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Tue, 10 Nov 2020 23:44:11 +0000 From: Jason Gunthorpe To: , Peter Xu , Linus Torvalds CC: "Ahmed S. Darwish" , Andrea Arcangeli , Andrew Morton , Christoph Hellwig , Hugh Dickins , Jan Kara , Jann Horn , John Hubbard , Kirill Shutemov , Kirill Tkhai , Linux-MM , Michal Hocko , Oleg Nesterov Subject: [PATCH v4 1/2] mm: reorganize internal_get_user_pages_fast() Date: Tue, 10 Nov 2020 19:44:08 -0400 Message-ID: <1-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com> In-Reply-To: <0-v4-908497cf359a+4782-gup_fork_jgg@nvidia.com> References: X-ClientProxiedBy: BL1PR13CA0142.namprd13.prod.outlook.com (2603:10b6:208:2bb::27) To DM6PR12MB3834.namprd12.prod.outlook.com (2603:10b6:5:14a::12) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from mlx.ziepe.ca (156.34.48.30) by BL1PR13CA0142.namprd13.prod.outlook.com (2603:10b6:208:2bb::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3564.21 via Frontend Transport; Tue, 10 Nov 2020 23:44:10 +0000 Received: from jgg by mlx with local (Exim 4.94) (envelope-from ) id 1kcdJ3-0036MI-DK; Tue, 10 Nov 2020 19:44:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1605051856; bh=8vfCpzh0Dz7yx0tdFAZh1nokwVWioFMWryE1oM5j7GE=; h=ARC-Seal:ARC-Message-Signature:ARC-Authentication-Results:From:To: CC:Subject:Date:Message-ID:In-Reply-To:References: Content-Transfer-Encoding:Content-Type:X-ClientProxiedBy: MIME-Version:X-MS-Exchange-MessageSentRepresentingType; b=gogLLacECClb1Mcflu5u1ZebePQOt/CXsRt0DmP+DiA1jppVJPBBQ3QeFjDhTdc7k xNSIC6KRsMiQdg1zpioH1v/NdRkvdQXsp4y2/SrFnYHbE7zacg3Uo7oeHImfaKcMCj ia09OACh10jCVZte73QWafP4mlpgRffljWvfCIDEA8czNsl6O6PpoSonFjn/PyLvVT y1IsheqqzfPUfyVSgq5urQ+qJK0q/D3Gq67jwCjY7k7VGoaF2iTFuBK9H5zXEVOmIv NTLHWSQ6RvU0Njd7e43tsYdwrynF4YezMf+S6LMG9sR/ngeoZtaF+37C7nCSvyOcQg Te7GDto/ocSWg== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: The next patch in this series makes the lockless flow a little more complex, so move the entire block into a new function and remove a level of indention. Tidy a bit of cruft: - addr is always the same as start, so use start - Use the modern check_add_overflow() for computing end = start + len - nr_pinned/pages << PAGE_SHIFT needs the LHS to be unsigned long to avoid shift overflow, make the variables unsigned long to avoid coding casts in both places. nr_pinned was missing its cast - The handling of ret and nr_pinned can be streamlined a bit No functional change. Reviewed-by: Jan Kara Reviewed-by: John Hubbard Reviewed-by: Peter Xu Signed-off-by: Jason Gunthorpe --- mm/gup.c | 99 ++++++++++++++++++++++++++++++-------------------------- 1 file changed, 54 insertions(+), 45 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index 98eb8e6d2609c3..c7e24301860abb 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2677,13 +2677,43 @@ static int __gup_longterm_unlocked(unsigned long start, int nr_pages, return ret; } -static int internal_get_user_pages_fast(unsigned long start, int nr_pages, +static unsigned long lockless_pages_from_mm(unsigned long start, + unsigned long end, + unsigned int gup_flags, + struct page **pages) +{ + unsigned long flags; + int nr_pinned = 0; + + if (!IS_ENABLED(CONFIG_HAVE_FAST_GUP) || + !gup_fast_permitted(start, end)) + return 0; + + /* + * Disable interrupts. The nested form is used, in order to allow full, + * general purpose use of this routine. + * + * With interrupts disabled, we block page table pages from being freed + * from under us. See struct mmu_table_batch comments in + * include/asm-generic/tlb.h for more details. + * + * We do not adopt an rcu_read_lock() here as we also want to block IPIs + * that come from THPs splitting. + */ + local_irq_save(flags); + gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); + local_irq_restore(flags); + return nr_pinned; +} + +static int internal_get_user_pages_fast(unsigned long start, + unsigned long nr_pages, unsigned int gup_flags, struct page **pages) { - unsigned long addr, len, end; - unsigned long flags; - int nr_pinned = 0, ret = 0; + unsigned long len, end; + unsigned long nr_pinned; + int ret; if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | FOLL_FORCE | FOLL_PIN | FOLL_GET | @@ -2697,54 +2727,33 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, might_lock_read(¤t->mm->mmap_lock); start = untagged_addr(start) & PAGE_MASK; - addr = start; - len = (unsigned long) nr_pages << PAGE_SHIFT; - end = start + len; - - if (end <= start) + len = nr_pages << PAGE_SHIFT; + if (check_add_overflow(start, len, &end)) return 0; if (unlikely(!access_ok((void __user *)start, len))) return -EFAULT; - /* - * Disable interrupts. The nested form is used, in order to allow - * full, general purpose use of this routine. - * - * With interrupts disabled, we block page table pages from being - * freed from under us. See struct mmu_table_batch comments in - * include/asm-generic/tlb.h for more details. - * - * We do not adopt an rcu_read_lock(.) here as we also want to - * block IPIs that come from THPs splitting. - */ - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && gup_fast_permitted(start, end)) { - unsigned long fast_flags = gup_flags; - - local_irq_save(flags); - gup_pgd_range(addr, end, fast_flags, pages, &nr_pinned); - local_irq_restore(flags); - ret = nr_pinned; - } - - if (nr_pinned < nr_pages && !(gup_flags & FOLL_FAST_ONLY)) { - /* Try to get the remaining pages with get_user_pages */ - start += nr_pinned << PAGE_SHIFT; - pages += nr_pinned; + nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages); + if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY) + return nr_pinned; - ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, - gup_flags, pages); - - /* Have to be a bit careful with return values */ - if (nr_pinned > 0) { - if (ret < 0) - ret = nr_pinned; - else - ret += nr_pinned; - } + /* Slow path: try to get the remaining pages with get_user_pages */ + start += nr_pinned << PAGE_SHIFT; + pages += nr_pinned; + ret = __gup_longterm_unlocked(start, nr_pages - nr_pinned, gup_flags, + pages); + if (ret < 0) { + /* + * The caller has to unpin the pages we already pinned so + * returning -errno is not an option + */ + if (nr_pinned) + return nr_pinned; + return ret; } - - return ret; + return ret + nr_pinned; } + /** * get_user_pages_fast_only() - pin user pages in memory * @start: starting user address