The PV block protocol is using 4KB page granularity. The goal of this
patch is to allow a Linux using 64KB page granularity using block
device on a non-modified Xen.

The block API is using segment which should at least be the size of a
Linux page. Therefore, the driver will have to break the page in chunk
of 4K before giving the page to the backend.

When breaking a 64KB segment in 4KB chunks, it is possible that some
chunks are empty. As the PV protocol always require to have data in the
chunk, we have to count the number of Xen page which will be in use and
avoid sending empty chunks.

Note that, a pre-defined number of grants are reserved before preparing
the request. This pre-defined number is based on the number and the
maximum size of the segments. If each segment contains a very small
amount of data, the driver may reserve too many grants (16 grants is
reserved per segment with 64KB page granularity).

Furthermore, in the case of persistent grants we allocate one Linux page
per grant although only the first 4KB of the page will be effectively
in use. This could be improved by sharing the page with multiple grants.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

The Xen interface is using 4KB page granularity. This means that each
grant is 4KB.

The current implementation allocates a Linux page per grant. On Linux
using 64KB page granularity, only the first 4KB of the page will be
used.

We could decrease the memory wasted by sharing the page with multiple
grant. It will require some care with the {Set,Clear}ForeignPage macro.

Note that no changes has been made in the x86 code because both Linux
and Xen will only use 4KB page granularity.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Only use the first 4KB of the page to store the events channel info. It
means that we will waste 60KB every time we allocate page for:
     * control block: a page is allocating per CPU
     * event array: a page is allocating everytime we need to expand it

I think we can reduce the memory waste for the 2 areas by:

    * control block: sharing between multiple vCPUs. Although it will
    require some bookkeeping in order to not free the page when the CPU
    goes offline and the other CPUs sharing the page still there

    * event array: always extend the array event by 64K (i.e 16 4K
    chunk). That would require more care when we fail to expand the
    event channel.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

For ARM64 guests, Linux is able to support either 64K or 4K page
granularity. Although, the hypercall interface is always based on 4K
page granularity.

With 64K page granularity, a single page will be spread over multiple
Xen frame.

To avoid splitting the page into 4K frame, take advantage of the
extent_order field to directly allocate/free chunk of the Linux page
size.

Note that PVMMU is only used for PV guest (which is x86) and the page
granularity is always 4KB. Some BUILD_BUG_ON has been added to ensure
that because the code has not been modified.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

The console ring is always based on the page granularity of Xen.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

All the ring (xenstore, and PV rings) are always based on the page
granularity of Xen.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

On ARM all dma-capable devices on a same platform may not be protected
by an IOMMU. The DMA requests have to use the BFN (i.e MFN on ARM) in
order to use correctly the device.

While the DOM0 memory is allocated in a 1:1 fashion (PFN == MFN), grant
mapping will screw this contiguous mapping.

When Linux is using 64KB page granularitary, the page may be split
accross multiple non-contiguous MFN (Xen is using 4KB page
granularity). Therefore a DMA request will likely fail.

Checking that a 64KB page is using contiguous MFN is tedious. For
now, always says that biovec are not mergeable.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Prepare the code to support 64KB page granularity. The first
implementation will use a full Linux page per indirect and persistent
grant. When non-persistent grant is used, each page of a bio request
may be split in multiple grant.

Furthermore, the field page of the grant structure is only used to copy
data from persistent grant or indirect grant. Avoid to set it for other
use case as it will have no meaning given the page will be split in
multiple grant.

Provide 2 functions, to setup indirect grant, the other for bio page.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

All the usage of the field pfn are done using the same idiom:

pfn_to_page(grant->pfn)

This will  return always the same page. Store directly the page in the
grant to clean up the code.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Currently, blkif_queue_request has 2 distinct execution path:
    - Send a discard request
    - Send a read/write request

The function is also allocating grants to use for generating the
request. Although, this is only used for read/write request.

Rather than having a function with 2 distinct execution path, separate
the function in 2. This will also remove one level of tabulation.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Many PV drivers contain the idiom:

pfn = page_to_gfn(...) /* Or similar */
gnttab_grant_foreign_access_ref

Replace it by a new helper. Note that when Linux is using a different
page granularity than Xen, the helper only gives access to the first 4KB
grant.

This is useful where drivers are allocating a full Linux page for each
grant.

Also include xen/interface/grant_table.h rather than xen/grant_table.h in
asm/page.h for x86 to fix a compilation issue [1]. Only the former is
useful in order to get the structure definition.

[1] Interdependency between asm/page.h and xen/grant_table.h which result
to page_mfn not being defined when necessary.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Currently, a grant is always based on the Xen page granularity (i.e
4KB). When Linux is using a different page granularity, a single page
will be split between multiple grants.

The new helpers will be in charge of splitting the Linux page into grants
and call a function given by the caller on each grant.

Also provide an helper to count the number of grants within a given
contiguous region.

Note that the x86/include/asm/xen/page.h is now including
xen/interface/grant_table.h rather than xen/grant_table.h. It's
necessary because xen/grant_table.h depends on asm/xen/page.h and will
break the compilation. Furthermore, only definition in
interface/grant_table.h is required.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

The Xen hypercall interface is always using 4K page granularity on ARM
and x86 architecture.

With the incoming support of 64K page granularity for ARM64 guest, it
won't be possible to re-use the Linux page definition in Xen drivers.

Introduce Xen page definition helpers based on the Linux page
definition. They have exactly the same name but prefixed with
XEN_/xen_ prefix.

Also modify xen_page_to_gfn to use new Xen page definition.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

They are not used in common code expect in one place in balloon.c which is
only compiled when Linux is using PV MMU. It's not the case on ARM.

Rather than worrying how to handle the 64KB case, drop them.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Reviewed-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

The skb doesn't change within the function. Therefore it's only
necessary to check if we need GSO once at the beginning.
Signed-off-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>

Pages returned by alloc_xenballooned_pages() will be used for grant
mapping which will call set_phys_to_machine() (in PV guests).

Ballooned pages are set as INVALID_P2M_ENTRY in the p2m and thus may
be using the (shared) missing tables and a subsequent
set_phys_to_machine() will need to allocate new tables.

Since the grant mapping may be done from a context that cannot sleep,
the p2m entries must already be allocated.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Rename alloc_p2m() to xen_alloc_p2m_entry() and export it.

This is useful for ensuring that a p2m entry is allocated (i.e., not a
shared missing or identity entry) so that subsequent set_phys_to_machine()
calls will require no further allocations.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
v3:
- Make xen_alloc_p2m_entry() a nop on auto-xlate guests.

alloc_xenballooned_pages() is used to get ballooned pages to back
foreign mappings etc.  Instead of having to balloon out real pages,
use (if supported) hotplugged memory.

This makes more memory available to the guest and reduces
fragmentation in the p2m.

This is only enabled if the xen.balloon.hotplug_unpopulated sysctl is
set to 1.  This sysctl defaults to 0 in case the udev rules to
automatically online hotplugged memory do not exist.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
v3:
- Add xen.balloon.hotplug_unpopulated sysctl to enable use of hotplug
  for unpopulated pages.

All users of alloc_xenballoon_pages() wanted low memory pages, so
remove the option for high memory.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Now that we track the total number of pages (included hotplugged
regions), it is easy to determine if more memory needs to be
hotplugged.

Add a new BP_WAIT state to signal that the balloon process needs to
wait until kicked by the memory add notifier (when the new section is
onlined by userspace).
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
v3:
- Return BP_WAIT if enough sections are already hotplugged.

v2:
- New BP_WAIT status after adding new memory sections.

The stats used for memory hotplug make no sense and are fiddled with
in odd ways.  Remove them and introduce total_pages to track the total
number of pages (both populated and unpopulated) including those within
hotplugged regions (note that this includes not yet onlined pages).

This will be used in a subsequent commit (xen/balloon: only hotplug
additional memory if required) when deciding whether additional memory
needs to be hotplugged.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Instead of placing hotplugged memory at the end of RAM (which may
conflict with PCI devices or reserved regions) use allocate_resource()
to get a new, suitably aligned resource that does not conflict.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
v3:
- Remove stale comment.

During setup, discard RAM regions that are above the maximum
reservation (instead of marking them as E820_UNUSABLE).  This allows
hotplug memory to be placed at these addresses.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Commit 0bb599fd (xen: remove scratch
frames for ballooned pages and m2p override) removed the use of the
scratch page for ballooned out pages.

Remove some left over function definitions.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Add add_memory_resource() to add memory using an existing "System RAM"
resource.  This is useful if the memory region is being located by
finding a free resource slot with allocate_resource().

Xen guests will make use of this in their balloon driver to hotplug
arbitrary amounts of memory in response to toolstack requests.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Reviewed-by: Tang Chen <tangchen@cn.fujitsu.com>

Pull i2c fixes from Wolfram Sang:
 "Here are some bugfixes for the I2C subsystem.

  Kieran found a flaw in the recently renewed wake irq handling.  Mika
  handled a user bug report where the ACPI info turned out to be
  unusable.  I updated MAINTAINERS so that such bug reports will sooner
  get to the right people.  Geert pointed me to a problem of some i2c
  drivers regarding PM which I fixed"

* 'i2c/for-current' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux:
  i2c: designware: Do not use parameters from ACPI on Dell Inspiron 7348
  MAINTAINERS: add maintainers for Synopsis Designware I2C drivers
  i2c: designware-platdrv: enable RuntimePM before registering to the core
  i2c: s3c2410: enable RuntimePM before registering to the core
  i2c: rcar: enable RuntimePM before registering to the core
  i2c: return probe deferred status on dev_pm_domain_attach

ACPI SSCN/FMCN methods were originally added because then the platform can
provide the most accurate HCNT/LCNT values to the driver. However, this
seems not to be true for Dell Inspiron 7348 where using these causes the
touchpad to fail in boot:

  i2c_hid i2c-DLL0675:00: failed to retrieve report from device.
  i2c_designware INT3433:00: i2c_dw_handle_tx_abort: lost arbitration
  i2c_hid i2c-DLL0675:00: failed to retrieve report from device.
  i2c_designware INT3433:00: controller timed out

The values received from ACPI are (in fast mode):

  HCNT: 72
  LCNT: 160

this translates to following timings (input clock is 100MHz on Broadwell):

  tHIGH: 720 ns (spec min 600 ns)
  tLOW: 1600 ns (spec min 1300 ns)
  Bus period: 2920 ns (assuming 300 ns tf and tr)
  Bus speed: 342.5 kHz

Both tHIGH and tLOW are within the I2C specification.

The calculated values when ACPI parameters are not used are (in fast mode):

  HCNT: 87
  LCNT: 159

which translates to:

  tHIGH: 870 ns (spec min 600 ns)
  tLOW: 1590 ns (spec min 1300 ns)
  Bus period 3060 ns (assuming 300 ns tf and tr)
  Bus speed 326.8 kHz

These values are also within the I2C specification.

Since both ACPI and calculated values meet the I2C specification timing
requirements it is hard to say why the touchpad does not function properly
with the ACPI values except that the bus speed is higher in this case (but
still well below the max 400kHz).

Solve this by adding DMI quirk to the driver that disables using ACPI
parameters on this particulare machine.
Reported-by: Pavel Roskin <plroskin@gmail.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Tested-by: Pavel Roskin <plroskin@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: stable@kernel.org

Merge branches 'irq-urgent-for-linus' and 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull irq/timer fixes from Thomas Gleixner:
 "irq: a fix for the new hierarchical MSI interrupt handling which
  unbreaks PCI=n configurations.

  timers: a fix for the new hrtimer clock offset update mechanism to
  ensure that the boot time offset is respected"

* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  genirq/msi: Do not use pci_msi_[un]mask_irq as default methods

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timekeeping: Increment clock_was_set_seq in timekeeping_init()

Pull input fixes from Dmitry Torokhov:
 "Just two small fixups to ads7846 touchscreen controller driver and
  Cypress touchpad driver"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/dtor/input:
  Input: cyapa - fix the copy paste error on electrodes_rx value
  Input: ads7846 - correct the value got from SPI

Pull clk fix from Stephen Boyd:
 "Just one revert for Armada XP devices: the conversion to
  of_clk_get_parent_name() wasn't a direct translation, so we
  revert back to of_clk_get() + __clk_get_name().

  We could make of_clk_get_parent_name() more robust, but that
  may have unintended side-effects, so we'll do that in the
  next version"

* tag 'clk-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/clk/linux:
  Partially revert "clk: mvebu: Convert to clk_hw based provider APIs"

Pull device mapper fixes from Mike Snitzer:
 "Two DM target error path cleanup fixes (one for stable in DM thinp and
  one for a v4.3-rc5 thinko in DM snapshot)"

* tag 'dm-4.3-fixes-3' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm thin: fix missing pool reference count decrement in pool_ctr error path
  dm snapshot persistent: fix missing cleanup in persistent_ctr error path

Pull btrfs fixes from Chris Mason:
 "I have two more bug fixes for btrfs.

  My commit fixes a bug we hit last week at FB, a combination of lots of
  hard links and an admin command to resolve inode numbers.

  Dave is adding checks to make sure balance on current kernels ignores
  filters it doesn't understand.  The penalty for being wrong is just
  doing more work (not crashing etc), but it's a good fix"

* 'for-linus-4.3' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs:
  btrfs: fix use after free iterating extrefs
  btrfs: check unsupported filters in balance arguments

Pull Ceph fixes from Sage Weil:
 "Just two small items from Ilya:

  The first patch fixes the RBD readahead to grab full objects.  The
  second fixes the write ops to prevent undue promotion when a cache
  tier is configured on the server side"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client:
  rbd: use writefull op for object size writes
  rbd: set max_sectors explicitly

Pull power management and ACPI fixes from Rafael Wysocki:
 "These fix two recent regressions (ACPICA, the generic power domains
  framework) and one crash that may happen on specific hardware
  supported since 4.1 (intel_pstate).

  Specifics:

   - Fix a regression introduced by a recent ACPICA cleanup that
     uncovered a latent bug (Lv Zheng).

   - Fix a recent regression in the generic power domains framework that
     may cause it to violate PM QoS latency constraints in some cases
     (Ulf Hansson).

   - Fix an intel_pstate driver crash on the Knights Landing chips that
     do not update the MPERF counter as often as expected by the driver
     which may result in a divide by 0 (Srinivas Pandruvada)"

* tag 'pm+acpi-4.3-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  cpufreq: intel_pstate: Fix divide by zero on Knights Landing (KNL)
  ACPICA: Tables: Fix FADT dependency regression
  PM / Domains: Fix validation of latency constraints in genpd governor

Pull drm fixes from Dave Airlie:
 "Nothing too crazy or exciting:

   - two MAINTAINERS entries that I didn't see the point in delaying.
   - one drm mst fix to stop sending uninitialised data to monitors
   - two amdgpu fixes
   - one radeon mst tiling fix
   - one vmwgfx regression fix
   - one virtio warning fix.

  I have found one locking problem that needs a bit of reorg to fix, but
  I'm not sure it's worth putting in -fixes as I don't think we've seen
  it hit in the real world ever, I just found it using the virtio-gpu
  driver when working on it.  I'll possibly send it next week once I've
  time to discuss with Daniel"

* 'drm-fixes' of git://people.freedesktop.org/~airlied/linux:
  drm/virtio: use %llu format string form atomic64_t
  MAINTAINERS: Add myself as maintainer for the gma500 driver
  MAINTAINERS: add a maintainer for the atmel-hlcdc DRM driver
  drm/amdgpu: Keep the pflip interrupts always enabled v7
  drm/amdgpu: adjust default dispclk (v2)
  drm/dp/mst: make mst i2c transfer code more robust.
  drm/radeon: attach tile property to mst connector
  drm/vmwgfx: Fix kernel NULL pointer dereference on older hardware

Pull powerpc fixes from Michael Ellerman:
 - Re-enable CONFIG_SCSI_DH in our defconfigs
 - Remove unused os_area_db_id_video_mode
 - cxl: fix leak of IRQ names in cxl_free_afu_irqs() from Andrew
 - cxl: fix leak of ctx->irq_bitmap when releasing context via kernel API from Andrew
 - cxl: fix leak of ctx->mapping when releasing kernel API contexts from Andrew
 - cxl: Workaround malformed pcie packets on some cards from Philippe
 - cxl: Fix number of allocated pages in SPA from Christophe Lombard
 - Fix checkstop in native_hpte_clear() with lockdep from Cyril
 - Panic on unhandled Machine Check on powernv from Daniel
 - selftests/powerpc: Fix build failure of load_unaligned_zeropad test

* tag 'powerpc-4.3-4' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux:
  selftests/powerpc: Fix build failure of load_unaligned_zeropad test
  powerpc/powernv: Panic on unhandled Machine Check
  powerpc: Fix checkstop in native_hpte_clear() with lockdep
  cxl: Fix number of allocated pages in SPA
  cxl: Workaround malformed pcie packets on some cards
  cxl: fix leak of ctx->mapping when releasing kernel API contexts
  cxl: fix leak of ctx->irq_bitmap when releasing context via kernel API
  cxl: fix leak of IRQ names in cxl_free_afu_irqs()
  powerpc/ps3: Remove unused os_area_db_id_video_mode
  powerpc/configs: Re-enable CONFIG_SCSI_DH

Merge misc fixes from Andrew Morton:
 "6 fixes"

* emailed patches from Andrew Morton <akpm@linux-foundation.org>:
  sh: add copy_user_page() alias for __copy_user()
  lib/Kconfig: ZLIB_DEFLATE must select BITREVERSE
  mm, dax: fix DAX deadlocks
  memcg: convert threshold to bytes
  builddeb: remove debian/files before build
  mm, fs: obey gfp_mapping for add_to_page_cache()

copy_user_page() is needed by DAX.  Without this we get a compile error
for DAX on SH:

  fs/dax.c:280:2: error: implicit declaration of function `copy_user_page' [-Werror=implicit-function-declaration]
    copy_user_page(vto, (void __force *)vfrom, vaddr, to);
      ^

This was done with a random config that happened to include DAX support.

This patch has only been compile tested.
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Matthew Wilcox <willy@linux.intel.com>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/built-in.o: In function `__bitrev32':
deftree.c:(.text+0x1e799): undefined reference to `byte_rev_table'
deftree.c:(.text+0x1e7a0): undefined reference to `byte_rev_table'
deftree.c:(.text+0x1e7b4): undefined reference to `byte_rev_table'
deftree.c:(.text+0x1e7c1): undefined reference to `byte_rev_table'

Anything which uses bitrevX() has to select BITREVERSE, to grab
lib/bitrev.o.
Reported-by: Jim Davis <jim.epost@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>