unpin_devmap_managed_user_page(page)) + return; + + if (page_ref_sub_and_test(page, GUP_PIN_COUNTING_BIAS)) + __put_page(page); +} +EXPORT_SYMBOL(unpin_user_page); + /** * unpin_user_pages_dirty_lock() - release and optionally dirty gup-pinned= pages * @pages: array of pages to be maybe marked dirty, and definitely releas= ed. @@ -230,10 +359,11 @@ retry: } =20 page =3D vm_normal_page(vma, address, pte); - if (!page && pte_devmap(pte) && (flags & FOLL_GET)) { + if (!page && pte_devmap(pte) && (flags & (FOLL_GET | FOLL_PIN))) { /* - * Only return device mapping pages in the FOLL_GET case since - * they are only valid while holding the pgmap reference. + * Only return device mapping pages in the FOLL_GET or FOLL_PIN + * case since they are only valid while holding the pgmap + * reference. */ *pgmap =3D get_dev_pagemap(pte_pfn(pte), *pgmap); if (*pgmap) @@ -271,11 +401,10 @@ retry: goto retry; } =20 - if (flags & FOLL_GET) { - if (unlikely(!try_get_page(page))) { - page =3D ERR_PTR(-ENOMEM); - goto out; - } + /* try_grab_page() does nothing unless FOLL_GET or FOLL_PIN is set. */ + if (unlikely(!try_grab_page(page, flags))) { + page =3D ERR_PTR(-ENOMEM); + goto out; } if (flags & FOLL_TOUCH) { if ((flags & FOLL_WRITE) && @@ -537,7 +666,7 @@ static struct page *follow_page_mask(str /* make this handle hugepd */ page =3D follow_huge_addr(mm, address, flags & FOLL_WRITE); if (!IS_ERR(page)) { - BUG_ON(flags & FOLL_GET); + WARN_ON_ONCE(flags & (FOLL_GET | FOLL_PIN)); return page; } =20 @@ -1675,6 +1804,15 @@ long get_user_pages_remote(struct task_s { return 0; } + +static 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) +{ + return 0; +} #endif /* !CONFIG_MMU */ =20 /* @@ -1814,7 +1952,24 @@ EXPORT_SYMBOL(get_user_pages_unlocked); * This code is based heavily on the PowerPC implementation by Nick Piggin. */ #ifdef CONFIG_HAVE_FAST_GUP + +static void put_compound_head(struct page *page, int refs, unsigned int fl= ags) +{ + if (flags & FOLL_PIN) + refs *=3D GUP_PIN_COUNTING_BIAS; + + VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); + /* + * Calling put_page() for each ref is unnecessarily slow. Only the last + * ref needs a put_page(). + */ + if (refs > 1) + page_ref_sub(page, refs - 1); + put_page(page); +} + #ifdef CONFIG_GUP_GET_PTE_LOW_HIGH + /* * WARNING: only to be used in the get_user_pages_fast() implementation. * @@ -1877,7 +2032,10 @@ static void __maybe_unused undo_dev_page struct page *page =3D pages[--(*nr)]; =20 ClearPageReferenced(page); - put_page(page); + if (flags & FOLL_PIN) + unpin_user_page(page); + else + put_page(page); } } =20 @@ -1919,12 +2077,12 @@ static int gup_pte_range(pmd_t pmd, unsi VM_BUG_ON(!pfn_valid(pte_pfn(pte))); page =3D pte_page(pte); =20 - head =3D try_get_compound_head(page, 1); + head =3D try_grab_compound_head(page, 1, flags); if (!head) goto pte_unmap; =20 if (unlikely(pte_val(pte) !=3D pte_val(*ptep))) { - put_page(head); + put_compound_head(head, 1, flags); goto pte_unmap; } =20 @@ -1980,7 +2138,10 @@ static int __gup_device_huge(unsigned lo } SetPageReferenced(page); pages[*nr] =3D page; - get_page(page); + if (unlikely(!try_grab_page(page, flags))) { + undo_dev_pagemap(nr, nr_start, flags, pages); + return 0; + } (*nr)++; pfn++; } while (addr +=3D PAGE_SIZE, addr !=3D end); @@ -2054,18 +2215,6 @@ static int record_subpages(struct page * return nr; } =20 -static void put_compound_head(struct page *page, int refs, unsigned int fl= ags) -{ - VM_BUG_ON_PAGE(page_ref_count(page) < refs, page); - /* - * Calling put_page() for each ref is unnecessarily slow. Only the last - * ref needs a put_page(). - */ - if (refs > 1) - page_ref_sub(page, refs - 1); - put_page(page); -} - #ifdef CONFIG_ARCH_HAS_HUGEPD static unsigned long hugepte_addr_end(unsigned long addr, unsigned long en= d, unsigned long sz) @@ -2099,7 +2248,7 @@ static int gup_hugepte(pte_t *ptep, unsi page =3D head + ((addr & (sz-1)) >> PAGE_SHIFT); refs =3D record_subpages(page, addr, end, pages + *nr); =20 - head =3D try_get_compound_head(head, refs); + head =3D try_grab_compound_head(head, refs, flags); if (!head) return 0; =20 @@ -2159,7 +2308,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_ page =3D pmd_page(orig) + ((addr & ~PMD_MASK) >> PAGE_SHIFT); refs =3D record_subpages(page, addr, end, pages + *nr); =20 - head =3D try_get_compound_head(pmd_page(orig), refs); + head =3D try_grab_compound_head(pmd_page(orig), refs, flags); if (!head) return 0; =20 @@ -2193,7 +2342,7 @@ static int gup_huge_pud(pud_t orig, pud_ page =3D pud_page(orig) + ((addr & ~PUD_MASK) >> PAGE_SHIFT); refs =3D record_subpages(page, addr, end, pages + *nr); =20 - head =3D try_get_compound_head(pud_page(orig), refs); + head =3D try_grab_compound_head(pud_page(orig), refs, flags); if (!head) return 0; =20 @@ -2222,7 +2371,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_ page =3D pgd_page(orig) + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT); refs =3D record_subpages(page, addr, end, pages + *nr); =20 - head =3D try_get_compound_head(pgd_page(orig), refs); + head =3D try_grab_compound_head(pgd_page(orig), refs, flags); if (!head) return 0; =20 @@ -2505,11 +2654,11 @@ static int internal_get_user_pages_fast( =20 /** * 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. + * @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 @@ -2543,9 +2692,18 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast); /** * pin_user_pages_fast() - pin user pages in memory without taking locks * - * For now, this is a placeholder function, until various call sites are - * converted to use the correct get_user_pages*() or pin_user_pages*() API= . So, - * this is identical to get_user_pages_fast(). + * @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. + * + * 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, beca= use + * the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via unpin_user_page(). P= lease + * see Documentation/vm/pin_user_pages.rst for further details. * * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rs= t. It * is NOT intended for Case 2 (RDMA: long-term pins). @@ -2553,21 +2711,39 @@ EXPORT_SYMBOL_GPL(get_user_pages_fast); int pin_user_pages_fast(unsigned long start, int nr_pages, unsigned int gup_flags, struct page **pages) { - /* - * This is a placeholder, until the pin functionality is activated. - * Until then, just behave like the corresponding get_user_pages*() - * routine. - */ - return get_user_pages_fast(start, nr_pages, gup_flags, pages); + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |=3D FOLL_PIN; + return internal_get_user_pages_fast(start, nr_pages, gup_flags, pages); } EXPORT_SYMBOL_GPL(pin_user_pages_fast); =20 /** * pin_user_pages_remote() - pin pages of a remote process (task !=3D curr= ent) * - * For now, this is a placeholder function, until various call sites are - * converted to use the correct get_user_pages*() or pin_user_pages*() API= . So, - * this is identical to get_user_pages_remote(). + * @tsk: the task_struct to use for page fault accounting, or + * NULL if faults are not to be recorded. + * @mm: mm_struct of target mm + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @gup_flags: flags modifying lookup behaviour + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. Or NULL, if caller + * only intends to ensure the pages are faulted in. + * @vmas: array of pointers to vmas corresponding to each page. + * Or NULL if the caller does not require them. + * @locked: pointer to lock flag indicating whether lock is held and + * subsequently whether VM_FAULT_RETRY functionality can be + * utilised. Lock must initially be held. + * + * 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, be= cause + * the arguments here are identical. + * + * FOLL_PIN means that the pages must be released via unpin_user_page(). P= lease + * see Documentation/vm/pin_user_pages.rst for details. * * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rs= t. It * is NOT intended for Case 2 (RDMA: long-term pins). @@ -2577,22 +2753,33 @@ long pin_user_pages_remote(struct task_s unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas, int *locked) { - /* - * This is a placeholder, until the pin functionality is activated. - * Until then, just behave like the corresponding get_user_pages*() - * routine. - */ - return get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags, pages, - vmas, locked); + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |=3D FOLL_PIN; + return __get_user_pages_remote(tsk, mm, start, nr_pages, gup_flags, + pages, vmas, locked); } EXPORT_SYMBOL(pin_user_pages_remote); =20 /** * pin_user_pages() - pin user pages in memory for use by other devices * - * For now, this is a placeholder function, until various call sites are - * converted to use the correct get_user_pages*() or pin_user_pages*() API= . So, - * this is identical to get_user_pages(). + * @start: starting user address + * @nr_pages: number of pages from start to pin + * @gup_flags: flags modifying lookup behaviour + * @pages: array that receives pointers to the pages pinned. + * Should be at least nr_pages long. Or NULL, if caller + * only intends to ensure the pages are faulted in. + * @vmas: array of pointers to vmas corresponding to each page. + * Or NULL if the caller does not require them. + * + * 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 unpin_user_page(). P= lease + * see Documentation/vm/pin_user_pages.rst for details. * * This is intended for Case 1 (DIO) in Documentation/vm/pin_user_pages.rs= t. It * is NOT intended for Case 2 (RDMA: long-term pins). @@ -2601,11 +2788,12 @@ long pin_user_pages(unsigned long start, unsigned int gup_flags, struct page **pages, struct vm_area_struct **vmas) { - /* - * This is a placeholder, until the pin functionality is activated. - * Until then, just behave like the corresponding get_user_pages*() - * routine. - */ - return get_user_pages(start, nr_pages, gup_flags, pages, vmas); + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE(gup_flags & FOLL_GET)) + return -EINVAL; + + gup_flags |=3D FOLL_PIN; + return __gup_longterm_locked(current, current->mm, start, nr_pages, + pages, vmas, gup_flags); } EXPORT_SYMBOL(pin_user_pages); --- a/mm/huge_memory.c~mm-gup-track-foll_pin-pages +++ a/mm/huge_memory.c @@ -958,6 +958,11 @@ struct page *follow_devmap_pmd(struct vm */ WARN_ONCE(flags & FOLL_COW, "mm: In follow_devmap_pmd with FOLL_COW set"); =20 + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) =3D=3D + (FOLL_PIN | FOLL_GET))) + return NULL; + if (flags & FOLL_WRITE && !pmd_write(*pmd)) return NULL; =20 @@ -973,7 +978,7 @@ struct page *follow_devmap_pmd(struct vm * device mapped pages can only be returned if the * caller will manage the page reference count. */ - if (!(flags & FOLL_GET)) + if (!(flags & (FOLL_GET | FOLL_PIN))) return ERR_PTR(-EEXIST); =20 pfn +=3D (addr & ~PMD_MASK) >> PAGE_SHIFT; @@ -981,7 +986,8 @@ struct page *follow_devmap_pmd(struct vm if (!*pgmap) return ERR_PTR(-EFAULT); page =3D pfn_to_page(pfn); - get_page(page); + if (!try_grab_page(page, flags)) + page =3D ERR_PTR(-ENOMEM); =20 return page; } @@ -1101,6 +1107,11 @@ struct page *follow_devmap_pud(struct vm if (flags & FOLL_WRITE && !pud_write(*pud)) return NULL; =20 + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) =3D=3D + (FOLL_PIN | FOLL_GET))) + return NULL; + if (pud_present(*pud) && pud_devmap(*pud)) /* pass */; else @@ -1112,8 +1123,10 @@ struct page *follow_devmap_pud(struct vm /* * device mapped pages can only be returned if the * caller will manage the page reference count. + * + * At least one of FOLL_GET | FOLL_PIN must be set, so assert that here: */ - if (!(flags & FOLL_GET)) + if (!(flags & (FOLL_GET | FOLL_PIN))) return ERR_PTR(-EEXIST); =20 pfn +=3D (addr & ~PUD_MASK) >> PAGE_SHIFT; @@ -1121,7 +1134,8 @@ struct page *follow_devmap_pud(struct vm if (!*pgmap) return ERR_PTR(-EFAULT); page =3D pfn_to_page(pfn); - get_page(page); + if (!try_grab_page(page, flags)) + page =3D ERR_PTR(-ENOMEM); =20 return page; } @@ -1497,8 +1511,13 @@ struct page *follow_trans_huge_pmd(struc =20 page =3D pmd_page(*pmd); VM_BUG_ON_PAGE(!PageHead(page) && !is_zone_device_page(page), page); + + if (!try_grab_page(page, flags)) + return ERR_PTR(-ENOMEM); + if (flags & FOLL_TOUCH) touch_pmd(vma, addr, pmd, flags); + if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) { /* * We don't mlock() pte-mapped THPs. This way we can avoid @@ -1535,8 +1554,6 @@ struct page *follow_trans_huge_pmd(struc skip_mlock: page +=3D (addr & ~HPAGE_PMD_MASK) >> PAGE_SHIFT; VM_BUG_ON_PAGE(!PageCompound(page) && !is_zone_device_page(page), page); - if (flags & FOLL_GET) - get_page(page); =20 out: return page; --- a/mm/hugetlb.c~mm-gup-track-foll_pin-pages +++ a/mm/hugetlb.c @@ -4376,19 +4376,6 @@ long follow_hugetlb_page(struct mm_struc page =3D pte_page(huge_ptep_get(pte)); =20 /* - * Instead of doing 'try_get_page()' below in the same_page - * loop, just check the count once here. - */ - if (unlikely(page_count(page) <=3D 0)) { - if (pages) { - spin_unlock(ptl); - remainder =3D 0; - err =3D -ENOMEM; - break; - } - } - - /* * If subpage information not requested, update counters * and skip the same_page loop below. */ @@ -4405,7 +4392,22 @@ long follow_hugetlb_page(struct mm_struc same_page: if (pages) { pages[i] =3D mem_map_offset(page, pfn_offset); - get_page(pages[i]); + /* + * try_grab_page() should always succeed here, because: + * a) we hold the ptl lock, and b) we've just checked + * that the huge page is present in the page tables. If + * the huge page is present, then the tail pages must + * also be present. The ptl prevents the head page and + * tail pages from being rearranged in any way. So this + * page must be available at this point, unless the page + * refcount overflowed: + */ + if (WARN_ON_ONCE(!try_grab_page(pages[i], flags))) { + spin_unlock(ptl); + remainder =3D 0; + err =3D -ENOMEM; + break; + } } =20 if (vmas) @@ -4965,6 +4967,12 @@ follow_huge_pmd(struct mm_struct *mm, un struct page *page =3D NULL; spinlock_t *ptl; pte_t pte; + + /* FOLL_GET and FOLL_PIN are mutually exclusive. */ + if (WARN_ON_ONCE((flags & (FOLL_PIN | FOLL_GET)) =3D=3D + (FOLL_PIN | FOLL_GET))) + return NULL; + retry: ptl =3D pmd_lockptr(mm, pmd); spin_lock(ptl); @@ -4977,8 +4985,18 @@ retry: pte =3D huge_ptep_get((pte_t *)pmd); if (pte_present(pte)) { page =3D pmd_page(*pmd) + ((address & ~PMD_MASK) >> PAGE_SHIFT); - if (flags & FOLL_GET) - get_page(page); + /* + * try_grab_page() should always succeed here, because: a) we + * hold the pmd (ptl) lock, and b) we've just checked that the + * huge pmd (head) page is present in the page tables. The ptl + * prevents the head page and tail pages from being rearranged + * in any way. So this page must be available at this point, + * unless the page refcount overflowed: + */ + if (WARN_ON_ONCE(!try_grab_page(page, flags))) { + page =3D NULL; + goto out; + } } else { if (is_hugetlb_entry_migration(pte)) { spin_unlock(ptl); @@ -4999,7 +5017,7 @@ struct page * __weak follow_huge_pud(struct mm_struct *mm, unsigned long address, pud_t *pud, int flags) { - if (flags & FOLL_GET) + if (flags & (FOLL_GET | FOLL_PIN)) return NULL; =20 return pte_page(*(pte_t *)pud) + ((address & ~PUD_MASK) >> PAGE_SHIFT); @@ -5008,7 +5026,7 @@ follow_huge_pud(struct mm_struct *mm, un struct page * __weak follow_huge_pgd(struct mm_struct *mm, unsigned long address, pgd_t *pgd, i= nt flags) { - if (flags & FOLL_GET) + if (flags & (FOLL_GET | FOLL_PIN)) return NULL; =20 return pte_page(*(pte_t *)pgd) + ((address & ~PGDIR_MASK) >> PAGE_SHIFT); _