Re: [Xen-devel] [PATCH 1/5] xen/netback: Use xenballooned pages for comms

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2011-10-18 at 21:26 +0100, Daniel De Graaf wrote:
> For proper grant mappings, HVM guests require pages allocated using
> alloc_xenballooned_pages instead of alloc_vm_area.
> 
> Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
> ---
>  drivers/net/xen-netback/common.h  |    4 ++--
>  drivers/net/xen-netback/netback.c |   34 ++++++++++++++++++++--------------
>  2 files changed, 22 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/net/xen-netback/common.h 
> b/drivers/net/xen-netback/common.h
> index 161f207..d5ee9d1 100644
> --- a/drivers/net/xen-netback/common.h
> +++ b/drivers/net/xen-netback/common.h
> @@ -70,8 +70,8 @@ struct xenvif {
>       /* The shared rings and indexes. */
>       struct xen_netif_tx_back_ring tx;
>       struct xen_netif_rx_back_ring rx;
> -     struct vm_struct *tx_comms_area;
> -     struct vm_struct *rx_comms_area;
> +     struct page *tx_comms_page;
> +     struct page *rx_comms_page;

This will conflict with David Vrabel's patch "net: xen-netback: use API
provided by xenbus module to map rings", which I've just noticed hasn't
been committed anywhere.

I suspect that building on David's patches (that series does something
similar to blkback too) will greatly simplify this one since you can
just patch xenbus_map_ring_valloc and friends.

Could you also explain where the requirement to use xenballooned pages
and not alloc_vm_area comes from in your commit message.

David, I guess you should resend your series now that everyone is happy
with it. If you cc the netback one to netdev@ with my Ack then Dave
Miller will pick it up into his tree (it stands alone, right?). The
blkback and grant-table ones go via Konrad I think. I suspect the last
one needs to go via akpm, or at least with his Ack.

>  
>       /* Frontend feature information. */
>       u8 can_sg:1;
> diff --git a/drivers/net/xen-netback/netback.c 
> b/drivers/net/xen-netback/netback.c
> index fd00f25..f35e07c 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -42,6 +42,7 @@
>  
>  #include <xen/events.h>
>  #include <xen/interface/memory.h>
> +#include <xen/balloon.h>
>  
>  #include <asm/xen/hypercall.h>
>  #include <asm/xen/page.h>
> @@ -1578,9 +1579,11 @@ static int xen_netbk_kthread(void *data)
>  void xen_netbk_unmap_frontend_rings(struct xenvif *vif)
>  {
>       struct gnttab_unmap_grant_ref op;
> +     void *addr;
>  
>       if (vif->tx.sring) {
> -             gnttab_set_unmap_op(&op, (unsigned 
> long)vif->tx_comms_area->addr,
> +             addr = pfn_to_kaddr(page_to_pfn(vif->tx_comms_page));
> +             gnttab_set_unmap_op(&op, (unsigned long)addr,
>                                   GNTMAP_host_map, vif->tx_shmem_handle);
>  
>               if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
> @@ -1588,16 +1591,17 @@ void xen_netbk_unmap_frontend_rings(struct xenvif 
> *vif)
>       }
>  
>       if (vif->rx.sring) {
> -             gnttab_set_unmap_op(&op, (unsigned 
> long)vif->rx_comms_area->addr,
> +             addr = pfn_to_kaddr(page_to_pfn(vif->rx_comms_page));
> +             gnttab_set_unmap_op(&op, (unsigned long)addr,
>                                   GNTMAP_host_map, vif->rx_shmem_handle);
>  
>               if (HYPERVISOR_grant_table_op(GNTTABOP_unmap_grant_ref, &op, 1))
>                       BUG();
>       }
> -     if (vif->rx_comms_area)
> -             free_vm_area(vif->rx_comms_area);
> -     if (vif->tx_comms_area)
> -             free_vm_area(vif->tx_comms_area);
> +     if (vif->rx_comms_page)
> +             free_xenballooned_pages(1, &vif->rx_comms_page);
> +     if (vif->tx_comms_page)
> +             free_xenballooned_pages(1, &vif->tx_comms_page);
>  }
>  
>  int xen_netbk_map_frontend_rings(struct xenvif *vif,
> @@ -1610,15 +1614,19 @@ int xen_netbk_map_frontend_rings(struct xenvif *vif,
>  
>       int err = -ENOMEM;
>  
> -     vif->tx_comms_area = alloc_vm_area(PAGE_SIZE);
> -     if (vif->tx_comms_area == NULL)
> +     if (alloc_xenballooned_pages(1, &vif->tx_comms_page))
>               goto err;
>  
> -     vif->rx_comms_area = alloc_vm_area(PAGE_SIZE);
> -     if (vif->rx_comms_area == NULL)
> +     txs = (struct xen_netif_tx_sring *)pfn_to_kaddr(page_to_pfn(
> +                     vif->tx_comms_page));
> +
> +     if (alloc_xenballooned_pages(1, &vif->rx_comms_page))
>               goto err;
>  
> -     gnttab_set_map_op(&op, (unsigned long)vif->tx_comms_area->addr,
> +     rxs = (struct xen_netif_rx_sring *)pfn_to_kaddr(page_to_pfn(
> +                     vif->rx_comms_page));
> +
> +     gnttab_set_map_op(&op, (unsigned long)txs,
>                         GNTMAP_host_map, tx_ring_ref, vif->domid);
>  
>       if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
> @@ -1635,10 +1643,9 @@ int xen_netbk_map_frontend_rings(struct xenvif *vif,
>       vif->tx_shmem_ref    = tx_ring_ref;
>       vif->tx_shmem_handle = op.handle;
>  
> -     txs = (struct xen_netif_tx_sring *)vif->tx_comms_area->addr;
>       BACK_RING_INIT(&vif->tx, txs, PAGE_SIZE);
>  
> -     gnttab_set_map_op(&op, (unsigned long)vif->rx_comms_area->addr,
> +     gnttab_set_map_op(&op, (unsigned long)rxs,
>                         GNTMAP_host_map, rx_ring_ref, vif->domid);
>  
>       if (HYPERVISOR_grant_table_op(GNTTABOP_map_grant_ref, &op, 1))
> @@ -1656,7 +1663,6 @@ int xen_netbk_map_frontend_rings(struct xenvif *vif,
>       vif->rx_shmem_handle  = op.handle;
>       vif->rx_req_cons_peek = 0;
>  
> -     rxs = (struct xen_netif_rx_sring *)vif->rx_comms_area->addr;
>       BACK_RING_INIT(&vif->rx, rxs, PAGE_SIZE);
>  
>       return 0;



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