From patchwork Mon Nov 7 16:17:29 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Hildenbrand X-Patchwork-Id: 13034787 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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id DB6D0C4332F for ; Mon, 7 Nov 2022 16:18:58 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 59A0A10E46C; Mon, 7 Nov 2022 16:18:57 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by gabe.freedesktop.org (Postfix) with ESMTPS id 8E3B710E46D for ; Mon, 7 Nov 2022 16:18:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1667837920; 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=bBnIIqhyhD6iyBujMvwC62HNjvRYMc/Z3DOfUddgdGg=; b=OA8GF7a3N147aCsY+7FG/wvWm9eElT7WAGBMZsogUhwXZyvKxNHwxgvIsqfVuqgkp81XS6 awB8QL2wnm26pgoX4N/OrWgGhgRtJ+YB2eckXj2K5fOUj1KTyPGaOY9LLClRbhYSfq5zZC Mc89S8ucJeOZtyKXKkCogmW3iGffoQY= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-463-grZU38baPf-7EYRvd2zYkw-1; Mon, 07 Nov 2022 11:18:37 -0500 X-MC-Unique: grZU38baPf-7EYRvd2zYkw-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 776FE3C0E462; Mon, 7 Nov 2022 16:18:34 +0000 (UTC) Received: from t480s.redhat.com (unknown [10.39.195.106]) by smtp.corp.redhat.com (Postfix) with ESMTP id CF99B4B3FC6; Mon, 7 Nov 2022 16:18:28 +0000 (UTC) From: David Hildenbrand To: linux-kernel@vger.kernel.org Subject: [PATCH RFC 08/19] mm: extend FAULT_FLAG_UNSHARE support to anything in a COW mapping Date: Mon, 7 Nov 2022 17:17:29 +0100 Message-Id: <20221107161740.144456-9-david@redhat.com> In-Reply-To: <20221107161740.144456-1-david@redhat.com> References: <20221107161740.144456-1-david@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 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: David Hildenbrand , dri-devel@lists.freedesktop.org, linux-mm@kvack.org, Nadav Amit , linux-kselftest@vger.kernel.org, Andrea Arcangeli , linux-samsung-soc@vger.kernel.org, linux-rdma@vger.kernel.org, Hugh Dickins , Matthew Wilcox , Jason Gunthorpe , linux-arm-kernel@lists.infradead.org, linux-media@vger.kernel.org, Arnd Bergmann , John Hubbard , etnaviv@lists.freedesktop.org, Peter Xu , Muchun Song , Vlastimil Babka , Greg Kroah-Hartman , Oded Gabbay , Andrew Morton , Linus Torvalds , Mike Kravetz Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Extend FAULT_FLAG_UNSHARE to break COW on anything mapped into a COW (i.e., private writable) mapping and adjust the documentation accordingly. FAULT_FLAG_UNSHARE will now also break COW when encountering the shared zeropage, a pagecache page, a PFNMAP, ... inside a COW mapping, by properly replacing the mapped page/pfn by a private copy (an exclusive anonymous page). Note that only do_wp_page() needs care: hugetlb_wp() already handles FAULT_FLAG_UNSHARE correctly. wp_huge_pmd()/wp_huge_pud() also handles it correctly, for example, splitting the huge zeropage on FAULT_FLAG_UNSHARE such that we can handle FAULT_FLAG_UNSHARE on the PTE level. This change is a requirement for reliable long-term R/O pinning in COW mappings. Signed-off-by: David Hildenbrand --- include/linux/mm_types.h | 8 ++++---- mm/memory.c | 4 ---- 2 files changed, 4 insertions(+), 8 deletions(-) diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h index 834022721bc6..3f9fa01a3e24 100644 --- a/include/linux/mm_types.h +++ b/include/linux/mm_types.h @@ -965,9 +965,9 @@ typedef struct { * @FAULT_FLAG_REMOTE: The fault is not for current task/mm. * @FAULT_FLAG_INSTRUCTION: The fault was during an instruction fetch. * @FAULT_FLAG_INTERRUPTIBLE: The fault can be interrupted by non-fatal signals. - * @FAULT_FLAG_UNSHARE: The fault is an unsharing request to unshare (and mark - * exclusive) a possibly shared anonymous page that is - * mapped R/O. + * @FAULT_FLAG_UNSHARE: The fault is an unsharing request to break COW in a + * COW mapping, making sure that an exclusive anon page is + * mapped after the fault. * @FAULT_FLAG_ORIG_PTE_VALID: whether the fault has vmf->orig_pte cached. * We should only access orig_pte if this flag set. * @@ -992,7 +992,7 @@ typedef struct { * * The combination FAULT_FLAG_WRITE|FAULT_FLAG_UNSHARE is illegal. * FAULT_FLAG_UNSHARE is ignored and treated like an ordinary read fault when - * no existing R/O-mapped anonymous page is encountered. + * applied to mappings that are not COW mappings. */ enum fault_flag { FAULT_FLAG_WRITE = 1 << 0, diff --git a/mm/memory.c b/mm/memory.c index d2f9673755be..73ed83def548 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3431,10 +3431,6 @@ static vm_fault_t do_wp_page(struct vm_fault *vmf) } wp_page_reuse(vmf); return 0; - } else if (unshare) { - /* No anonymous page -> nothing to do. */ - pte_unmap_unlock(vmf->pte, vmf->ptl); - return 0; } copy: /*