Re: Sub page Grant Table mappings

[David Vrabel <david.vrabel@citrix.com>]

On 22/12/15 20:59, Mike Belopuhov wrote:
> Hi,
> 
> I'm trying to get grant table sub page mappings working on Xen 4.5.
> I know there have been some changes in the trunk regarding moving src/
> dst checks closer together, but I can't test this easily atm.  Please
> bear with me for a moment.  Or tell me that it might have been broken
> previously.
> 
> What I'm trying to do is to map in a 2k cluster from the networking
> stack (we call it an mbuf cluster, you might call it skb something)
> onto the Netfront Rx ring.  2 clusters fit one page.  Therefore for
> one frame address which is a (PA >> 12) I might have 2 entries one
> after the other, both with sub_page.length = 2048 but one with a
> sub_page.page_off = 2048 and the other with a 0 offset.  Both come
> with (GTF_permit_access | GTF_sub_page) flags.

The netif protocol doesn't allow subpages for Rx requests -- the backend
requires a full page to be granted.  Note how struct netif_rx_req only
has id and gref fields.

David