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=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 B36A0C4741F for ; Fri, 30 Oct 2020 16:29:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5AF9620A8B for ; Fri, 30 Oct 2020 16:29:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727021AbgJ3Q3O (ORCPT ); Fri, 30 Oct 2020 12:29:14 -0400 Received: from mx2.suse.de ([195.135.220.15]:41716 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725844AbgJ3Q3N (ORCPT ); Fri, 30 Oct 2020 12:29:13 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 2C09EACF5; Fri, 30 Oct 2020 16:29:12 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id A1F6B1E12F3; Fri, 30 Oct 2020 17:29:11 +0100 (CET) Date: Fri, 30 Oct 2020 17:29:11 +0100 From: Jan Kara To: Jason Gunthorpe Cc: linux-kernel@vger.kernel.org, Peter Xu , Linus Torvalds , 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: Re: [PATCH v2 1/2] mm: reorganize internal_get_user_pages_fast() Message-ID: <20201030162911.GG19757@quack2.suse.cz> References: <0-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> <1-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1-v2-dfe9ecdb6c74+2066-gup_fork_jgg@nvidia.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 30-10-20 11:46:20, Jason Gunthorpe wrote: > 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. > > Signed-off-by: Jason Gunthorpe Looks good to me. You can add: Reviewed-by: Jan Kara Honza > --- > mm/gup.c | 99 ++++++++++++++++++++++++++++++-------------------------- > 1 file changed, 54 insertions(+), 45 deletions(-) > > diff --git a/mm/gup.c b/mm/gup.c > index 102877ed77a4b4..150cc962c99201 100644 > --- a/mm/gup.c > +++ b/mm/gup.c > @@ -2671,13 +2671,43 @@ 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 | > @@ -2691,54 +2721,33 @@ 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; > - } > + nr_pinned = lockless_pages_from_mm(start, end, gup_flags, pages); > + if (nr_pinned == nr_pages || gup_flags & FOLL_FAST_ONLY) > + return 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; > - > - 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 > -- > 2.28.0 > -- Jan Kara SUSE Labs, CR