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=-6.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 9A34DC433E6 for ; Wed, 20 Jan 2021 17:05:00 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2CDEE233ED for ; Wed, 20 Jan 2021 17:04:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2CDEE233ED Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 776A96B0005; Wed, 20 Jan 2021 12:04:59 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6FFB16B0006; Wed, 20 Jan 2021 12:04:59 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C93F6B0007; Wed, 20 Jan 2021 12:04:59 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0095.hostedemail.com [216.40.44.95]) by kanga.kvack.org (Postfix) with ESMTP id 39E7A6B0005 for ; Wed, 20 Jan 2021 12:04:59 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E686C1EE6 for ; Wed, 20 Jan 2021 17:04:58 +0000 (UTC) X-FDA: 77726778276.30.glass06_550b0042755c Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id 413C8180B3C8B for ; Wed, 20 Jan 2021 17:04:58 +0000 (UTC) X-HE-Tag: glass06_550b0042755c X-Filterd-Recvd-Size: 5127 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf34.hostedemail.com (Postfix) with ESMTP for ; Wed, 20 Jan 2021 17:04:57 +0000 (UTC) Received: by mail.kernel.org (Postfix) with ESMTPSA id A0CF0233E2; Wed, 20 Jan 2021 17:04:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1611162296; bh=va+8yzZazWv2hNG2ZtWuIyB2nJKfDd4jMqhGqRAZb7o=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Vmed0anBzGag0Z8bSuEA0Tx/cC2Rraek86TT4ZNBf5NWU9KhkSVm47/e5qYB2EgMG Hh793Ebmr7UiucCD7spwxNAAotjKclldyTVEYvY9+Om97WYeu5OqlrmkqqKdKRpINM GV6HUfz4n8Lekq7b7M91CggobdUqgDEJR05GIrgy0oOyeyO3ODydj2WcNDpe3XSGHF QplrvZQrYQPXpoJ2Cyr26Z2rsG2RRiX+lrymQWzImJfV+oWjs+Ld2e7BrF1+MXHfM+ dqmV2WkQoEQfDON1aBRr8qJafeH3vkc+RZswoi3YHDceC2JJuhHPHvpbcu02/r+uVD Qbg9LOZsR6tsA== Date: Wed, 20 Jan 2021 19:04:39 +0200 From: Mike Rapoport To: Matthew Wilcox 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: <20210120170439.GP1106298@kernel.org> References: <20201203062949.5484-1-rppt@kernel.org> <20201203062949.5484-6-rppt@kernel.org> <20210119202213.GI2260413@casper.infradead.org> <20210120150510.GO1106298@kernel.org> <20210120160210.GK2260413@casper.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210120160210.GK2260413@casper.infradead.org> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jan 20, 2021 at 04:02:10PM +0000, Matthew Wilcox wrote: > On Wed, Jan 20, 2021 at 05:05:10PM +0200, Mike Rapoport wrote: > > On Tue, Jan 19, 2021 at 08:22:13PM +0000, Matthew Wilcox wrote: > > > 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. > > > > Ok. > > > > > > + 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? > > > > Right, for -EEXIST I need a retry here, thanks. > > > > > > + 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? > > > > Yes, it does. If somebody else won the race that page was dropped from the > > direct map and this call would be essentially a nop. And anyway, the very > > next patch changes the way pages are removed from the direct map ;-) > > What I'm thinking is: > > thread A page faults > doesn't find page > allocates page > adds page to page cache > thread B page faults > does find page in page cache > set direct map invalid fails > deletes from page cache > ... ? Hmm, this is not nice indeed... -- Sincerely yours, Mike.