Re: [PATCH v1] drm/ttm: Refcount allocated tail pages

From: Dmitry Osipenko <dmitry.osipenko@collabora.com>
To: "Christian König" <christian.koenig@amd.com>,
	"David Airlie" <airlied@linux.ie>,
	"Huang Rui" <ray.huang@amd.com>,
	"Daniel Vetter" <daniel@ffwll.ch>,
	"Trigger Huang" <Trigger.Huang@gmail.com>,
	"Gert Wollny" <gert.wollny@collabora.com>,
	"Antonio Caggiano" <antonio.caggiano@collabora.com>
Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
	Dmitry Osipenko <digetx@gmail.com>,
	kvm@vger.kernel.org, kernel@collabora.com,
	virtualization@lists.linux-foundation.org
Subject: Re: [PATCH v1] drm/ttm: Refcount allocated tail pages
Date: Mon, 15 Aug 2022 13:09:11 +0300	[thread overview]
Message-ID: <134bce02-58d6-8553-bb73-42dfda18a595@collabora.com> (raw)
In-Reply-To: <8230a356-be38-f228-4a8e-95124e8e8db6@amd.com>

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.

> Please immediately stop this completely broken approach. We have
> discussed this multiple times now.

Could you please give me a link to these discussions?

-- 
Best regards,
Dmitry