linux-kernel - Re: [PATCH drm-next v4 00/14] [RFC] DRM GPUVA Manager & Nouveau VM

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Date:   Thu, 15 Jun 2023 18:39:20 +0200
From:   Danilo Krummrich <dakr@...hat.com>
To:     Liam.Howlett@...cle.com
Cc:     airlied@...il.com, daniel@...ll.ch, tzimmermann@...e.de,
        mripard@...nel.org, corbet@....net, christian.koenig@....com,
        bskeggs@...hat.com, matthew.brost@...el.com,
        boris.brezillon@...labora.com, alexdeucher@...il.com,
        ogabbay@...nel.org, bagasdotme@...il.com, willy@...radead.org,
        jason@...kstrand.net, dri-devel@...ts.freedesktop.org,
        nouveau@...ts.freedesktop.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-next v4 00/14] [RFC] DRM GPUVA Manager & Nouveau
 VM_BIND UAPI

On 6/7/23 00:31, Danilo Krummrich wrote:

>    Maple Tree:
>      - Maple tree uses the 'unsinged long' type for node entries. While this
>        works for 64bit, it's incompatible with the DRM GPUVA Manager on 32bit,
>        since the DRM GPUVA Manager uses the u64 type and so do drivers using it.
>        While it's questionable whether a 32bit kernel and a > 32bit GPU address
>        space make any sense, it creates tons of compiler warnings when compiling
>        for 32bit. Maybe it makes sense to expand the maple tree API to let users
>        decide which size to pick - other ideas / proposals are welcome.

I remember you told me that the filesystem folks had some interest in a 
64-bit maple tree for a 32-bit kernel as well. Are there any news or 
plans for such a feature?

For the short term I'd probably add a feature flag to the GPUVA manager, 
where drivers explicitly need to promise not to pass in addresses 
exceeding 32-bit on a 32-bit kernel, and if they don't refuse to 
initialize the GPUVA manager on 32-bit kernels - or something similar...