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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0CA5FC004D4 for ; Sat, 21 Jan 2023 13:31:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229780AbjAUNbn (ORCPT ); Sat, 21 Jan 2023 08:31:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46794 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229617AbjAUNbh (ORCPT ); Sat, 21 Jan 2023 08:31:37 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 522C11EFFF for ; Sat, 21 Jan 2023 05:30:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674307855; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=cXm8Pm2BadAWYr5hSrE/IvaR3sVGcjvJzTtpdOs1lcg=; b=QLmmDlLx4K5HryZrP0kCtwbk+GW01YzfISul8IV9+89Uew0lsx0Yj+OfcQoYsv7U2PJuvl 9awRHvnT4YxMB/x1HP6ujk38QIda7IDz2vLEsvf4LtOgeZ2vny7ampX5b4QaoE5qcMt2DQ Wu+wTR+DXoCUyUdZsW2Ivqu05Mvvkxg= 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-379-Pm5zKtl0PO-PRws9-C3mdw-1; Sat, 21 Jan 2023 08:30:50 -0500 X-MC-Unique: Pm5zKtl0PO-PRws9-C3mdw-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 80AE31C0512D; Sat, 21 Jan 2023 13:30:49 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.33.36.23]) by smtp.corp.redhat.com (Postfix) with ESMTP id DA07B1121315; Sat, 21 Jan 2023 13:30:47 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <20230120175556.3556978-1-dhowells@redhat.com> <20230120175556.3556978-3-dhowells@redhat.com> To: Christoph Hellwig Cc: dhowells@redhat.com, Al Viro , Matthew Wilcox , Jens Axboe , Jan Kara , Jeff Layton , Logan Gunthorpe , linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , John Hubbard , linux-mm@kvack.org Subject: Re: [PATCH v7 2/8] iov_iter: Add a function to extract a page list from an iterator MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <3598254.1674307847.1@warthog.procyon.org.uk> Date: Sat, 21 Jan 2023 13:30:47 +0000 Message-ID: <3598255.1674307847@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Christoph Hellwig wrote: > On Fri, Jan 20, 2023 at 05:55:50PM +0000, David Howells wrote: > > (3) Any other sort of iterator. > > > > No refs or pins are obtained on the page, the assumption is made that > > the caller will manage page retention. ITER_ALLOW_P2PDMA is not > > permitted. > > The ITER_ALLOW_P2PDMA check here is fundamentally wrong and will > break things like io_uring to fixed buffers on NVMe. ITER_ALLOW_P2PDMA > should strictly increase the group of acceptable iters, it does must > not restrict anything. So just drop the check? Or do I actually need to do something to the pages to make it work? If I understand the code correctly, it's not actually operable right now on any page that doesn't have an appropriately marked PTE. David