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

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Message-ID: <134bce02-58d6-8553-bb73-42dfda18a595@collabora.com>
Date:   Mon, 15 Aug 2022 13:09:11 +0300
From:   Dmitry Osipenko <dmitry.osipenko@...labora.com>
To:     Christian König <christian.koenig@....com>,
        David Airlie <airlied@...ux.ie>, Huang Rui <ray.huang@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Trigger Huang <Trigger.Huang@...il.com>,
        Gert Wollny <gert.wollny@...labora.com>,
        Antonio Caggiano <antonio.caggiano@...labora.com>
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>, kvm@...r.kernel.org,
        kernel@...labora.com, virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v1] drm/ttm: Refcount allocated tail pages

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