linux-kernel - Re: [PATCH v6] drm/virtio: Add drm

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Message-ID: <75cf3adc-400e-44a6-b653-bee1f0cb43ec@collabora.com>
Date: Sun, 2 Feb 2025 20:17:47 +0300
From: Dmitry Osipenko <dmitry.osipenko@...labora.com>
To: Ryosuke Yasuoka <ryasuoka@...hat.com>, airlied@...hat.com,
 kraxel@...hat.com, gurchetansingh@...omium.org, olvaffe@...il.com,
 maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de,
 daniel@...ll.ch, jfalempe@...hat.com
Cc: virtualization@...ts.linux.dev, linux-kernel@...r.kernel.org,
 dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v6] drm/virtio: Add drm_panic support

Hi,

On 1/30/25 12:05, Ryosuke Yasuoka wrote:
...
> +static int virtio_drm_get_scanout_buffer(struct drm_plane *plane,
> +					 struct drm_scanout_buffer *sb)
> +{
> +	struct virtio_gpu_object *bo;
> +
> +	if (!plane->state || !plane->state->fb || !plane->state->visible)
> +		return -ENODEV;
> +
> +	bo = gem_to_virtio_gpu_obj(plane->state->fb->obj[0]);
> +	if (virtio_gpu_is_vram(bo) || bo->base.base.import_attach)
> +		return -ENODEV;
> +
> +	/* try to vmap it if possible */
> +	if (!bo->base.vaddr) {
> +		int ret;
> +
> +		ret = drm_gem_shmem_vmap(&bo->base, &sb->map[0]);

drm_gem_shmem_vmap() requires BO resv to be locked, it also may invoke
drm_gem_shmem_get_pages() that sleeps. This function can't be used in
atomic context.

For the starter, let's reject !bo->base.vaddr BOs. Normally, shmem FB
BOs are always vmapped.

-- 
Best regards,
Dmitry