Re: [PATCH 1/4] memremap: add an owner field to struct dev_pagemap

[Ralph Campbell <rcampbell@nvidia.com>]

On 3/16/20 12:32 PM, Christoph Hellwig wrote:
> Add a new opaque owner field to struct dev_pagemap, which will allow
> the hmm and migrate_vma code to identify who owns ZONE_DEVICE memory,
> and refuse to work on mappings not owned by the calling entity.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

This looks like a reasonable approach to take.
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>

> ---
>   arch/powerpc/kvm/book3s_hv_uvmem.c     | 2 ++
>   drivers/gpu/drm/nouveau/nouveau_dmem.c | 1 +
>   include/linux/memremap.h               | 4 ++++
>   mm/memremap.c                          | 4 ++++
>   4 files changed, 11 insertions(+)
> 
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 79b1202b1c62..67fefb03b9b7 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -779,6 +779,8 @@ int kvmppc_uvmem_init(void)
>   	kvmppc_uvmem_pgmap.type = MEMORY_DEVICE_PRIVATE;
>   	kvmppc_uvmem_pgmap.res = *res;
>   	kvmppc_uvmem_pgmap.ops = &kvmppc_uvmem_ops;
> +	/* just one global instance: */
> +	kvmppc_uvmem_pgmap.owner = &kvmppc_uvmem_pgmap;
>   	addr = memremap_pages(&kvmppc_uvmem_pgmap, NUMA_NO_NODE);
>   	if (IS_ERR(addr)) {
>   		ret = PTR_ERR(addr);
> diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> index 0ad5d87b5a8e..a4682272586e 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> @@ -526,6 +526,7 @@ nouveau_dmem_init(struct nouveau_drm *drm)
>   	drm->dmem->pagemap.type = MEMORY_DEVICE_PRIVATE;
>   	drm->dmem->pagemap.res = *res;
>   	drm->dmem->pagemap.ops = &nouveau_dmem_pagemap_ops;
> +	drm->dmem->pagemap.owner = drm->dev;
>   	if (IS_ERR(devm_memremap_pages(device, &drm->dmem->pagemap)))
>   		goto out_free;
>   
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 6fefb09af7c3..60d97e8fd3c0 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -103,6 +103,9 @@ struct dev_pagemap_ops {
>    * @type: memory type: see MEMORY_* in memory_hotplug.h
>    * @flags: PGMAP_* flags to specify defailed behavior
>    * @ops: method table
> + * @owner: an opaque pointer identifying the entity that manages this
> + *	instance.  Used by various helpers to make sure that no
> + *	foreign ZONE_DEVICE memory is accessed.
>    */
>   struct dev_pagemap {
>   	struct vmem_altmap altmap;
> @@ -113,6 +116,7 @@ struct dev_pagemap {
>   	enum memory_type type;
>   	unsigned int flags;
>   	const struct dev_pagemap_ops *ops;
> +	void *owner;
>   };
>   
>   static inline struct vmem_altmap *pgmap_altmap(struct dev_pagemap *pgmap)
> diff --git a/mm/memremap.c b/mm/memremap.c
> index 09b5b7adc773..9b2c97ceb775 100644
> --- a/mm/memremap.c
> +++ b/mm/memremap.c
> @@ -181,6 +181,10 @@ void *memremap_pages(struct dev_pagemap *pgmap, int nid)
>   			WARN(1, "Missing migrate_to_ram method\n");
>   			return ERR_PTR(-EINVAL);
>   		}
> +		if (!pgmap->owner) {
> +			WARN(1, "Missing owner\n");
> +			return ERR_PTR(-EINVAL);
> +		}
>   		break;
>   	case MEMORY_DEVICE_FS_DAX:
>   		if (!IS_ENABLED(CONFIG_ZONE_DEVICE) ||
>