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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 A7E49C2D0DB for ; Wed, 22 Jan 2020 10:30:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 85C1A20828 for ; Wed, 22 Jan 2020 10:30:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729236AbgAVKaj (ORCPT ); Wed, 22 Jan 2020 05:30:39 -0500 Received: from honk.sigxcpu.org ([24.134.29.49]:54384 "EHLO honk.sigxcpu.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728931AbgAVKaj (ORCPT ); Wed, 22 Jan 2020 05:30:39 -0500 Received: from localhost (localhost [127.0.0.1]) by honk.sigxcpu.org (Postfix) with ESMTP id 94D68FB03; Wed, 22 Jan 2020 11:30:36 +0100 (CET) X-Virus-Scanned: Debian amavisd-new at honk.sigxcpu.org Received: from honk.sigxcpu.org ([127.0.0.1]) by localhost (honk.sigxcpu.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id T6ubGSDKZvw2; Wed, 22 Jan 2020 11:30:35 +0100 (CET) Received: by bogon.sigxcpu.org (Postfix, from userid 1000) id 4AA0B404A9; Wed, 22 Jan 2020 11:30:34 +0100 (CET) Date: Wed, 22 Jan 2020 11:30:34 +0100 From: Guido =?iso-8859-1?Q?G=FCnther?= To: Arnd Bergmann Cc: Lucas Stach , Russell King , Christian Gmeiner , David Airlie , Daniel Vetter , Philipp Zabel , Sam Ravnborg , Rob Herring , Emil Velikov , The etnaviv authors , dri-devel , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] drm/etnaviv: only reject timeouts with tv_nsec >= 2 seconds Message-ID: <20200122103034.GA67385@bogon.m.sigxcpu.org> References: <20200121114553.2667556-1-arnd@arndb.de> <20200121125546.GA71415@bogon.m.sigxcpu.org> <1971902c68ff805ee0b4a66f558afe06e6edf0c5.camel@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, On Tue, Jan 21, 2020 at 08:05:27PM +0100, Arnd Bergmann wrote: > On Tue, Jan 21, 2020 at 5:10 PM Lucas Stach wrote: > > > > Hi Guido, > > > > On Di, 2020-01-21 at 13:55 +0100, Guido Günther wrote: > > > Hi, > > > On Tue, Jan 21, 2020 at 12:45:25PM +0100, Arnd Bergmann wrote: > > > > As Guido Günther reported, get_abs_timeout() in the etnaviv user space > > > > sometimes passes timeouts with nanosecond values larger than 1000000000, > > > > which gets rejected after my first patch. > > > > > > > > To avoid breaking this, while also not allowing completely arbitrary > > > > values, set the limit to 1999999999 and use set_normalized_timespec64() > > > > to get the correct format before comparing it. > > > > > > I'm seeing values up to 5 seconds so I need > > > > > > if (args->timeout.tv_nsec > (5 * NSEC_PER_SEC)) > > > > > > to unbreak rendering. Which seems to match what mesa's get_abs_timeout() > > > does and how it's invoked. > > > > I have not tested this myself yet, only looked at the code. From the > > code I quoted earlier, I don't see how we end up with 5 * NSEC_PER_SEC > > in the tv_nsec member, even if the timeout passed to get_abs_timeout() > > is 5 seconds. > > I can think of two different ways you'd end up with around five seconds here: > > a) you have a completely arbitrary 32-bit number through truncation, > which is up to 4.2 seconds > b) you have the same kind of 32-bit number, but add up to another 999999999 > nanoseconds, so you get up to 5.2 seconds in the 64-bit field. I've dumped out some values tv_nsec values with current mesa git on arm64: [ 33.699652] etnaviv_ioctl_gem_cpu_prep: 4990449401 [ 33.813081] etnaviv_ioctl_gem_cpu_prep: 5103872445 [ 33.822936] etnaviv_ioctl_gem_cpu_prep: 5113731286 [ 33.840963] etnaviv_ioctl_gem_cpu_prep: 5131762726 [ 33.854120] etnaviv_ioctl_gem_cpu_prep: 5144920127 [ 33.861426] etnaviv_ioctl_gem_cpu_prep: 5152227527 [ 33.872666] etnaviv_ioctl_gem_cpu_prep: 5163466968 [ 33.879485] etnaviv_ioctl_gem_cpu_prep: 5170286808 The problem is that in mesa/libdrm static inline void get_abs_timeout(struct drm_etnaviv_timespec *tv, uint64_t ns) { struct timespec t; uint32_t s = ns / 1000000000; clock_gettime(CLOCK_MONOTONIC, &t); tv->tv_sec = t.tv_sec + s; tv->tv_nsec = t.tv_nsec + ns - (s * 1000000000); ^^^^^^^^^^^^^^^ this overflows (since `s` is `uint_32t` and hence we substract a way too small value with ns = 5000000000 which mesa uses in etna_bo_cpu_prep. } So with current mesa/libdrm (which needs to be fixed) we'd have a maximum t.tv_nsec + ns - (s_max * 1000000000) 999999999 + 5000000000 - 705032704 = 5294967295 Does that make sense? If so that'd be the possible upper bound for the kernel. Note that this only applies to etnaviv_ioctl_gem_cpu_prep. While etnaviv_ioctl_wait_fence and etnaviv_ioctl_gem_wait are affected too i've not yet seen user space passing in larger values. Cheers, -- Guido > > It could of course be something completely different. If this works correctly > today, we may need to allow any 64-bit input for the nanoseconds and do > an expensive 64-bit div/mod in the kernel for normalization rather than the > cheaper set_normalized_timespec64() from my patch. > > Arnd >