linux-kernel - Re: [PATCH v3 0/2] drm/panic: Add support to scanout buffer as array of pages

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Message-ID: <009a1a7b-594b-4709-b9bc-068b2e6aa922@redhat.com>
Date: Thu, 10 Apr 2025 11:06:47 +0200
From: Jocelyn Falempe <jfalempe@...hat.com>
To: 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>,
 Ryosuke Yasuoka <ryasuoka@...hat.com>,
 Javier Martinez Canillas <javierm@...hat.com>,
 Wei Yang <richard.weiyang@...il.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 David Hildenbrand <david@...hat.com>, John Ogness
 <john.ogness@...utronix.de>, Thomas Gleixner <tglx@...utronix.de>,
 linux-mm@...ck.org, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] drm/panic: Add support to scanout buffer as array
 of pages

On 07/04/2025 15:42, Jocelyn Falempe wrote:
> Some drivers like virtio-gpu, don't map the scanout buffer in the
> kernel. Calling vmap() in a panic handler is not safe, and writing an
> atomic_vmap() API is more complex than expected [1].
> So instead, pass the array of pages of the scanout buffer to the
> panic handler, and map only one page at a time to draw the pixels.
> This is obviously slow, but acceptable for a panic handler.
> As kmap_local_page() is not safe to call from a panic handler,
> introduce a kmap_local_page_try_from_panic() that will avoid unsafe
> operations.

I applied both patches to drm-misc/drm-misc-next.

Thanks for the reviews.

> 
> [1] https://lore.kernel.org/dri-devel/20250305152555.318159-1-ryasuoka@redhat.com/
> 
> v2:
>   * Add kmap_local_page_try_from_panic() (Simona Vetter)
>   * Correctly handle the case if kmap_local_page_try_from_panic()
>     returns NULL
>   * Check that the current page is not NULL before trying to map it.
>   * Add a comment in struct drm_scanout_buffer, that the array of
>     pages shouldn't be allocated in the get_scanout_buffer() callback.
> 
> v3:
>   * Replace DRM_WARN_ONCE with pr_debug_once (Simona Vetter)
>   * Add a comment in kmap_local_page_try_from_panic() (Thomas Gleixner)
> 
> Jocelyn Falempe (2):
>    mm/kmap: Add kmap_local_page_try_from_panic()
>    drm/panic: Add support to scanout buffer as array of pages
> 
>   drivers/gpu/drm/drm_panic.c      | 142 +++++++++++++++++++++++++++++--
>   include/drm/drm_panic.h          |  12 ++-
>   include/linux/highmem-internal.h |  13 +++
>   3 files changed, 160 insertions(+), 7 deletions(-)
> 
> 
> base-commit: fbe43810d563a293e3de301141d33caf1f5d5c5a