linux-kernel - Re: [Nouveau] [PATCH drm-next 05/14] drm/nouveau: new VM

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Date:   Mon, 6 Feb 2023 17:14:54 +0100
From:   Christian König <christian.koenig@....com>
To:     Danilo Krummrich <dakr@...hat.com>, Dave Airlie <airlied@...il.com>
Cc:     Matthew Brost <matthew.brost@...el.com>, daniel@...ll.ch,
        corbet@....net, dri-devel@...ts.freedesktop.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        mripard@...nel.org, bskeggs@...hat.com, jason@...kstrand.net,
        nouveau@...ts.freedesktop.org, airlied@...hat.com
Subject: Re: [Nouveau] [PATCH drm-next 05/14] drm/nouveau: new VM_BIND uapi
 interfaces

Concentrating this discussion on a very big misunderstanding first.

Am 06.02.23 um 14:27 schrieb Danilo Krummrich:
> [SNIP]
> My understanding is that userspace is fully responsible on the parts 
> of the GPU VA space it owns. This means that userspace needs to take 
> care to *not* ask the kernel to modify mappings that are in use currently.

This is a completely wrong assumption! Take a look at what games like 
Forza Horizzon are doing.

Basically that game allocates a very big sparse area and fills it with 
pages from BOs while shaders are accessing it. And yes, as far as I know 
this is completely valid behavior.

So you need to be able to handle this case anyway and the approach with 
the regions won't help you at all preventing that.

Regards,
Christian.