From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Vetter Subject: Re: [PATCH 39/48] drm/i915: Do not allow buffers at offset 0 Date: Wed, 18 Dec 2013 15:58:09 +0100 Message-ID: <20131218145809.GL26371@phenom.ffwll.local> References: <20131206215521.GA6922@bwidawsk.net> <1386367941-7131-1-git-send-email-benjamin.widawsky@intel.com> <1386367941-7131-39-git-send-email-benjamin.widawsky@intel.com> <20131212105903.GF6195@nuc-i3427.alporthouse.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-ee0-f43.google.com (mail-ee0-f43.google.com [74.125.83.43]) by gabe.freedesktop.org (Postfix) with ESMTP id 8BA3AFA648 for ; Wed, 18 Dec 2013 06:57:16 -0800 (PST) Received: by mail-ee0-f43.google.com with SMTP id c13so3596976eek.30 for ; Wed, 18 Dec 2013 06:57:15 -0800 (PST) Content-Disposition: inline In-Reply-To: <20131212105903.GF6195@nuc-i3427.alporthouse.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Chris Wilson , Ben Widawsky , Intel GFX , Ben Widawsky List-Id: intel-gfx@lists.freedesktop.org On Thu, Dec 12, 2013 at 10:59:03AM +0000, Chris Wilson wrote: > On Fri, Dec 06, 2013 at 02:11:24PM -0800, Ben Widawsky wrote: > > This is primarily a band aid for an unexplainable error in > > gem_reloc_vs_gpu/forked-faulting-reloc-thrashing. Essentially as soon as > > a relocated buffer (which had a non-zero presumed offset) moved to > > offset 0, something goes bad. Since I have been unable to solve this, > > and potentially this is a good thing to do anyway, since many things can > > accidentally write to offset 0, why not? > > A better hack would have been to exclude the first page from the vm->mm, > so that we didn't then introduce a change to ggtt. Band aids need to come with much better explanations. Also, if we really want a guard area it should be of sufficient size to avoid scribbling over random gunk. With 4k screens that means about 32MB. I'll smash a revert for this patch on top of the series. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch