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Subject: Re: [PATCH 1/2] xen/xenbus: avoid large structs and arrays on the
 stack
To:     Juergen Gross <jgross@suse.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com
Cc:     Stefano Stabellini <sstabellini@kernel.org>,
        Arnd Bergmann <arnd@arndb.de>
References: <20200511073151.19043-1-jgross@suse.com>
 <20200511073151.19043-2-jgross@suse.com>
From:   Boris Ostrovsky <boris.ostrovsky@oracle.com>
Message-ID: <965e1d65-3a0c-3a71-ca58-2b5c04f98bce@oracle.com>
Date:   Mon, 11 May 2020 14:01:00 -0400
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On 5/11/20 3:31 AM, Juergen Gross wrote:
> =20
>  static int xenbus_map_ring_valloc_hvm(struct xenbus_device *dev,


I wonder whether we can drop valloc/vfree from xenbus_ring_ops' names.


> +				      struct map_ring_valloc *info,
>  				      grant_ref_t *gnt_ref,
>  				      unsigned int nr_grefs,
>  				      void **vaddr)
>  {
> -	struct xenbus_map_node *node;
> +	struct xenbus_map_node *node =3D info->node;
>  	int err;
>  	void *addr;
>  	bool leaked =3D false;
> -	struct map_ring_valloc_hvm info =3D {
> -		.idx =3D 0,
> -	};
>  	unsigned int nr_pages =3D XENBUS_PAGES(nr_grefs);
> =20
> -	if (nr_grefs > XENBUS_MAX_RING_GRANTS)
> -		return -EINVAL;
> -
> -	*vaddr =3D NULL;
> -
> -	node =3D kzalloc(sizeof(*node), GFP_KERNEL);
> -	if (!node)
> -		return -ENOMEM;
> -
>  	err =3D alloc_xenballooned_pages(nr_pages, node->hvm.pages);
>  	if (err)
>  		goto out_err;
> =20
>  	gnttab_foreach_grant(node->hvm.pages, nr_grefs,
>  			     xenbus_map_ring_setup_grant_hvm,
> -			     &info);
> +			     info);
> =20
>  	err =3D __xenbus_map_ring(dev, gnt_ref, nr_grefs, node->handles,
> -				info.phys_addrs, GNTMAP_host_map, &leaked);
> +				info, GNTMAP_host_map, &leaked);
>  	node->nr_handles =3D nr_grefs;
> =20
>  	if (err)
> @@ -641,11 +654,13 @@ static int xenbus_map_ring_valloc_hvm(struct xenb=
us_device *dev,
>  	spin_unlock(&xenbus_valloc_lock);
> =20
>  	*vaddr =3D addr;
> +	info->node =3D NULL;


Is this so that xenbus_map_ring_valloc() doesn't free it accidentally?


-boris


> +
>  	return 0;
> =20
> =20


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