Initial code for xen save/restore/migrate facilities.

- split the attach code of frontends in two half: one that is only needed
during autoconf(9) attach/detach phases, and one used at each save/restore
of device state (between suspend and resume).

Applies to hypervisor, xencons, xenbus, xbd, and xennet.

- add a rwlock(9) ("ptom_lock") to protect the different parts in the kernel
 that manipulate MFNs (which could change between a suspend and a resume,
without the kernel noticing it). Parts that require MFNs acquire a reader lock,
while suspend code will acquire a writer lock to ensure that no-other parts
in kernel still use MFNs.

- integrate the suspend code with sysmon.

- various things in pmap(9), and clock.

TODO:
- factorize code a bit more inside frontends drivers.
- remove all alternative recursive (APDP_PDE) mappings found in PD/PT during
suspend, as Xen does not support them.
- abstract the ptom_lock locking, it is only required when kernel preemption
is enabled, or on MP systems.

Current code works mostly. You may experience difficulties in some corner
cases (dom0 warnings about xennet interface errors, and Xen tools failing to
 validate NetBSD's alternative pmaps).
Sync with HEAD.

Commit is split, to avoid a "too many arguments" protocol error.
Sync with HEAD.

Second commit. See http://mail-index.netbsd.org/source-changes/2009/05/13/msg221222.html
Sync with HEAD.

Third (and last) commit. See http://mail-index.netbsd.org/source-changes/2009/05/13/msg221222.html
Fix a merge botch that hampered kernel's build for amd64.

Reported by cegger@ in private mail. Thanks.
- use uvm_km_alloc() instead of kmem_alloc() to enforce alignement when
allocating p2m_frame pages (xentools can only deal with page-aligned addresses)
- *sigh* do not use paddr_t for p2m_frame_list_list with PAE, xentools expect
32 bits addresses even with 64 bits PTE...
Sync with HEAD.
Modifications for the Xen suspend/migrate/resume branch:

- introduce xenbus_device_{suspend,resume}() functions. These are routines
used to suspend/resume MI parts of the Xenbus device interfaces, like updating
frontend/backend devices' paths found in XenStore.

- introduce HYPERVISOR_sysctl(), an hypercall used only by Xentools to obtain
information from hypervisor (listing VMs, printing console, etc.). I use it
to query xenconsole from ddb(), as a last resort in case of a panic() in
dom0 (xm being not available). Currently unused in the branch; could be, if
requested.

- disable the rwlock(9) used to protect code that could use transient MFNs.
It could trigger nasty context switches in place it should not to.

- fix some bugs in the xennet/xbd suspend/resume pmf(9) handlers.

- following XenSource's design, talk_to_otherend() is now called
watch_otherend(), and free_otherend_details() is used by Xenbus device
suspend/resume routines.

- some slight modifications in pmap regarding APDP. Introduce an inline
function (pmap_unmap_apdp_pde()) that clears APDP entry for the current pmap.

- similarly, implement pmap_unmap_all_apdp_pdes() that iterates through all
pmaps and tears down APDP, as Xen does not handle them properly.

TODO/XXX:

- pmap_unmap_apdp_pde() does not handle APDP shadow entry of PAE. It will,
once I figure out how PAE uses it.

- revisit the pmap locking issue regarding transient MFNs. As NetBSD does not
use kernel preemption and MP for Xen, this could be skipped momentarily. See
http://mail-index.netbsd.org/port-xen/2009/04/27/msg004903.html for details.

- fix a bug regarding grant tables which could technically DoS a dom0 if
ridiculously high consumer/producer indexes are passed down in the ring during
a resume.

All in all, once the grant table index issue and APDP PAE are fixed, next step
is to torture test this branch.

Tested under i386 PAE and non-PAE, Xen3 dom0 and domU. amd64 is only compile
tested.
As requested by cegger@, apply the following patch to jym-xensuspend branch:

Interrupt handling in Xen 3.5 changed. There's no longer
a hardcoded upper limit. So *our* upper limit of 200 may be different from machine to machine now.
So just retry if the hypercall failed.
register physical CPUs with pmf.
No suspend/resume handlers needed since the hypervisor itself handles them.
ok @jym
implement ACPI S3 support for Dom0.
ok jym@
Sync with HEAD.
- rework the page pinning API, so that now a function is provided for
each level of indirection encountered during virtual memory translations. Update
pmap accordingly. Pinning looks cleaner that way, and it offers the possibility
to pin lower level pages if necessary (NetBSD does not do it currently).

- some fixes and comments to explain how page validation/invalidation take
place during save/restore/migrate under Xen. L2 shadow entries from PAE are now
handled, so basically, suspend/resume works with PAE.

- fixes an issue reported by Christoph (cegger@) for xencons suspend/resume
in dom0.

TODO:

- PAE save/restore is currently limited to single-user only, multi-user
support requires modifications in PAE pmap that should be discussed first. See
the comments about the L2 shadow pages cached in pmap_pdp_cache in this commit.

- grant table bug is still there; do not use the kernels of this branch
to test suspend/resume, unless you want to experience bad crashes in dom0,
and push the big red button.

Now there is light at the end of the tunnel :)

Note: XEN2 kernels will neither build nor work with this branch.
Sync with HEAD.
- Upgrade suspend/resume code to comply with Xen2 removal.
- Add support for PAE domUs suspend/resume.
- Fix an issue regarding initialization of the xbd ring I/O that could end
badly during resume, with invalid block operations submitted to dom0 backend.

NetBSD supports PAE under x86_32 by considering the L2 page as being
4 pages long instead of 1.

Xen validates the page types during resume. Sadly, the hypervisor handles
alternative recursive mappings (== PG/PD entries pointing to pages other
than self) inadequately, which could lead to incorrect page pinning.

As a result, the important change with this patch is to clear these alternative
mappings during suspend, and reset them back to their former self upon
resume. For PAE, approx. all 4 PDIR_SLOT_PTEs could be considered as
alternative recursive mappings.

See comments in pmap.c for further details.

Now, let the testing and bug hunting begin.
Sync with HEAD
Sync with HEAD
Sync with HEAD. TODO before merge:
- shortcut for suspend code in sysmon, when powerd(8) is not running.
Borrow ``xs_watch'' thread context?
- bug hunting in xbd + xennet resume. Rings are currently thrashed upon
resume, so current implementation force flush them on suspend. It's not
really needed.
Cure sync hiccups. Code with compile errors is not really useful, heh.
More sync fixes. And add the mbr_gpt files.