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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id BAE9AC77B6E for ; Wed, 12 Apr 2023 15:45:23 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 346B510E8A3; Wed, 12 Apr 2023 15:45:23 +0000 (UTC) Received: from mga17.intel.com (mga17.intel.com [192.55.52.151]) by gabe.freedesktop.org (Postfix) with ESMTPS id 59ECF10E881; Wed, 12 Apr 2023 15:45:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1681314321; x=1712850321; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=IERnqLXMW+gb74vzXKSwdmaOj1kubqs2Fl+YWa4aSvM=; b=g7ZAKsyFcBFHPcK3vLAVdipTy132/sHTmtPZCJU/DV1fVTOTitwniDX1 Db2jsHv4TN69JmGceZzLTuiiwVmDYRBONfjybwmdLbO8JYBOzh87Tvd6B 9hUoperdql/fUGgwv9l1ZJmTao1GhAnIgIhmSlYrIlmCiIWzCW2vueKDZ /uGpybmY6VnRfa5C6Em0AlCyLZkS4PVu8VqhOExvWz0pS6WjrnvK7gCWo xbn7iMAbfMqP5uXClnEovWYkVlyF6YUSVqoWxXMgi4jcKfnymDnbE/XpZ jmS2HLzyL3eaKcQ5p3/N/ya2hWH1VA72VK6xWBQDjg18MYGIdmbD7paa5 Q==; X-IronPort-AV: E=McAfee;i="6600,9927,10678"; a="324297153" X-IronPort-AV: E=Sophos;i="5.98,339,1673942400"; d="scan'208";a="324297153" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by fmsmga107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Apr 2023 08:45:20 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10678"; a="719416191" X-IronPort-AV: E=Sophos;i="5.98,339,1673942400"; d="scan'208";a="719416191" Received: from amurkovx-mobl.ger.corp.intel.com (HELO [10.213.229.123]) ([10.213.229.123]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 12 Apr 2023 08:45:15 -0700 Message-ID: <1b341218-f0e2-a613-2ac6-107064a813ca@linux.intel.com> Date: Wed, 12 Apr 2023 16:45:13 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Content-Language: en-US To: "Fabio M. De Francesco" , Ira Weiny , Zhao Liu , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , David Airlie , Daniel Vetter , Matthew Auld , =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= , Nirmoy Das , Maarten Lankhorst , Chris Wilson , =?UTF-8?Q?Christian_K=c3=b6nig?= , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20230329073220.3982460-1-zhao1.liu@linux.intel.com> <64265ef8725fe_375f7e294a@iweiny-mobl.notmuch> <2177327.1BCLMh4Saa@suse> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: <2177327.1BCLMh4Saa@suse> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Intel-gfx] [PATCH v2 9/9] drm/i915: Use kmap_local_page() in gem/i915_gem_execbuffer.c X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Zhao Liu , Zhenyu Wang Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 31/03/2023 16:32, Fabio M. De Francesco wrote: > On venerdì 31 marzo 2023 13:30:20 CEST Tvrtko Ursulin wrote: >> On 31/03/2023 05:18, Ira Weiny wrote: >>> Zhao Liu wrote: >>>> From: Zhao Liu >>>> >>>> The use of kmap_atomic() is being deprecated in favor of >>>> kmap_local_page()[1], and this patch converts the calls from >>>> kmap_atomic() to kmap_local_page(). >>>> >>>> The main difference between atomic and local mappings is that local >>>> mappings doesn't disable page faults or preemption (the preemption is >>>> disabled for !PREEMPT_RT case, otherwise it only disables migration). >>>> >>>> With kmap_local_page(), we can avoid the often unwanted side effect of >>>> unnecessary page faults and preemption disables. >>>> >>>> In i915_gem_execbuffer.c, eb->reloc_cache.vaddr is mapped by >>>> kmap_atomic() in eb_relocate_entry(), and is unmapped by >>>> kunmap_atomic() in reloc_cache_reset(). >>> >>> First off thanks for the series and sticking with this. That said this >>> patch kind of threw me for a loop because tracing the map/unmap calls did >>> not make sense to me. See below. >>> >>>> And this mapping/unmapping occurs in two places: one is in >>>> eb_relocate_vma(), and another is in eb_relocate_vma_slow(). >>>> >>>> The function eb_relocate_vma() or eb_relocate_vma_slow() doesn't >>>> need to disable pagefaults and preemption during the above mapping/ >>>> unmapping. >>>> >>>> So it can simply use kmap_local_page() / kunmap_local() that can >>>> instead do the mapping / unmapping regardless of the context. >>>> >>>> Convert the calls of kmap_atomic() / kunmap_atomic() to >>>> kmap_local_page() / kunmap_local(). >>>> >>>> [1]: >>>> https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com >>>> >>>> v2: No code change since v1. Added description of the motivation of >>>> >>>> using kmap_local_page() and "Suggested-by" tag of Fabio. >>>> >>>> Suggested-by: Ira Weiny >>>> Suggested-by: Fabio M. De Francesco >>>> Signed-off-by: Zhao Liu >>>> --- >>>> >>>> Suggested by credits: >>>> Ira: Referred to his task document, review comments. >>>> Fabio: Referred to his boiler plate commit message and his description >>>> >>>> about why kmap_local_page() should be preferred. >>>> >>>> --- >>>> >>>> drivers/gpu/drm/i915/gem/i915_gem_execbuffer.c | 10 +++++----- >>>> 1 file changed, 5 insertions(+), 5 deletions(-) >>>> > > [snip] > >> However I am unsure if disabling pagefaulting is needed or not. Thomas, >> Matt, being the last to touch this area, perhaps you could have a look? >> Because I notice we have a fallback iomap path which still uses >> io_mapping_map_atomic_wc. So if kmap_atomic to kmap_local conversion is >> safe, does the iomap side also needs converting to >> io_mapping_map_local_wc? Or they have separate requirements? > > AFAIK, the requirements for io_mapping_map_local_wc() are the same as for > kmap_local_page(): the kernel virtual address is _only_ valid in the caller > context, and map/unmap nesting must be done in stack-based ordering (LIFO). > > I think a follow up patch could safely switch to io_mapping_map_local_wc() / > io_mapping_unmap_local_wc since the address is local to context. > > However, not being an expert, reading your note now I suspect that I'm missing > something. Can I ask why you think that page-faults disabling might be > necessary? I am not saying it is, was just unsure and wanted some people who worked on this code most recently to take a look and confirm. I guess it will work since the copying is done like this anyway: /* * This is the fast path and we cannot handle a pagefault * whilst holding the struct mutex lest the user pass in the * relocations contained within a mmaped bo. For in such a case * we, the page fault handler would call i915_gem_fault() and * we would try to acquire the struct mutex again. Obviously * this is bad and so lockdep complains vehemently. */ pagefault_disable(); copied = __copy_from_user_inatomic(r, urelocs, count * sizeof(r[0])); pagefault_enable(); if (unlikely(copied)) { remain = -EFAULT; goto out; } Comment is a bit outdated since we don't use that global "struct mutex" any longer, but in any case, if there is a page fault on the mapping where we need to recurse into i915 again to satisfy if, we seem to have code already to handle it. So kmap_local conversion I *think* can't regress anything. Patch to convert the io_mapping_map_atomic_wc can indeed come later. In terms of logistics - if we landed this series to out branch it would be queued only for 6.5. Would that work for you? Regards, Tvrtko