linux-kernel - Re: [PATCH 2/5] drm/nouveau/uvmm: Allow larger pages

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Message-ID: <CAPv6GL2DQ_wY=r4eV_V=nBGaj20HtYzRfJg==rQJtuO8Fo+HAg@mail.gmail.com>
Date: Wed, 22 Oct 2025 23:39:40 +0200
From: Mary Guillemard <mary@...y.zone>
To: Danilo Krummrich <dakr@...nel.org>
Cc: Mohamed Ahmed <mohamedahmedegypt2001@...il.com>, linux-kernel@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, 
	Faith Ekstrand <faith.ekstrand@...labora.com>, Lyude Paul <lyude@...hat.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	nouveau@...ts.freedesktop.org
Subject: Re: [PATCH 2/5] drm/nouveau/uvmm: Allow larger pages

On Wed, Oct 22, 2025 at 10:56 PM Danilo Krummrich <dakr@...nel.org> wrote:
>
> On 10/22/25 12:16 PM, Mohamed Ahmed wrote:
> > Pinging again re: review and also was asking if we can revert the
> > select_page_shift() handling back to v1 behavior with a fall-back
> > path, as it looks like there are some cases where
> > nouveau_bo_fixup_align() isn't enough;
> > https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/36450#note_3159199.
>
> I don't think we should add a fallback for something that is expected to be
> sufficient.
>
> Instead we should figure out in which exact case the WARN_ON() was hit and why.

The reason I wrote this code initially was to handle addresses
provided by userspace that aren't aligned to the page size selected
during BO creation.
This is something I did trigger when typing this patch initially with
my distro provided version of mesa (likely 25.0.x but it has been a
while)
Thomas Andersen also confirmed on nouveau irc channel that he did hit
this case with an old version of NVK and this patchset.

I think we could just remove the WARN_ON and properly document that
this was previously allowed and is there for backward compatibility.

Regards,
Mary Guillemard