linux-kernel - Re: [PATCH 0/2] drm/virtio: introduce the HOST_PAGE

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Message-ID: <942afa37-a24c-48ed-ae10-c811849165bf@collabora.com>
Date: Wed, 24 Jul 2024 22:00:31 +0300
From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
To: Sergio Lopez <slp@...hat.com>, gurchetansingh@...omium.org,
 tzimmermann@...e.de, mripard@...nel.org, olvaffe@...il.com,
 kraxel@...hat.com, daniel@...ll.ch, maarten.lankhorst@...ux.intel.com,
 airlied@...hat.com
Cc: linux-kernel@...r.kernel.org, virtualization@...ts.linux.dev,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH 0/2] drm/virtio: introduce the HOST_PAGE_SIZE feature

On 7/23/24 14:49, Sergio Lopez wrote:
> There's an incresing number of machines supporting multiple page sizes
> and on these machines the host and a guest can be running, each one,
> with a different page size.
> 
> For what pertains to virtio-gpu, this is not a problem if the page size
> of the guest happens to be bigger or equal than the host, but will
> potentially lead to failures in memory allocations and/or mappings
> otherwise.

Please describe concrete problem you're trying to solve. Guest memory
allocation consists of guest pages, I don't see how knowledge of host
page size helps anything in userspace.

I suspect you want this for host blobs, but then it should be
virtio_gpu_vram_create() that should use max(host_page_sz,
guest_page_size), AFAICT. It's kernel who is responsible for memory
management, userspace can't be trusted for doing that.

-- 
Best regards,
Dmitry