AMD CPUs don't reinitialize the SS descriptor on SYSRET, so SYSRET with
SS == 0 results in an invalid usermode state in which SS is apparently
equal to __USER_DS but causes #SS if used.

Work around the issue by setting SS to __KERNEL_DS __switch_to, thus
ensuring that SYSRET never happens with SS set to NULL.

This was exposed by a recent vDSO cleanup.

Fixes: e7d6eefaaa44 x86/vdso32/syscall.S: Do not load __USER32_DS to %ss
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Peter Anvin <hpa@zytor.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Brian Gerst <brgerst@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull intel drm fixes from Dave Airlie.

* 'drm-fixes' of git://people.freedesktop.org/~airlied/linux:
  drm/i915: vlv: fix save/restore of GFX_MAX_REQ_COUNT reg
  drm/i915: Workaround to avoid lite restore with HEAD==TAIL
  drm/i915: cope with large i2c transfers

Pull intel iommu updates from David Woodhouse:
 "This lays a little of the groundwork for upcoming Shared Virtual
  Memory support — fixing some bogus #defines for capability bits and
  adding the new ones, and starting to use the new wider page tables
  where we can, in anticipation of actually filling in the new fields
  therein.

  It also allows graphics devices to be assigned to VM guests again.
  This got broken in 3.17 by disallowing assignment of RMRR-afflicted
  devices.  Like USB, we do understand why there's an RMRR for graphics
  devices — and unlike USB, it's actually sane.  So we can make an
  exception for graphics devices, just as we do USB controllers.

  Finally, tone down the warning about the X2APIC_OPT_OUT bit, due to
  persistent requests.  X2APIC_OPT_OUT was added to the spec as a nasty
  hack to allow broken BIOSes to forbid us from using X2APIC when they
  do stupid and invasive things and would break if we did.

  Someone noticed that since Windows doesn't have full IOMMU support for
  DMA protection, setting the X2APIC_OPT_OUT bit made Windows avoid
  initialising the IOMMU on the graphics unit altogether.

  This means that it would be available for use in "driver mode", where
  the IOMMU registers are made available through a BAR of the graphics
  device and the graphics driver can do SVM all for itself.

  So they started setting the X2APIC_OPT_OUT bit on *all* platforms with
  SVM capabilities.  And even the platforms which *might*, if the
  planets had been aligned correctly, possibly have had SVM capability
  but which in practice actually don't"

* git://git.infradead.org/intel-iommu:
  iommu/vt-d: support extended root and context entries
  iommu/vt-d: Add new extended capabilities from v2.3 VT-d specification
  iommu/vt-d: Allow RMRR on graphics devices too
  iommu/vt-d: Print x2apic opt out info instead of printing a warning
  iommu/vt-d: kill bogus ecap_niotlb_iunits()

Pull i2c fixes from Wolfram Sang:
 "This has a mixture of merge window cleanups and bugfixes"

* 'i2c/for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux:
  i2c: st: add include for pinctrl
  i2c: mux: use proper dev when removing "channel-X" symlinks
  i2c: digicolor: remove duplicate include
  i2c: Mark adapter devices with pm_runtime_no_callbacks
  i2c: pca-platform: fix broken email address
  i2c: mxs: fix broken email address
  i2c: rk3x: report number of messages transmitted

Pull btrfs fixes from Chris Mason:
 "Filipe hit two problems in my block group cache patches.  We finalized
  the fixes last week and ran through more tests"

* 'for-linus-4.1' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs:
  Btrfs: prevent list corruption during free space cache processing
  Btrfs: fix inode cache writeout

three fixes for i915.

* tag 'drm-intel-next-fixes-2015-04-25' of git://anongit.freedesktop.org/drm-intel:
  drm/i915: vlv: fix save/restore of GFX_MAX_REQ_COUNT reg
  drm/i915: Workaround to avoid lite restore with HEAD==TAIL
  drm/i915: cope with large i2c transfers

Pull NFS client updates from Trond Myklebust:
 "Another set of mainly bugfixes and a couple of cleanups.  No new
  functionality in this round.

  Highlights include:

  Stable patches:
   - Fix a regression in /proc/self/mountstats
   - Fix the pNFS flexfiles O_DIRECT support
   - Fix high load average due to callback thread sleeping

  Bugfixes:
   - Various patches to fix the pNFS layoutcommit support
   - Do not cache pNFS deviceids unless server notifications are enabled
   - Fix a SUNRPC transport reconnection regression
   - make debugfs file creation failure non-fatal in SUNRPC
   - Another fix for circular directory warnings on NFSv4 "junctioned"
     mountpoints
   - Fix locking around NFSv4.2 fallocate() support
   - Truncating NFSv4 file opens should also sync O_DIRECT writes
   - Prevent infinite loop in rpcrdma_ep_create()

  Features:
   - Various improvements to the RDMA transport code's handling of
     memory registration
   - Various code cleanups"

* tag 'nfs-for-4.1-1' of git://git.linux-nfs.org/projects/trondmy/linux-nfs: (55 commits)
  fs/nfs: fix new compiler warning about boolean in switch
  nfs: Remove unneeded casts in nfs
  NFS: Don't attempt to decode missing directory entries
  Revert "nfs: replace nfs_add_stats with nfs_inc_stats when add one"
  NFS: Rename idmap.c to nfs4idmap.c
  NFS: Move nfs_idmap.h into fs/nfs/
  NFS: Remove CONFIG_NFS_V4 checks from nfs_idmap.h
  NFS: Add a stub for GETDEVICELIST
  nfs: remove WARN_ON_ONCE from nfs_direct_good_bytes
  nfs: fix DIO good bytes calculation
  nfs: Fetch MOUNTED_ON_FILEID when updating an inode
  sunrpc: make debugfs file creation failure non-fatal
  nfs: fix high load average due to callback thread sleeping
  NFS: Reduce time spent holding the i_mutex during fallocate()
  NFS: Don't zap caches on fallocate()
  xprtrdma: Make rpcrdma_{un}map_one() into inline functions
  xprtrdma: Handle non-SEND completions via a callout
  xprtrdma: Add "open" memreg op
  xprtrdma: Add "destroy MRs" memreg op
  xprtrdma: Add "reset MRs" memreg op
  ...

Pull fourth vfs update from Al Viro:
 "d_inode() annotations from David Howells (sat in for-next since before
  the beginning of merge window) + four assorted fixes"

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  RCU pathwalk breakage when running into a symlink overmounting something
  fix I_DIO_WAKEUP definition
  direct-io: only inc/dec inode->i_dio_count for file systems
  fs/9p: fix readdir()
  VFS: assorted d_backing_inode() annotations
  VFS: fs/inode.c helpers: d_inode() annotations
  VFS: fs/cachefiles: d_backing_inode() annotations
  VFS: fs library helpers: d_inode() annotations
  VFS: assorted weird filesystems: d_inode() annotations
  VFS: normal filesystems (and lustre): d_inode() annotations
  VFS: security/: d_inode() annotations
  VFS: security/: d_backing_inode() annotations
  VFS: net/: d_inode() annotations
  VFS: net/unix: d_backing_inode() annotations
  VFS: kernel/: d_inode() annotations
  VFS: audit: d_backing_inode() annotations
  VFS: Fix up some ->d_inode accesses in the chelsio driver
  VFS: Cachefiles should perform fs modifications on the top layer only
  VFS: AF_UNIX sockets should call mknod on the top layer only

Pull more power management and ACPI updates from Rafael Wysocki:
 "These are fixes mostly (intel_pstate, ACPI core, ACPI EC driver,
  cpupower tool), a new CPU ID for the Intel RAPL driver and one
  intel_pstate driver improvement that didn't make it to my previous
  pull requests due to timing.

  Specifics:

   - Fix a build warning in the intel_pstate driver showing up in
     non-SMP builds (Borislav Petkov)

   - Change one of the intel_pstate's P-state selection parameters for
     Baytrail and Cherrytrail CPUs to significantly improve performance
     at the cost of a small increase in energy consumption (Kristen
     Carlson Accardi)

   - Fix a NULL pointer dereference in the ACPI EC driver due to an
     unsafe list walk in the query handler removal routine (Chris
     Bainbridge)

   - Get rid of a false-positive lockdep warning in the ACPI container
     hot-remove code (Rafael J Wysocki)

   - Prevent the ACPI device enumeration code from creating device
     objects of a wrong type in some cases (Rafael J Wysocki)

   - Add Skylake processors support to the Intel RAPL power capping
     driver (Brian Bian)

   - Drop the stale MAINTAINERS entry for the ACPI dock driver that is
     regarded as part of the ACPI core and maintained along with it now
     (Chao Yu)

   - Fix cpupower tool breakage caused by a library API change in libpci
     3.3.0 (Lucas Stach)"

* tag 'pm+acpi-4.1-rc1-2' of git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm:
  ACPI / scan: Add a scan handler for PRP0001
  ACPI / scan: Annotate physical_node_lock in acpi_scan_is_offline()
  ACPI / EC: fix NULL pointer dereference in acpi_ec_remove_query_handler()
  MAINTAINERS: remove maintainship entry of docking station driver
  powercap / RAPL: Add support for Intel Skylake processors
  cpufreq: intel_pstate: Fix an annoying !CONFIG_SMP warning
  intel_pstate: Change the setpoint for Atom params
  cpupower: fix breakage from libpci API change