linux-kernel - Re: [PATCH v5] drm/virtio: Add drm

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Message-ID: <b3fe0f90-761b-4dea-aa43-e7187a2ffd5a@collabora.com>
Date: Mon, 3 Feb 2025 04:07:13 +0300
From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
To: Jocelyn Falempe <jfalempe@...hat.com>,
 Ryosuke Yasuoka <ryasuoka@...hat.com>, airlied@...hat.com,
 kraxel@...hat.com, maarten.lankhorst@...ux.intel.com, mripard@...nel.org,
 tzimmermann@...e.de, daniel@...ll.ch, christophe.jaillet@...adoo.fr
Cc: virtualization@...ts.linux.dev, spice-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v5] drm/virtio: Add drm_panic support

On 12/2/24 20:19, Jocelyn Falempe wrote:
>>>
>>> I've now noticed that drm_gem_shmem_vmap() expects BO reservation lock
>>> to be held and we can't take lock it at a panic time.
>>>
>>> https://elixir.bootlin.com/linux/v6.12.1/source/drivers/gpu/drm/
>>> drm_gem_shmem_helper.c#L330
>>>
>>> This resv warning isn't triggered because bo->base.vaddr is set for VT
>>> framebufffer BO when panic happens.
> 
> I usually test using gnome desktop in the VM, and in this case vaddr is
> not set, and calling vmap() is needed. (and I don't get the warning, I
> will check why).

All those get_pages() and vmap() that drm_gem_shmem_vmap() uses may
sleep. You'll need to add atomic variants for the vmap funcs if it's
really needed.

Like I said in the comment to v6, let's start with rejecting BOs that
aren't vmapped. If atomic vmap will become needed, it will be a separate
problem to solve.

-- 
Best regards,
Dmitry