Right now all RCU walks fall back to reference walk when CONFIG_SECURITY
is enabled, even though just the standard capability module is active.
This is because security_inode_exec_permission unconditionally fails
RCU walks.

Move this decision to the low level security module. This requires
passing the RCU flags down the security hook. This way at least
the capability module and a few easy cases in selinux/smack work
with RCU walks with CONFIG_SECURITY=y
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NEric Paris <eparis@redhat.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6:
  ALSA: hda - Fix unused warnings when !SND_HDA_NEEDS_RESUME
  ALSA: hda - Add a fix-up for Acer dmic with ALC271x codec
  ASoC: add a module alias to the FSI driver
  ALSA: emu10k1 - Fix "Music" controls to "Synth" controls in documents
  ARM: s3c2440: gta02; Register dfbmcs320 device for BT audio interface
  ASoC: codecs: JZ4740: Fix OOPS
  ASoC: Fix output PGA enabling in wm_hubs CODECs
  ASoC: sn95031: decorate function with __devexit_p()
  ASoC: SAMSUNG: Fix the inverted clocks handling for pcm driver
  ASoC: sst_platform: Fix lock acquring
  ASoC: fsi: driver safely remove for against irq
  ASoC: fsi: modify vague PM control on probe
  ASoC: fsi: take care in failing case of dai register
  MAINTAINERS: Update Samsung ASoC maintainer's id
  ASoC: WM8903: HP and Line out PGA/mixer DAPM fixes
  ASoC: Set left channel volume update bits for WM8994
  ASoC: fix config error path
  ASoC: check channel mismatch between cpu_dai and codec_dai
  ASoC: Tegra: Suspend/resume support

Merge branch 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'perf-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  perf, x86: Update/fix Intel Nehalem cache events
  perf, x86: P4 PMU - Don't forget to clear cpuc->active_mask on overflow
  x86, perf event: Turn off unstructured raw event access to offcore registers
  perf: Support Xeon E7's via the Westmere PMU driver

Merge branch 'irq-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'irq-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  xtensa: Fixup irq conversion fallout and nmi_count

Change the Nehalem cache events to use retired memory instruction counters
(similar to Westmere), this greatly improves the provided stats.

Using:

main ()
{
        int i;

        for (i = 0; i < 1000000000; i++) {
                asm("mov (%%rsp), %%rbx;"
                    "mov %%rbx, (%%rsp);" : : : "rbx");
        }
}

We find:

 $ perf stat --repeat 10 -e instructions:u -e l1-dcache-loads:u -e l1-dcache-stores:u ./loop_1b_loads+stores
  Performance counter stats for './loop_1b_loads+stores' (10 runs):
      4,000,081,056 instructions:u           #      0.000 IPC ( +-   0.000% )
      4,999,502,846 l1-dcache-loads:u          ( +-   0.008% )
      1,000,034,832 l1-dcache-stores:u         ( +-   0.000% )
         1.565184942  seconds time elapsed   ( +-   0.005% )

The 5b is surprising - we'd expect 1b:

 $ perf stat --repeat 10 -e instructions:u -e r10b:u -e l1-dcache-stores:u ./loop_1b_loads+stores
  Performance counter stats for './loop_1b_loads+stores' (10 runs):
      4,000,081,054 instructions:u           #      0.000 IPC ( +-   0.000% )
      1,000,021,961 r10b:u                     ( +-   0.000% )
      1,000,030,951 l1-dcache-stores:u         ( +-   0.000% )
         1.565055422  seconds time elapsed   ( +-   0.003% )

Which this patch thus fixes.
Signed-off-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Lin Ming <ming.m.lin@intel.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Link: http://lkml.kernel.org/n/tip-q9rtru7b7840tws75xzboapv@git.kernel.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>

It's not enough to simply disable event on overflow the
cpuc->active_mask should be cleared as well otherwise counter
may stall in "active" even in real being already disabled (which
potentially may lead to the situation that user may not use this
counter further).

Don pointed out that:

 " I also noticed this patch fixed some unknown NMIs
   on a P4 when I stressed the box".
Tested-by: NLin Ming <ming.m.lin@intel.com>
Signed-off-by: NCyrill Gorcunov <gorcunov@openvz.org>
Acked-by: NDon Zickus <dzickus@redhat.com>
Signed-off-by: NDon Zickus <dzickus@redhat.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Link: http://lkml.kernel.org/r/1303398203-2918-3-git-send-email-dzickus@redhat.comSigned-off-by: NIngo Molnar <mingo@elte.hu>

Andi Kleen pointed out that the Intel offcore support patches were merged
without user-space tool support to the functionality:

 |
 | The offcore_msr perf kernel code was merged into 2.6.39-rc*, but the
 | user space bits were not. This made it impossible to set the extra mask
 | and actually do the OFFCORE profiling
 |

Andi submitted a preliminary patch for user-space support, as an
extension to perf's raw event syntax:

 |
 | Some raw events -- like the Intel OFFCORE events -- support additional
 | parameters. These can be appended after a ':'.
 |
 | For example on a multi socket Intel Nehalem:
 |
 |    perf stat -e r1b7:20ff -a sleep 1
 |
 | Profile the OFFCORE_RESPONSE.ANY_REQUEST with event mask REMOTE_DRAM_0
 | that measures any access to DRAM on another socket.
 |

But this kind of usability is absolutely unacceptable - users should not
be expected to type in magic, CPU and model specific incantations to get
access to useful hardware functionality.

The proper solution is to expose useful offcore functionality via
generalized events - that way users do not have to care which specific
CPU model they are using, they can use the conceptual event and not some
model specific quirky hexa number.

We already have such generalization in place for CPU cache events,
and it's all very extensible.

"Offcore" events measure general DRAM access patters along various
parameters. They are particularly useful in NUMA systems.

We want to support them via generalized DRAM events: either as the
fourth level of cache (after the last-level cache), or as a separate
generalization category.

That way user-space support would be very obvious, memory access
profiling could be done via self-explanatory commands like:

  perf record -e dram ./myapp
  perf record -e dram-remote ./myapp

... to measure DRAM accesses or more expensive cross-node NUMA DRAM
accesses.

These generalized events would work on all CPUs and architectures that
have comparable PMU features.

( Note, these are just examples: actual implementation could have more
  sophistication and more parameter - as long as they center around
  similarly simple usecases. )

Now we do not want to revert *all* of the current offcore bits, as they
are still somewhat useful for generic last-level-cache events, implemented
in this commit:

  e994d7d2: perf: Fix LLC-* events on Intel Nehalem/Westmere

But we definitely do not yet want to expose the unstructured raw events
to user-space, until better generalization and usability is implemented
for these hardware event features.

( Note: after generalization has been implemented raw offcore events can be
  supported as well: there can always be an odd event that is marginally
  useful but not useful enough to generalize. DRAM profiling is definitely
  *not* such a category so generalization must be done first. )

Furthermore, PERF_TYPE_RAW access to these registers was not intended
to go upstream without proper support - it was a side-effect of the above
e994d7d2 commit, not mentioned in the changelog.

As v2.6.39 is nearing release we go for the simplest approach: disable
the PERF_TYPE_RAW offcore hack for now, before it escapes into a released
kernel and becomes an ABI.

Once proper structure is implemented for these hardware events and users
are offered usable solutions we can revisit this issue.
Reported-by: NAndi Kleen <ak@linux.intel.com>
Acked-by: NPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1302658203-4239-1-git-send-email-andi@firstfloor.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>

There's a new model number public, 47, for Xeon E7 (aka Westmere EX).
Signed-off-by: NAndi Kleen <ak@linux.intel.com>
Cc: a.p.zijlstra@chello.nl
Link: http://lkml.kernel.org/r/1303429715-10202-1-git-send-email-andi@firstfloor.orgSigned-off-by: NIngo Molnar <mingo@elte.hu>

* 'for-linus' of git://git.kernel.dk/linux-2.6-block:
  ide: unexport DISK_EVENT_MEDIA_CHANGE for ide-gd and ide-cd
  block: don't propagate unlisted DISK_EVENTs to userland
  elevator: check for ELEVATOR_INSERT_SORT_MERGE in !elvpriv case too

check_events() implementations in both ide-gd and ide-cd are
inadequate for in-kernel event polling.  Both generate media change
events continuously when certain conditions are met causing infinite
event loop between the driver and userland event handler.

As disk event now supports suppression of unlisted events, simply
de-listing DISK_EVENT_MEDIA_CHANGE from disk->events resolves the
problem.  Internal handling around media revalidation will behave the
same while userland will fall back to userland event polling after
detecting the device doesn't support disk events.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-by: NJens Axboe <jaxboe@fusionio.com>
Acked-by: N"David S. Miller" <davem@davemloft.net>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

DISK_EVENT_MEDIA_CHANGE is used for both userland visible event and
internal event for revalidation of removeable devices.  Some legacy
drivers don't implement proper event detection and continuously
generate events under certain circumstances.  For example, ide-cd
generates media changed continuously if there's no media in the drive,
which can lead to infinite loop of events jumping back and forth
between the driver and userland event handler.

This patch updates disk event infrastructure such that it never
propagates events not listed in disk->events to userland.  Those
events are processed the same for internal purposes but uevent
generation is suppressed.

This also ensures that userland only gets events which are advertised
in the @events sysfs node lowering risk of confusion.
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

The sort insert is the one that goes to the IO scheduler. With
the SORT_MERGE addition, we could bypass IO scheduler setup
but still ask the IO scheduler to insert the request. This would
cause an oops on switching IO schedulers through the sysfs
interface, unless the disk just happened to be idle while it
occured.
Signed-off-by: NJens Axboe <jaxboe@fusionio.com>

* 'for-linus' of git://oss.sgi.com/xfs/xfs:
  xfs: fix duplicate message output

Merge branch 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'x86-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  x86, numa: Fix cpu nodemasks for NUMA emulation and CONFIG_DEBUG_PER_CPU_MAPS
  Revert "x86, NUMA: Fix fakenuma boot failure"

Change <sectors> from unsigned long long to sector_t.
This matches its source field.

  ERROR: "__udivdi3" [drivers/md/raid456.ko] undefined!
Signed-off-by: NRandy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

* git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux-2.6-for-linus:
  virtio: console: Enable call to hvc_remove() on console port remove
  virtio_pci: Prevent double-free of pci regions after device hot-unplug
  virtio: Decrement avail idx on buffer detach

* 'drm-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/airlied/drm-2.6:
  agp: fix arbitrary kernel memory writes
  agp: fix OOM and buffer overflow
  drm/radeon/kms: fix IH writeback on r6xx+ on big endian machines

* 'drm-intel-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/keithp/linux-2.6:
  drm/i915: Initialise g4x watermarks for disabled pipes
  drm/i915: Sanitize the output registers after resume
  drm/i915/tv: Fix modeset flickering introduced in 7f58aabc
  drm/i915/tv: Only poll for TV connections
  drm/i915/tv: Remember the detected TV type

* git://git.infradead.org/iommu-2.6:
  intel_iommu: disable all VT-d PMRs when TXT launched
  intel-iommu: Fix get_domain_for_dev() error path
  intel-iommu: Unlink domain from iommu
  intel-iommu: Fix use after release during device attach

For some reason generic_setxattr() did not pass flags (XATTR_CREATE,
XATTR_REPLACE) to the filesystem specific helper. This caused that
setxattr(2) syscall just ignored these flags.

Fix the bug by passing flags correctly.
Signed-off-by: NJan Kara <jack@suse.cz>
Acked-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This call was disabled as hot-unplugging one virtconsole port led to
another virtconsole port freezing.

Upon testing it again, this now works, so enable it.

In addition, a bug was found in qemu wherein removing a port of one type
caused the guest output from another port to stop working.  I doubt it
was just this bug that caused it (since disabling the hvc_remove() call
did allow other ports to continue working), but since it's all solved
now, we're fine with hot-unplugging of virtconsole ports.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

In the case where a virtio-console port is in use (opened by a program)
and a virtio-console device is removed, the port is kept around but all
the virtio-related state is assumed to be gone.

When the port is finally released (close() called), we call
device_destroy() on the port's device.  This results in the parent
device's structures to be freed as well.  This includes the PCI regions
for the virtio-console PCI device.

Once this is done, however, virtio_pci_release_dev() kicks in, as the
last ref to the virtio device is now gone, and attempts to do

     pci_iounmap(pci_dev, vp_dev->ioaddr);
     pci_release_regions(pci_dev);
     pci_disable_device(pci_dev);

which results in a double-free warning.

Move the code that releases regions, etc., to the virtio_pci_remove()
function, and all that's now left in release_dev is the final freeing of
the vp_dev.
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

When detaching a buffer from a vq, the avail.idx value should be
decremented as well.

This was noticed by hot-unplugging a virtio console port and then
plugging in a new one on the same number (re-using the vqs which were
just 'disowned').  qemu reported

   'Guest moved used index from 0 to 256'

when any IO was attempted on the new port.

CC: stable@kernel.org
Reported-by: Njuzhang <juzhang@redhat.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

Intel VT-d Protected Memory Regions (PMRs) are supposed to be disabled,
on each VT-d engine, after DMA remapping is enabled on the engines.
This is because the behavior of having both enabled is not deterministic
and because, if TXT has been used to launch the kernel, the PMRs may be
programmed to cover memory regions that will be used for DMA.

Under some circumstances (certain quirks detected, lack of multiple
devices, etc.), the current code does not set up DMA remapping on some
VT-d engines.  In such cases it also skips disabling the PMRs.  This
causes failures when the kernel is launched with TXT (most often this
occurs on the graphics engine and results in colored vertical bars on
the display).

This patch detects when the kernel has been launched with TXT and then
disables the PMRs on all VT-d engines.  In some cases where the reason
that remapping is not being enabled is due to possible ACPI DMAR table
errors, the VT-d engine addresses may not be correct and thus not able
to be safely programmed even to disable PMRs.  Because part of the TXT
launch process is the verification of these addresses, it will always be
safe to disable PMRs if the TXT launch has succeeded and hence only
doing this in such cases.
Signed-off-by: NJoseph Cihula <joseph.cihula@intel.com>
Signed-off-by: NDavid Woodhouse <David.Woodhouse@intel.com>

The cpu<->node mappings under CONFIG_DEBUG_PER_CPU_MAPS=y
when NUMA emulation is enabled is currently broken because it does
not iterate through every emulated node and bind cpus that have
affinity to it.

NUMA emulation should bind each cpu to every local node to
accurately represent the true NUMA topology of the underlying
machine.

debug_cpumask_set_cpu() needs to be fixed at the same time so
that the debugging information that it emits shows the new
cpumask of the node being assigned when the cpu is being added
or removed.

It can now take responsibility of setting or clearing the cpu
itself to remove the need for duplicate code.

Also change its last parameter, "enable", to have the correct bool
type since it can only be true or false.

 -v2: Fix the return statements, by Kosaki Motohiro
Acked-and-Tested-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: NDavid Rientjes <rientjes@google.com>
Cc: Andreas Herrmann <herrmann.der.user@googlemail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1104201918470.12634@chino.kir.corp.google.comSigned-off-by: NIngo Molnar <mingo@elte.hu>

Andreas Herrmann reported that 7d6b4670 ("x86, NUMA: Fix fakenuma
boot failure") causes certain physical NUMA topologies (for example
AMD Magny-Cours) to move sibling cpus to a single node when in reality
they are in separate domains.

This may result in some nodes being completely void of cpus, which
doesn't accurately represent the correct topology. The system will
boot, but will have suboptimal NUMA performance.

This commit was intended as a fix for NUMA emulation, but should
not cause a regression for real NUMA machines as a side effect.

( There will be a separate fix for the numa-debug code, which
  will not affect physical topologies. )
Reported-by: NAndreas Herrmann <herrmann.der.user@googlemail.com>
Signed-off-by: NDavid Rientjes <rientjes@google.com>
Acked-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/alpine.DEB.2.00.1104201918110.12634@chino.kir.corp.google.comSigned-off-by: NIngo Molnar <mingo@elte.hu>

pg_start is copied from userspace on AGPIOC_BIND and AGPIOC_UNBIND ioctl
cmds of agp_ioctl() and passed to agpioc_bind_wrap().  As said in the
comment, (pg_start + mem->page_count) may wrap in case of AGPIOC_BIND,
and it is not checked at all in case of AGPIOC_UNBIND.  As a result, user
with sufficient privileges (usually "video" group) may generate either
local DoS or privilege escalation.
Signed-off-by: NVasiliy Kulikov <segoon@openwall.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

page_count is copied from userspace.  agp_allocate_memory() tries to
check whether this number is too big, but doesn't take into account the
wrap case.  Also agp_create_user_memory() doesn't check whether
alloc_size is calculated from num_agp_pages variable without overflow.
This may lead to allocation of too small buffer with following buffer
overflow.

Another problem in agp code is not addressed in the patch - kernel memory
exhaustion (AGPIOC_RESERVE and AGPIOC_ALLOCATE ioctls).  It is not checked
whether requested pid is a pid of the caller (no check in agpioc_reserve_wrap()).
Each allocation is limited to 16KB, though, there is no per-process limit.
This might lead to OOM situation, which is not even solved in case of the
caller death by OOM killer - the memory is allocated for another (faked) process.
Signed-off-by: NVasiliy Kulikov <segoon@openwall.com>
Signed-off-by: NDave Airlie <airlied@redhat.com>

* 'hwmon-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/groeck/staging:
  hwmon: (max34440) Add driver documentation
  hwmon: (max16064) Add driver documentation
  hwmon: (max8688) Add driver documentation
  hwmon: (pmbus) Documentation updates
  hwmon: (smm665) Fix spelling error in driver documentation
  hwmon: (pmbus) Removed unused variable from struct pmbus_data
  hwmon: Add submitting-patches checklist to documentation

* 'for-2.6.39' of git://linux-nfs.org/~bfields/linux:
  Open with O_CREAT flag set fails to open existing files on non writable directories
  nfsd4: Fix filp leak
  nfsd4: fix struct file leak on delegation

* 'fixes' of master.kernel.org:/home/rmk/linux-2.6-arm:
  ARM: 6881/1: cputype.h uses __attribute_const__ which requires including kernel.h
  ARM: Add new syscalls

* 'stable/bug-fixes-rc4' of git://git.kernel.org/pub/scm/linux/kernel/git/konrad/xen:
  xen: mask_rw_pte: do not apply the early_ioremap checks on x86_32
  xen: do not create the extra e820 region at an addr lower than 4G

* 'for-linus' of git://neil.brown.name/md:
  md: Update documentation for sync_min and sync_max entries
  md: Cleanup after raid45->raid0 takeover
  md: Fix dev_sectors on takeover from raid0 to raid4/5
  md/raid5: remove setting of ->queue_lock

When SND_HDA_NEEDS_RESUME is not defined, the compiler identifies that
the following symbols are static but not used:

 restore_shutup_pins
 hda_cleanup_all_streams

Fix warnings by adding SND_HDA_NEEDS_RESUME guards.
Signed-off-by: NMike Waychison <mikew@google.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

* 'for-linus' of git://git.kernel.dk/linux-2.6-block:
  block: Remove the extra check in queue_requests_store
  block, blk-sysfs: Fix an err return path in blk_register_queue()
  block: remove stale kerneldoc member from __blk_run_queue()
  block: get rid of QUEUE_FLAG_REENTER
  cfq-iosched: read_lock() does not always imply rcu_read_lock()
  block: kill blk_flush_plug_list() export

Commit 957935dc ("xfs: fix xfs_debug warnings" broke the logic in
__xfs_printk(). Instead of only printing one of two possible output
strings based on whether the fs has a name or not, it outputs both.
Fix it to only output one message again.
Signed-off-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAlex Elder <aelder@sgi.com>

An open on a NFS4 share using the O_CREAT flag on an existing file for
which we have permissions to open but contained in a directory with no
write permissions will fail with EACCES.

A tcpdump shows that the client had set the open mode to UNCHECKED which
indicates that the file should be created if it doesn't exist and
encountering an existing flag is not an error. Since in this case the
file exists and can be opened by the user, the NFS server is wrong in
attempting to check create permissions on the parent directory.

The patch adds a conditional statement to check for create permissions
only if the file doesn't exist.
Signed-off-by: NSachin S. Prabhu <sprabhu@redhat.com>
Signed-off-by: NJ. Bruce Fields <bfields@redhat.com>

The two "is_early_ioremap_ptep" checks in mask_rw_pte are only used on
x86_64, in fact early_ioremap is not used at all to setup the initial
pagetable on x86_32.
Moreover on x86_32 the two checks are wrong because the range
pgt_buf_start..pgt_buf_end initially should be mapped RW because
the pages in the range are not pagetable pages yet and haven't been
cleared yet. Afterwards considering the pgt_buf_start..pgt_buf_end is
part of the initial mapping, xen_alloc_pte is capable of turning
the ptes RO when they become pagetable pages.

Fix the issue and improve the readability of the code providing two
different implementation of mask_rw_pte for x86_32 and x86_64.
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Do not add the extra e820 region at a physical address lower than 4G
because it breaks e820_end_of_low_ram_pfn().

It is OK for us to move the xen_extra_mem_start up and down because this
is the index of the memory that can be ballooned in/out - it is memory
not available to the kernel during bootup.
Signed-off-by: NStefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: NKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>