From nobody Tue Apr 7 14:19:47 2026 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 03049C433FE for ; Mon, 17 Oct 2022 09:32:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229788AbiJQJcg (ORCPT ); Mon, 17 Oct 2022 05:32:36 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42718 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231225AbiJQJc2 (ORCPT ); Mon, 17 Oct 2022 05:32:28 -0400 Received: from mga14.intel.com (mga14.intel.com [192.55.52.115]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ADDC941D03 for ; Mon, 17 Oct 2022 02:32:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1665999147; x=1697535147; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=tiW6Fpm0hVgB6aQj9aJLze7KS0YilKpmQTotRlfBNY0=; b=byAIm+CZyqpTzAvFjOrdoEfFq1gPFEXGD2l04JB16wzJKzd0NHZoP/GN JiUy9STG+cSEMWAIJa1qAluPP11aa6hqBQTno6G2aAehNqhctoEVWV19u qj1o3pfk55vYhaVKVaC3pAgCkvuYbXHGIKfcbozNTASnLYv/YH8TGvEhD k0bIGc7W/69qubuimCi8e8Xbv4zRAPUUJz0U2tPUXhLXi5XMEm23gfj5+ 8DJCziH9HnNuMAeNGdQ9FhA40uGmMuEK/uyBuBMVAjBW9yo5wq8uw+xaJ lJviY/ZAJB8m8PKkT5Uro5P8aytCrtwG9ybytQdwMrvzSwWuvEaawTTUh w==; X-IronPort-AV: E=McAfee;i="6500,9779,10502"; a="305741556" X-IronPort-AV: E=Sophos;i="5.95,191,1661842800"; d="scan'208";a="305741556" Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Oct 2022 02:32:27 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6500,9779,10502"; a="717431213" X-IronPort-AV: E=Sophos;i="5.95,191,1661842800"; d="scan'208";a="717431213" Received: from liuzhao-optiplex-7080.sh.intel.com ([10.239.160.132]) by FMSMGA003.fm.intel.com with ESMTP; 17 Oct 2022 02:32:23 -0700 From: Zhao Liu To: Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , David Airlie , Daniel Vetter , Matthew Auld , =?UTF-8?q?Thomas=20Hellstr=C3=B6m?= , Nirmoy Das , Maarten Lankhorst , Chris Wilson , =?UTF-8?q?Christian=20K=C3=B6nig?= , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Cc: Ira Weiny , "Fabio M . De Francesco" , Zhenyu Wang , Zhao Liu , Dave Hansen Subject: [PATCH 1/9] drm/i915: Use kmap_local_page() in gem/i915_gem_object.c Date: Mon, 17 Oct 2022 17:37:17 +0800 Message-Id: <20221017093726.2070674-2-zhao1.liu@linux.intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20221017093726.2070674-1-zhao1.liu@linux.intel.com> References: <20221017093726.2070674-1-zhao1.liu@linux.intel.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Zhao Liu The use of kmap_atomic() is being deprecated in favor of kmap_local_page()[1]. The main difference between atomic and local mappings is that local mappings doesn't disable page faults or preemption. There're 2 reasons why i915_gem_object_read_from_page_kmap() doesn't need to disable pagefaults and preemption for mapping: 1. The flush operation is safe for CPU hotplug when preemption is not disabled. In drm/i915/gem/i915_gem_object.c, the function i915_gem_object_read_from_page_kmap() calls drm_clflush_virt_range() to use CLFLUSHOPT or WBINVD to flush. Since CLFLUSHOPT is global on x86 and WBINVD is called on each cpu in drm_clflush_virt_range(), the flush operation is global and any issue with cpu's being added or removed can be handled safely. 2. Any context switch caused by preemption or sleep (pagefault may cause sleep) doesn't affect the validity of local mapping. Therefore, i915_gem_object_read_from_page_kmap() is a function where the use of kmap_local_page() in place of kmap_atomic() is correctly suited. Convert the calls of kmap_atomic() / kunmap_atomic() to kmap_local_page() / kunmap_local(). And remove the redundant variable that stores the address of the mapped page since kunmap_local() can accept any pointer within the page. [1]: https://lore.kernel.org/all/20220813220034.806698-1-ira.weiny@intel.com Suggested-by: Dave Hansen Suggested-by: Ira Weiny Suggested-by: Fabio M. De Francesco Signed-off-by: Zhao Liu --- Suggested by credits: Dave: Referred to his explanation about cache flush. Ira: Referred to his task document, review comments and explanation about cache flush. Fabio: Referred to his boiler plate commit message. --- drivers/gpu/drm/i915/gem/i915_gem_object.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i= 915/gem/i915_gem_object.c index 369006c5317f..a0072abed75e 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c @@ -413,17 +413,15 @@ void __i915_gem_object_invalidate_frontbuffer(struct = drm_i915_gem_object *obj, static void i915_gem_object_read_from_page_kmap(struct drm_i915_gem_object *obj, u64 o= ffset, void *dst, int size) { - void *src_map; void *src_ptr; =20 - src_map =3D kmap_atomic(i915_gem_object_get_page(obj, offset >> PAGE_SHIF= T)); - - src_ptr =3D src_map + offset_in_page(offset); + src_ptr =3D kmap_local_page(i915_gem_object_get_page(obj, offset >> PAGE_= SHIFT)) + + offset_in_page(offset); if (!(obj->cache_coherent & I915_BO_CACHE_COHERENT_FOR_READ)) drm_clflush_virt_range(src_ptr, size); memcpy(dst, src_ptr, size); =20 - kunmap_atomic(src_map); + kunmap_local(src_ptr); } =20 static void --=20 2.34.1