From patchwork Tue May 19 00:21:22 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Hubbard X-Patchwork-Id: 11556555 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 BE0E5138A for ; Tue, 19 May 2020 00:21:42 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 9C11520715 for ; Tue, 19 May 2020 00:21:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="roJzug6F" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9C11520715 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=dri-devel-bounces@lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 585366E4C1; Tue, 19 May 2020 00:21:36 +0000 (UTC) X-Original-To: dri-devel@lists.freedesktop.org Delivered-To: dri-devel@lists.freedesktop.org Received: from hqnvemgate26.nvidia.com (hqnvemgate26.nvidia.com [216.228.121.65]) by gabe.freedesktop.org (Postfix) with ESMTPS id E4EDB6E4C5; Tue, 19 May 2020 00:21:30 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Mon, 18 May 2020 17:21:18 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Mon, 18 May 2020 17:21:30 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Mon, 18 May 2020 17:21:30 -0700 Received: from HQMAIL107.nvidia.com (172.20.187.13) by HQMAIL101.nvidia.com (172.20.187.10) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Tue, 19 May 2020 00:21:27 +0000 Received: from rnnvemgw01.nvidia.com (10.128.109.123) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3 via Frontend Transport; Tue, 19 May 2020 00:21:27 +0000 Received: from sandstorm.nvidia.com (Not Verified[10.2.55.90]) by rnnvemgw01.nvidia.com with Trustwave SEG (v7, 5, 8, 10121) id ; Mon, 18 May 2020 17:21:27 -0700 From: John Hubbard To: Andrew Morton Subject: [PATCH 2/4] mm/gup: refactor and de-duplicate gup_fast() code Date: Mon, 18 May 2020 17:21:22 -0700 Message-ID: <20200519002124.2025955-3-jhubbard@nvidia.com> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200519002124.2025955-1-jhubbard@nvidia.com> References: <20200519002124.2025955-1-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=1589847678; bh=eKEEE/Y/vrnjqqbzDXfpG1tDQCyxBc2uk5PwdO7UHPs=; 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=roJzug6FRflfc5QOO84Nkmt/6yLm+3EdG5LWcwiimEiXJEmmGzLwiOsKBkg64BP1R yInCML2+VZTK3BiC3zBszmooskpy/aCsUaSDWsyDyd0g9TgCxJWBcEALOLx2b3IbPW zHq6A6OFlGYF2J/822ehCPooN1GK9t489gBEm/opQfMuUILvA4D05VVg1uvhWaeiub KGcDCDjk+KZZ6yH1Ahq4zouqWldX5K6E3aV2UnFVQKQctZf8e+fqGP9DU+SCF71ATe e5eaCHWXKtp3eVsNY+MaBe5hWwlSnTxBRrLO70c96RT1jp3pQsYa8wDK/fa3ij6kxa 96mAjLKM6Jizg== X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Matthew Wilcox , dri-devel@lists.freedesktop.org, Tvrtko Ursulin , David Airlie , John Hubbard , intel-gfx@lists.freedesktop.org, LKML , Chris Wilson , linux-mm@kvack.org, Souptick Joarder , Rodrigo Vivi , Matthew Auld Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" There were two nearly identical sets of code for gup_fast() style of walking the page tables with interrupts disabled. This has lead to the usual maintenance problems that arise from having duplicated code. There is already a core internal routine in gup.c for gup_fast(), so just enhance it very slightly: allow skipping the fall-back to "slow" (regular) get_user_pages(), via the new FOLL_FAST_ONLY flag. Then, just call internal_get_user_pages_fast() from __get_user_pages_fast(), and adjust the API to match pre-existing API behavior. There is a change in behavior from this refactoring: the nested form of interrupt disabling is used in all gup_fast() variants now. That's because there is only one place that interrupt disabling for page walking is done, and so the safer form is required. This should, if anything, eliminate possible (rare) bugs, because the non-nested form of enabling interrupts was fragile at best. Signed-off-by: John Hubbard --- include/linux/mm.h | 1 + mm/gup.c | 60 ++++++++++++++++++++++------------------------ 2 files changed, 29 insertions(+), 32 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index a5594ac9ebe3..84b601cab699 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -2782,6 +2782,7 @@ struct page *follow_page(struct vm_area_struct *vma, unsigned long address, #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 unpin_user_page */ +#define FOLL_FAST_ONLY 0x80000 /* gup_fast: prevent fall-back to slow gup */ /* * FOLL_PIN and FOLL_LONGTERM may be used in various combinations with each diff --git a/mm/gup.c b/mm/gup.c index 4502846d57f9..bb3e2c4288c3 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2694,6 +2694,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, struct page **pages) { unsigned long addr, len, end; + unsigned long flags; int nr_pinned = 0, ret = 0; if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM | @@ -2710,15 +2711,26 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, 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)) { - local_irq_disable(); + local_irq_save(flags); gup_pgd_range(addr, end, gup_flags, pages, &nr_pinned); - local_irq_enable(); + local_irq_restore(flags); ret = nr_pinned; } - if (nr_pinned < nr_pages) { + 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; @@ -2750,45 +2762,29 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages, int __get_user_pages_fast(unsigned long start, int nr_pages, int write, struct page **pages) { - unsigned long len, end; - unsigned long flags; - int nr_pinned = 0; + int nr_pinned; /* * Internally (within mm/gup.c), gup fast variants must set FOLL_GET, * because gup fast is always a "pin with a +1 page refcount" request. + * + * FOLL_FAST_ONLY is required in order to match the API description of + * this routine: no fall back to regular ("slow") GUP. */ - unsigned int gup_flags = FOLL_GET; + unsigned int gup_flags = FOLL_GET | FOLL_FAST_ONLY; if (write) gup_flags |= FOLL_WRITE; - start = untagged_addr(start) & PAGE_MASK; - len = (unsigned long) nr_pages << PAGE_SHIFT; - end = start + len; - - if (end <= start) - return 0; - if (unlikely(!access_ok((void __user *)start, len))) - return 0; - + nr_pinned = internal_get_user_pages_fast(start, nr_pages, gup_flags, + pages); /* - * Disable interrupts. We use the nested form as we can already have - * interrupts disabled by get_futex_key. - * - * 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. + * As specified in the API description above, this routine is not + * allowed to return negative values. However, the common core + * routine internal_get_user_pages_fast() *can* return -errno. + * Therefore, correct for that here: */ - - if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) && - gup_fast_permitted(start, end)) { - local_irq_save(flags); - gup_pgd_range(start, end, gup_flags, pages, &nr_pinned); - local_irq_restore(flags); - } + if (nr_pinned < 0) + nr_pinned = 0; return nr_pinned; }