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Subject: Re: [PATCH 5/8] xen/netfront: read response from backend only once
To:     Juergen Gross <jgross@suse.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Stefano Stabellini <sstabellini@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        xen-devel@lists.xenproject.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20210513100302.22027-1-jgross@suse.com>
 <20210513100302.22027-6-jgross@suse.com>
From:   Jan Beulich <jbeulich@suse.com>
Message-ID: <c9f90370-fc02-3f05-0670-35f795c59d95@suse.com>
Date:   Mon, 17 May 2021 16:20:21 +0200
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On 13.05.2021 12:02, Juergen Gross wrote:
> In order to avoid problems in case the backend is modifying a response
> on the ring page while the frontend has already seen it, just read the
> response into a local buffer in one go and then operate on that buffer
> only.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Jan Beulich <jbeulich@suse.com>
with one remark:

> @@ -830,24 +830,22 @@ static int xennet_get_extras(struct netfront_queue *queue,
>  			break;
>  		}
>  
> -		extra = (struct xen_netif_extra_info *)
> -			RING_GET_RESPONSE(&queue->rx, ++cons);
> +		RING_COPY_RESPONSE(&queue->rx, ++cons, &extra);
>  
> -		if (unlikely(!extra->type ||
> -			     extra->type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
> +		if (unlikely(!extra.type ||
> +			     extra.type >= XEN_NETIF_EXTRA_TYPE_MAX)) {
>  			if (net_ratelimit())
>  				dev_warn(dev, "Invalid extra type: %d\n",
> -					extra->type);
> +					extra.type);
>  			err = -EINVAL;
>  		} else {
> -			memcpy(&extras[extra->type - 1], extra,
> -			       sizeof(*extra));
> +			memcpy(&extras[extra.type - 1], &extra, sizeof(extra));

Maybe take the opportunity and switch to (type safe) structure
assignment?

Jan