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 Received: from lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 2E8ECC47079 for ; Wed, 3 Jan 2024 09:20:29 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=JZCj12hf; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=JZCj12hf; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4T4khq4bL7z3btQ for ; Wed, 3 Jan 2024 20:20:27 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=JZCj12hf; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=JZCj12hf; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=redhat.com (client-ip=170.10.129.124; helo=us-smtp-delivery-124.mimecast.com; envelope-from=peterx@redhat.com; receiver=lists.ozlabs.org) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4T4kbj75WDz3cTS for ; Wed, 3 Jan 2024 20:16:01 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704273359; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=G2mMJAnaoVdNju5RvSwq+KPjZVLCTkTT7F8NTqIl1do=; b=JZCj12hfHLUzaG/h35VSyuXf/8H0D9+mUHyX+sK7DaCt8Sca5HEnnx5idjPinzPae7kp4J /RPUFe0Tgh+JiBwpYrG0BZYMHkU/EUx3rg0QPK0LRSdIVergeZKY17RR1Cj5VWjcRK6/L6 aoJ4/233uc5knkiRsfolx2TPrhurVi4= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704273359; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=G2mMJAnaoVdNju5RvSwq+KPjZVLCTkTT7F8NTqIl1do=; b=JZCj12hfHLUzaG/h35VSyuXf/8H0D9+mUHyX+sK7DaCt8Sca5HEnnx5idjPinzPae7kp4J /RPUFe0Tgh+JiBwpYrG0BZYMHkU/EUx3rg0QPK0LRSdIVergeZKY17RR1Cj5VWjcRK6/L6 aoJ4/233uc5knkiRsfolx2TPrhurVi4= Received: from mimecast-mx02.redhat.com (mx-ext.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-597-sJHnyUgTOIGCIKVC1MWAaQ-1; Wed, 03 Jan 2024 04:15:53 -0500 X-MC-Unique: sJHnyUgTOIGCIKVC1MWAaQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 731831C0512D; Wed, 3 Jan 2024 09:15:52 +0000 (UTC) Received: from x1n.redhat.com (unknown [10.72.116.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id DBCD9492BE6; Wed, 3 Jan 2024 09:15:41 +0000 (UTC) From: peterx@redhat.com To: linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 06/13] mm/gup: Drop folio_fast_pin_allowed() in hugepd processing Date: Wed, 3 Jan 2024 17:14:16 +0800 Message-ID: <20240103091423.400294-7-peterx@redhat.com> In-Reply-To: <20240103091423.400294-1-peterx@redhat.com> References: <20240103091423.400294-1-peterx@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.10 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: James Houghton , David Hildenbrand , Yang Shi , peterx@redhat.com, Andrew Jones , Matthew Wilcox , linux-riscv@lists.infradead.org, Andrea Arcangeli , Christoph Hellwig , "Aneesh Kumar K . V" , Vlastimil Babka , Jason Gunthorpe , Axel Rasmussen , Rik van Riel , John Hubbard , "Kirill A . Shutemov" , linux-arm-kernel@lists.infradead.org, Lorenzo Stoakes , Muchun Song , Andrew Morton , linuxppc-dev@lists.ozlabs.org, Mike Rapoport , Mike Kravetz Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" From: Peter Xu Hugepd format for GUP is only used in PowerPC with hugetlbfs. There are some kernel usage of hugepd (can refer to hugepd_populate_kernel() for PPC_8XX), however those pages are not candidates for GUP. Commit a6e79df92e4a ("mm/gup: disallow FOLL_LONGTERM GUP-fast writing to file-backed mappings") added a check to fail gup-fast if there's potential risk of violating GUP over writeback file systems. That should never apply to hugepd. Considering that hugepd is an old format (and even software-only), there's no plan to extend hugepd into other file typed memories that is prone to the same issue. Drop that check, not only because it'll never be true for hugepd per any known plan, but also it paves way for reusing the function outside fast-gup. To make sure we'll still remember this issue just in case hugepd will be extended to support non-hugetlbfs memories, add a rich comment above gup_huge_pd(), explaining the issue with proper references. Cc: Christoph Hellwig Cc: Lorenzo Stoakes Cc: Michael Ellerman Cc: linuxppc-dev@lists.ozlabs.org Signed-off-by: Peter Xu --- mm/gup.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/mm/gup.c b/mm/gup.c index eebae70d2465..fa93e14b7fca 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -2820,11 +2820,6 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, return 0; } - if (!folio_fast_pin_allowed(folio, flags)) { - gup_put_folio(folio, refs, flags); - return 0; - } - if (!pte_write(pte) && gup_must_unshare(NULL, flags, &folio->page)) { gup_put_folio(folio, refs, flags); return 0; @@ -2835,6 +2830,14 @@ static int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, return 1; } +/* + * NOTE: currently GUP for a hugepd is only possible on hugetlbfs file + * systems on Power, which does not have issue with folio writeback against + * GUP updates. When hugepd will be extended to support non-hugetlbfs or + * even anonymous memory, we need to do extra check as what we do with most + * of the other folios. See writable_file_mapping_allowed() and + * folio_fast_pin_allowed() for more information. + */ static int gup_huge_pd(hugepd_t hugepd, unsigned long addr, unsigned int pdshift, unsigned long end, unsigned int flags, struct page **pages, int *nr) -- 2.41.0