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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8B4E4C25B0E for ; Mon, 15 Aug 2022 10:47:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233536AbiHOKrK (ORCPT ); Mon, 15 Aug 2022 06:47:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34064 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229445AbiHOKrH (ORCPT ); Mon, 15 Aug 2022 06:47:07 -0400 Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D99601EAC9; Mon, 15 Aug 2022 03:47:06 -0700 (PDT) Received: from [IPV6:2a00:5f00:102:0:10b3:10ff:fe5d:4ec1] (unknown [IPv6:2a00:5f00:102:0:10b3:10ff:fe5d:4ec1]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id 5882A6601BAA; Mon, 15 Aug 2022 11:47:04 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1660560425; bh=4Q0fuKDJh4SMCJxcnmsdvamWwLpHx4eVgLbDngQNTRs=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=TfIUMPVDQhkaQvgEuHwsbfs+xYUiwndQE5gfjtjam2Cd+/7Kz5vOYMqyP5A0NqMMY tpSP/0te7JTBVYBx4zjJFGPB8CaaQQ96yfePGe7dCNPV4ieHsIxUsn/LEhGMlv0TsJ eNDB7HTELwo1oxhJHy+pKzYxVQEbhHGC3hQ+JzTQvt2Yvm2qNRDAink5eO5GX4jcTJ CFCUZGtakrrFrsx062NQiYFmjqnNAVp0WUC5gJGSkb2q/lE2smd72WxymLAx9UoaUW 008064xppDHITZIlXmkwGOZbPDUYiQA3FK7M3oNkIzl8+VQuXjferLsHauq/TbORG3 KPrHxEvw7EHFQ== Message-ID: <2df57a30-2afb-23dc-c7f5-f61c113dd5b4@collabora.com> Date: Mon, 15 Aug 2022 13:47:01 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v1] drm/ttm: Refcount allocated tail pages Content-Language: en-US From: Dmitry Osipenko To: =?UTF-8?Q?Christian_K=c3=b6nig?= , David Airlie , Huang Rui , Daniel Vetter , Trigger Huang , Gert Wollny , Antonio Caggiano Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Dmitry Osipenko , kvm@vger.kernel.org, kernel@collabora.com, virtualization@lists.linux-foundation.org References: <20220815095423.11131-1-dmitry.osipenko@collabora.com> <8230a356-be38-f228-4a8e-95124e8e8db6@amd.com> <134bce02-58d6-8553-bb73-42dfda18a595@collabora.com> <8caf3008-dcf3-985a-631e-e019b277c6f0@amd.com> <4fcc4739-2da9-1b89-209c-876129604d7d@amd.com> <14be3b22-1d60-732b-c695-ddacc6b21055@collabora.com> In-Reply-To: <14be3b22-1d60-732b-c695-ddacc6b21055@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 8/15/22 13:18, Dmitry Osipenko wrote: > On 8/15/22 13:14, Christian König wrote: >> Am 15.08.22 um 12:11 schrieb Christian König: >>> Am 15.08.22 um 12:09 schrieb Dmitry Osipenko: >>>> On 8/15/22 13:05, Christian König wrote: >>>>> Am 15.08.22 um 11:54 schrieb Dmitry Osipenko: >>>>>> Higher order pages allocated using alloc_pages() aren't refcounted and >>>>>> they >>>>>> need to be refcounted, otherwise it's impossible to map them by >>>>>> KVM. This >>>>>> patch sets the refcount of the tail pages and fixes the KVM memory >>>>>> mapping >>>>>> faults. >>>>>> >>>>>> Without this change guest virgl driver can't map host buffers into >>>>>> guest >>>>>> and can't provide OpenGL 4.5 profile support to the guest. The host >>>>>> mappings are also needed for enabling the Venus driver using host GPU >>>>>> drivers that are utilizing TTM. >>>>>> >>>>>> Based on a patch proposed by Trigger Huang. >>>>> Well I can't count how often I have repeated this: This is an >>>>> absolutely >>>>> clear NAK! >>>>> >>>>> TTM pages are not reference counted in the first place and because of >>>>> this giving them to virgl is illegal. >>>> A? The first page is refcounted when allocated, the tail pages are not. >>> >>> No they aren't. The first page is just by coincident initialized with >>> a refcount of 1. This refcount is completely ignored and not used at all. >>> >>> Incrementing the reference count and by this mapping the page into >>> some other address space is illegal and corrupts the internal state >>> tracking of TTM. >> >> See this comment in the source code as well: >> >>         /* Don't set the __GFP_COMP flag for higher order allocations. >>          * Mapping pages directly into an userspace process and calling >>          * put_page() on a TTM allocated page is illegal. >>          */ >> >> I have absolutely no idea how somebody had the idea he could do this. > > I saw this comment, but it doesn't make sense because it doesn't explain > why it's illegal. Hence it looks like a bogus comment since the > refcouting certainly works, at least to a some degree because I haven't > noticed any problems in practice, maybe by luck :) > > I'll try to dig out the older discussions, thank you for the quick reply! Are you sure it was really discussed in public previously? All I can find is yours two answers to a similar patches where you're saying that this it's a wrong solution without in-depth explanation and further discussions. Maybe it was discussed privately? In this case I will be happy to get more info from you about the root of the problem so I could start to look at how to fix it properly. It's not apparent where the problem is to a TTM newbie like me. -- Best regards, Dmitry 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 7D412C00140 for ; Mon, 15 Aug 2022 10:47:51 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 5ACE510E36B; Mon, 15 Aug 2022 10:47:38 +0000 (UTC) Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by gabe.freedesktop.org (Postfix) with ESMTPS id BCBFAB2813 for ; Mon, 15 Aug 2022 10:47:06 +0000 (UTC) Received: from [IPV6:2a00:5f00:102:0:10b3:10ff:fe5d:4ec1] (unknown [IPv6:2a00:5f00:102:0:10b3:10ff:fe5d:4ec1]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id 5882A6601BAA; Mon, 15 Aug 2022 11:47:04 +0100 (BST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1660560425; bh=4Q0fuKDJh4SMCJxcnmsdvamWwLpHx4eVgLbDngQNTRs=; h=Date:Subject:From:To:Cc:References:In-Reply-To:From; b=TfIUMPVDQhkaQvgEuHwsbfs+xYUiwndQE5gfjtjam2Cd+/7Kz5vOYMqyP5A0NqMMY tpSP/0te7JTBVYBx4zjJFGPB8CaaQQ96yfePGe7dCNPV4ieHsIxUsn/LEhGMlv0TsJ eNDB7HTELwo1oxhJHy+pKzYxVQEbhHGC3hQ+JzTQvt2Yvm2qNRDAink5eO5GX4jcTJ CFCUZGtakrrFrsx062NQiYFmjqnNAVp0WUC5gJGSkb2q/lE2smd72WxymLAx9UoaUW 008064xppDHITZIlXmkwGOZbPDUYiQA3FK7M3oNkIzl8+VQuXjferLsHauq/TbORG3 KPrHxEvw7EHFQ== Message-ID: <2df57a30-2afb-23dc-c7f5-f61c113dd5b4@collabora.com> Date: Mon, 15 Aug 2022 13:47:01 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.12.0 Subject: Re: [PATCH v1] drm/ttm: Refcount allocated tail pages Content-Language: en-US From: Dmitry Osipenko To: =?UTF-8?Q?Christian_K=c3=b6nig?= , David Airlie , Huang Rui , Daniel Vetter , Trigger Huang , Gert Wollny , Antonio Caggiano References: <20220815095423.11131-1-dmitry.osipenko@collabora.com> <8230a356-be38-f228-4a8e-95124e8e8db6@amd.com> <134bce02-58d6-8553-bb73-42dfda18a595@collabora.com> <8caf3008-dcf3-985a-631e-e019b277c6f0@amd.com> <4fcc4739-2da9-1b89-209c-876129604d7d@amd.com> <14be3b22-1d60-732b-c695-ddacc6b21055@collabora.com> In-Reply-To: <14be3b22-1d60-732b-c695-ddacc6b21055@collabora.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, virtualization@lists.linux-foundation.org, Dmitry Osipenko , kernel@collabora.com Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 8/15/22 13:18, Dmitry Osipenko wrote: > On 8/15/22 13:14, Christian König wrote: >> Am 15.08.22 um 12:11 schrieb Christian König: >>> Am 15.08.22 um 12:09 schrieb Dmitry Osipenko: >>>> On 8/15/22 13:05, Christian König wrote: >>>>> Am 15.08.22 um 11:54 schrieb Dmitry Osipenko: >>>>>> Higher order pages allocated using alloc_pages() aren't refcounted and >>>>>> they >>>>>> need to be refcounted, otherwise it's impossible to map them by >>>>>> KVM. This >>>>>> patch sets the refcount of the tail pages and fixes the KVM memory >>>>>> mapping >>>>>> faults. >>>>>> >>>>>> Without this change guest virgl driver can't map host buffers into >>>>>> guest >>>>>> and can't provide OpenGL 4.5 profile support to the guest. The host >>>>>> mappings are also needed for enabling the Venus driver using host GPU >>>>>> drivers that are utilizing TTM. >>>>>> >>>>>> Based on a patch proposed by Trigger Huang. >>>>> Well I can't count how often I have repeated this: This is an >>>>> absolutely >>>>> clear NAK! >>>>> >>>>> TTM pages are not reference counted in the first place and because of >>>>> this giving them to virgl is illegal. >>>> A? The first page is refcounted when allocated, the tail pages are not. >>> >>> No they aren't. The first page is just by coincident initialized with >>> a refcount of 1. This refcount is completely ignored and not used at all. >>> >>> Incrementing the reference count and by this mapping the page into >>> some other address space is illegal and corrupts the internal state >>> tracking of TTM. >> >> See this comment in the source code as well: >> >>         /* Don't set the __GFP_COMP flag for higher order allocations. >>          * Mapping pages directly into an userspace process and calling >>          * put_page() on a TTM allocated page is illegal. >>          */ >> >> I have absolutely no idea how somebody had the idea he could do this. > > I saw this comment, but it doesn't make sense because it doesn't explain > why it's illegal. Hence it looks like a bogus comment since the > refcouting certainly works, at least to a some degree because I haven't > noticed any problems in practice, maybe by luck :) > > I'll try to dig out the older discussions, thank you for the quick reply! Are you sure it was really discussed in public previously? All I can find is yours two answers to a similar patches where you're saying that this it's a wrong solution without in-depth explanation and further discussions. Maybe it was discussed privately? In this case I will be happy to get more info from you about the root of the problem so I could start to look at how to fix it properly. It's not apparent where the problem is to a TTM newbie like me. -- Best regards, Dmitry