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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 3C272C433DB for ; Tue, 19 Jan 2021 20:33:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D760F2310D for ; Tue, 19 Jan 2021 20:33:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728316AbhASU1U (ORCPT ); Tue, 19 Jan 2021 15:27:20 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391951AbhASU0X (ORCPT ); Tue, 19 Jan 2021 15:26:23 -0500 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DA58BC0613ED; Tue, 19 Jan 2021 12:25:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=3skarH8usgooZsIjjZg9m11Y8vaFLaunY8jfnB6wGPQ=; b=IcFHUlBLm4M8B7XITZrlaPwJZk PxLbfPfkfkOKcDtLlhfkXiUHka5CvTPb7hLgrgmT3Ja+UqcHjN9zY1H6Tmg+WZOu5IRktFRwdo/cS V9j3hg1Ow8RITENXtDtJLmBCwghrrgT8ZPHCKw/4HQvv4xpai+rfbtNKnht6rSRWFZHmep0AFdaLc WpT0BIFZXKaOI1hvNwPxLTcH2Gpj0LlBuWbpsOxA9rDZtRWPCXjXziJFZX6g2OZYB33LP00RMcFkb 3de7nf3N03r6bUtfXPBA8XywS5tDj8kVNevPplCpPm+FZKgebPUFH+9MEl3Zc+oBbVK/fmh04LESS xKXNl/dg==; Received: from willy by casper.infradead.org with local (Exim 4.94 #2 (Red Hat Linux)) id 1l1xW1-00EmeP-RV; Tue, 19 Jan 2021 20:22:22 +0000 Date: Tue, 19 Jan 2021 20:22:13 +0000 From: Matthew Wilcox To: Mike Rapoport Cc: Andrew Morton , Alexander Viro , Andy Lutomirski , Arnd Bergmann , Borislav Petkov , Catalin Marinas , Christopher Lameter , Dan Williams , Dave Hansen , David Hildenbrand , Elena Reshetova , "H. Peter Anvin" , Ingo Molnar , James Bottomley , "Kirill A. Shutemov" , Mark Rutland , Mike Rapoport , Michael Kerrisk , Palmer Dabbelt , Paul Walmsley , Peter Zijlstra , Rick Edgecombe , Roman Gushchin , Shakeel Butt , Shuah Khan , Thomas Gleixner , Tycho Andersen , Will Deacon , linux-api@vger.kernel.org, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-nvdimm@lists.01.org, linux-riscv@lists.infradead.org, x86@kernel.org, Hagen Paul Pfeifer Subject: Re: [PATCH v14 05/10] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20210119202213.GI2260413@casper.infradead.org> References: <20201203062949.5484-1-rppt@kernel.org> <20201203062949.5484-6-rppt@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201203062949.5484-6-rppt@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Thu, Dec 03, 2020 at 08:29:44AM +0200, Mike Rapoport wrote: > +static vm_fault_t secretmem_fault(struct vm_fault *vmf) > +{ > + struct address_space *mapping = vmf->vma->vm_file->f_mapping; > + struct inode *inode = file_inode(vmf->vma->vm_file); > + pgoff_t offset = vmf->pgoff; > + vm_fault_t ret = 0; > + unsigned long addr; > + struct page *page; > + int err; > + > + if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) > + return vmf_error(-EINVAL); > + > + page = find_get_page(mapping, offset); > + if (!page) { > + > + page = secretmem_alloc_page(vmf->gfp_mask); > + if (!page) > + return vmf_error(-ENOMEM); Just use VM_FAULT_OOM directly. > + err = add_to_page_cache(page, mapping, offset, vmf->gfp_mask); > + if (unlikely(err)) > + goto err_put_page; What if the error is EEXIST because somebody else raced with you to add a new page to the page cache? > + err = set_direct_map_invalid_noflush(page, 1); > + if (err) > + goto err_del_page_cache; Does this work correctly if somebody else has a reference to the page in the meantime? > + addr = (unsigned long)page_address(page); > + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); > + > + __SetPageUptodate(page); Once you've added it to the cache, somebody else can come along and try to lock it. They will set PageWaiter. Now you call __SetPageUptodate and wipe out their PageWaiter bit. So you won't wake them up when you unlock. You can call __SetPageUptodate before adding it to the page cache, but once it's visible to another thread, you can't do that. > + ret = VM_FAULT_LOCKED; > + } > + > + vmf->page = page; You're supposed to return the page locked, so use find_lock_page() instead of find_get_page(). > + return ret; > + > +err_del_page_cache: > + delete_from_page_cache(page); > +err_put_page: > + put_page(page); > + return vmf_error(err); > +}