linux-kernel - Re: [PATCH RESEND] drm/virtio: Align host mapping request to maximum platform page size

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Message-ID: <CAMT+MTSHi26NduO4+2hc-CPwRXQ6qJ0=DwZq=4Tt1vNd7RKyvQ@mail.gmail.com>
Date: Fri, 24 Jan 2025 23:58:34 +0100
From: Sasha Finkelstein <fnkl.kernel@...il.com>
To: Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc: David Airlie <airlied@...hat.com>, Gerd Hoffmann <kraxel@...hat.com>, 
	Gurchetan Singh <gurchetansingh@...omium.org>, Chia-I Wu <olvaffe@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, Simona Vetter <simona@...ll.ch>, Sergio Lopez <slp@...hat.com>, 
	Rob Clark <robdclark@...il.com>, dri-devel@...ts.freedesktop.org, 
	virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	asahi@...ts.linux.dev
Subject: Re: [PATCH RESEND] drm/virtio: Align host mapping request to maximum
 platform page size

On Fri, 24 Jan 2025 at 23:52, Dmitry Osipenko
<dmitry.osipenko@...labora.com> wrote:
> > -     ret = drm_mm_insert_node(&vgdev->host_visible_mm, &vram->vram_node,
> > -                              bo->base.base.size);
> > +     ret = drm_mm_insert_node_generic(&vgdev->host_visible_mm, &vram->vram_node,
> > +                                      bo->base.base.size, MAX_PAGE_SIZE, 0, 0);
>
> This change only reserves extra space in the memory allocator, but
> doesn't change actual size of allocated BO. Instead, you likely need to
> replace all ALIGN(size, PAGE_SIZE) occurrences in the driver code with
> ALIGN(args->size, MAX_PAGE_SIZE)

This approach is good enough for my usecase, where the vmm can
cope with sub-page gpu allocations (by rounding up to full page),
but can't deal with non page aligned ones.