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=-0.8 required=3.0 tests=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 093B7C433DF for ; Tue, 2 Jun 2020 16:30:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7E2920738 for ; Tue, 2 Jun 2020 16:30:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727782AbgFBQav (ORCPT ); Tue, 2 Jun 2020 12:30:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49812 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726162AbgFBQav (ORCPT ); Tue, 2 Jun 2020 12:30:51 -0400 Received: from ZenIV.linux.org.uk (zeniv.linux.org.uk [IPv6:2002:c35c:fd02::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85261C05BD1E; Tue, 2 Jun 2020 09:30:50 -0700 (PDT) Received: from viro by ZenIV.linux.org.uk with local (Exim 4.93 #3 (Red Hat Linux)) id 1jg9oO-0021bx-FW; Tue, 02 Jun 2020 16:30:48 +0000 Date: Tue, 2 Jun 2020 17:30:48 +0100 From: Al Viro To: "Michael S. Tsirkin" Cc: linux-kernel@vger.kernel.org, Jason Wang , netdev@vger.kernel.org Subject: Re: [PATCH RFC] uaccess: user_access_begin_after_access_ok() Message-ID: <20200602163048.GL23230@ZenIV.linux.org.uk> References: <20200602084257.134555-1-mst@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200602084257.134555-1-mst@redhat.com> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Jun 02, 2020 at 04:45:05AM -0400, Michael S. Tsirkin wrote: > So vhost needs to poke at userspace *a lot* in a quick succession. It > is thus benefitial to enable userspace access, do our thing, then > disable. Except access_ok has already been pre-validated with all the > relevant nospec checks, so we don't need that. Add an API to allow > userspace access after access_ok and barrier_nospec are done. This is the wrong way to do it, and this API is certain to be abused elsewhere. NAK - we need to sort out vhost-related problems, but this is not an acceptable solution. Sorry.