Since Xen-4.2, hvm domains may have portions of their memory paged out. When a
foreign domain (such as dom0) attempts to map these frames, the map will
initially fail. The hypervisor returns a suitable errno, and kicks an
asynchronous page-in operation carried out by a helper. The foreign domain is
expected to retry the mapping operation until it eventually succeeds. The
foreign domain is not put to sleep because itself could be the one running the
pager assist (typical scenario for dom0).

This patch adds support for this mechanism for backend drivers using grant
mapping and copying operations. Specifically, this covers the blkback and
gntdev drivers (which map foreign grants), and the netback driver (which copies
foreign grants).

* Add a retry method for grants that fail with GNTST_eagain (i.e. because the
  target foreign frame is paged out).
* Insert hooks with appropriate wrappers in the aforementioned drivers.

The retry loop is only invoked if the grant operation status is GNTST_eagain.
It guarantees to leave a new status code different from GNTST_eagain. Any other
status code results in identical code execution as before.

The retry loop performs 256 attempts with increasing time intervals through a
32 second period. It uses msleep to yield while waiting for the next retry.

V2 after feedback from David Vrabel:
* Explicit MAX_DELAY instead of wrap-around delay into zero
* Abstract GNTST_eagain check into core grant table code for netback module.

V3 after feedback from Ian Campbell:
* Add placeholder in array of grant table error descriptions for unrelated
  error code we jump over.
* Eliminate single map and retry macro in favor of a generic batch flavor.
* Some renaming.
* Bury most implementation in grant_table.c, cleaner interface.

V4 rebased on top of sync of Xen grant table interface headers.
Signed-off-by: NAndres Lagar-Cavilla <andres@lagarcavilla.org>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
[v5: Fixed whitespace issues]
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

After SKB is queued into tx_queue, it will be freed if request_gop is NULL.
However, no dequeue action is called in this situation, it is likely that
tx_queue constains freed SKB. This patch should fix this issue, and it is
based on 3.5.0-rc4+.

This issue is found through code inspection, no bug is seen with it currently.
I run netperf test for several hours, and no network regression was found.
Signed-off-by: NAnnie Li <annie.li@oracle.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

When calculating the number of slots required for a packet header, the code
was reserving too many slots if the header crossed a page boundary. Since
netbk_gop_skb copies the header to the start of the page, the count of
slots required for the header should be based solely on the header size.

This problem is easy to reproduce if a VIF is bridged to a USB 3G modem
device as the skb->data value always starts near the end of the first page.
Signed-off-by: NSimon Graham <simon.graham@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

alloc failures use dump_stack so emitting an additional
out-of-memory message is an unnecessary duplication.

Remove the allocation failure messages.
Signed-off-by: NJoe Perches <joe@perches.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Acked-by: NIan Campbell <ian.campbell@citrix.com>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NDaniel De Graaf <dgdegra@tycho.nsa.gov>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

"variables a used" should be "variables are used".
Signed-off-by: NWei Liu <wei.liu2@citrix.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

New value for netbk->mmap_pages[pending_idx] is assigned in
xen_netbk_alloc_page(), no need for a second assignment which
exposes internal to the outside world.
Signed-off-by: NWei Liu <wei.liu2@citrix.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The original message in netback_init was 'kthread_run() fails', which should be
'kthread_create() fails'.
Signed-off-by: NWei Liu <wei.liu2@citrix.com>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Signed-off-by: NJan Beulich <jbeulich@suse.com>
Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
Cc: stable@vger.kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

The xenbus module provides xenbus_map_ring_valloc() and
xenbus_map_ring_vfree().  Use these to map the Tx and Rx ring pages
granted by the frontend.
Signed-off-by: NDavid Vrabel <david.vrabel@citrix.com>
Acked-by: NDavid S. Miller <davem@davemloft.net>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

To ease skb->truesize sanitization, its better to be able to localize
all references to skb frags size.

Define accessors : skb_frag_size() to fetch frag size, and
skb_frag_size_{set|add|sub}() to manipulate it.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

netback currently uses frag->page to store a temporary index reference while
processing incoming requests. Since frag->page is to become opaque switch
instead to using page_offset. Add a wrapper to tidy this up and propagate the
fact that the indexes are only u16 through the code (this was already true in
practice but unsigned long and in were inconsistently used as variable and
parameter types)
Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
Cc: Ian Campbell <ian.campbell@citrix.com>
Cc: xen-devel@lists.xensource.com
Cc: netdev@vger.kernel.org
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Add xen-backend:vif module alias to the xen-netback module. This allows
automatic loading of the module.
Signed-off-by: NBastian Blank <waldi@debian.org>
Acked-by: NIan Campbell <ian.campbell@citrix.com>
Acked-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

netback is the host side counterpart to the frontend driver in
drivers/net/xen-netfront.c. The PV protocol is also implemented by
frontend drivers in other OSes too, such as the BSDs and even Windows.

The patch is based on the driver from the xen.git pvops kernel tree but
has been put through the checkpatch.pl wringer plus several manual
cleanup passes and review iterations. The driver has been moved from
drivers/xen/netback to drivers/net/xen-netback.

One major change from xen.git is that the guest transmit path (i.e. what
looks like receive to netback) has been significantly reworked to remove
the dependency on the out of tree PageForeign page flag (a core kernel
patch which enables a per page destructor callback on the final
put_page). This page flag was used in order to implement a grant map
based transmit path (where guest pages are mapped directly into SKB
frags). Instead this version of netback uses grant copy operations into
regular memory belonging to the backend domain. Reinstating the grant
map functionality is something which I would like to revisit in the
future.

Note that this driver depends on 2e820f58 "xen/irq: implement
bind_interdomain_evtchn_to_irqhandler for backend drivers" which is in
linux next via the "xen-two" tree and is intended for the 2.6.39 merge
window:
        git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen.git stable/backends
this branch has only that single commit since 2.6.38-rc2 and is safe for
cross merging into the net branch.
Signed-off-by: NIan Campbell <ian.campbell@citrix.com>
Reviewed-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>