linux-kernel - Re: [PATCH v19 23/30] drm/shmem-helper: Export drm_gem_shmem_get_pages_sgt

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Message-ID: <20240125100953.34340d4f@collabora.com>
Date: Thu, 25 Jan 2024 10:09:53 +0100
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Dmitry Osipenko <dmitry.osipenko@...labora.com>
Cc: David Airlie <airlied@...il.com>, Gerd Hoffmann <kraxel@...hat.com>,
 Gurchetan Singh <gurchetansingh@...omium.org>, Chia-I Wu
 <olvaffe@...il.com>, Daniel Vetter <daniel@...ll.ch>, Maarten Lankhorst
 <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>,
 Thomas Zimmermann <tzimmermann@...e.de>, Christian König
 <christian.koenig@....com>, Qiang Yu <yuq825@...il.com>, Steven Price
 <steven.price@....com>, Emma Anholt <emma@...olt.net>, Melissa Wen
 <mwen@...lia.com>, dri-devel@...ts.freedesktop.org,
 linux-kernel@...r.kernel.org, kernel@...labora.com,
 virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v19 23/30] drm/shmem-helper: Export
 drm_gem_shmem_get_pages_sgt_locked()

On Fri,  5 Jan 2024 21:46:17 +0300
Dmitry Osipenko <dmitry.osipenko@...labora.com> wrote:

> Export drm_gem_shmem_get_pages_sgt_locked() that will be used by virtio-gpu
> shrinker during GEM swap-in operation done under the held reservation lock.
> 

Nit: I'd move that patch before "drm/shmem-helper: Add common memory
shrinker", because you'll need to call
drm_gem_shmem_get_pages_locked() and
drm_gem_shmem_get_pages_sgt_locked() if you want to repopulate the MMU
page table after when an eviction happened (see my comment on patch 22).

> Reviewed-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@...labora.com>
> ---
>  drivers/gpu/drm/drm_gem_shmem_helper.c | 22 +++++++++++++++++++++-
>  include/drm/drm_gem_shmem_helper.h     |  1 +
>  2 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
> index 59cebd1e35af..8fd7851c088b 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -875,12 +875,31 @@ struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_shmem_object *shmem)
>  }
>  EXPORT_SYMBOL_GPL(drm_gem_shmem_get_sg_table);
>  
> -static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_object *shmem)
> +/**
> + * drm_gem_shmem_get_pages_sgt_locked - Provide a scatter/gather table of pinned
> + *                                      pages for a shmem GEM object
> + * @shmem: shmem GEM object
> + *
> + * This is a locked version of @drm_gem_shmem_get_sg_table that exports a
> + * scatter/gather table suitable for PRIME usage by calling the standard
> + * DMA mapping API.
> + *
> + * Drivers must hold GEM's reservation lock when using this function.
> + *
> + * Drivers who need to acquire an scatter/gather table for objects need to call
> + * drm_gem_shmem_get_pages_sgt() instead.
> + *
> + * Returns:
> + * A pointer to the scatter/gather table of pinned pages or error pointer on failure.
> + */
> +struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_object *shmem)
>  {
>  	struct drm_gem_object *obj = &shmem->base;
>  	int ret;
>  	struct sg_table *sgt;
>  
> +	dma_resv_assert_held(shmem->base.resv);
> +
>  	if (shmem->sgt)
>  		return shmem->sgt;
>  
> @@ -904,6 +923,7 @@ static struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_
>  	kfree(sgt);
>  	return ERR_PTR(ret);
>  }
> +EXPORT_SYMBOL_GPL(drm_gem_shmem_get_pages_sgt_locked);
>  
>  /**
>   * drm_gem_shmem_get_pages_sgt - Pin pages, dma map them, and return a
> diff --git a/include/drm/drm_gem_shmem_helper.h b/include/drm/drm_gem_shmem_helper.h
> index df97c11fc99a..167f00f089de 100644
> --- a/include/drm/drm_gem_shmem_helper.h
> +++ b/include/drm/drm_gem_shmem_helper.h
> @@ -149,6 +149,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem);
>  
>  struct sg_table *drm_gem_shmem_get_sg_table(struct drm_gem_shmem_object *shmem);
>  struct sg_table *drm_gem_shmem_get_pages_sgt(struct drm_gem_shmem_object *shmem);
> +struct sg_table *drm_gem_shmem_get_pages_sgt_locked(struct drm_gem_shmem_object *shmem);
>  
>  void drm_gem_shmem_print_info(const struct drm_gem_shmem_object *shmem,
>  			      struct drm_printer *p, unsigned int indent);