This patch has tcmu internally queue cmds if its ring buffer
is full. It also makes the TCMU_GLOBAL_MAX_BLOCKS limit a
hint instead of a hard limit, so we do not have to add any
new locks/atomics in the main IO path except when IO is not
running.

This fixes the following bugs:

1. We cannot sleep from the submitting context because it might be
called from a target recv context. This results in transport level
commands timing out. For example if the ring is full, we would
sleep, and a iscsi initiator would send a iscsi ping/nop which
times out because the target's recv thread is sleeping here.

2. Devices were not fairly scheduled to run when they hit the global
limit so they could time out waiting for ring space while others
got run.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

We do not really save a lot by trying to increase thresh
a multiple of the existing value. This just simplifies the
code by increasing it to whatever is needed for the command
being executed.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

In the next patches we will call queue_cmd_ring from the submitting
context and also the completion path. This changes the queue_cmd_ring
return code so in the next patches we can return a sense_reason_t
and also signal if a command was requeued.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

Add some comments to make the scatter code to be more readable,
and drop unused arg to new_iov.
Signed-off-by: Xiubo Li <lixiubo@cmss.chinamobile.com>
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

The blocks_left calculation does not account for free blocks
between 0 and thresh, so we could be queueing/waiting when
there are enough blocks free.

This has us add in the blocks between 0 and thresh as well as
at the end from thresh to DATA_BLOCK_BITS.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

scatter_data_area always returns 0, so stop checking
for errors.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

If we cannot setup a cmd because we run out of ring space
or global pages release the blocks before sleeping. This
prevents a deadlock where dev0 has waiting_blocks set and
needs N blocks, but dev1 to devX have each allocated N / X blocks
and also hit the global block limit so they went to sleep.

find_free_blocks is not able to take the sleeping dev's
blocks becaause their waiting_blocks is set and even
if it was not the block returned by find_last_bit could equal
dbi_max. The latter will probably never happen because
DATA_BLOCK_BITS is so high but in the next patches
DATA_BLOCK_BITS and TCMU_GLOBAL_MAX_BLOCKS will be settable so
it might be lower and could happen.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

No need for the commands_lock. The cmdr_lock is already held during
idr addition and deletion, so just grab it during traversal.

Note: This also fixes a issue where we should have been using at
least _bh locking in tcmu_handle_completions when taking the commands
lock to prevent the case where tcmu_handle_completions could be
interrupted by a timer softirq while the commands_lock is held.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

This moves the expired command completion handling to
the unmap wq, so the next patch can use a mutex
in tcmu_check_expired_cmd.

Note:
tcmu_device_timedout's use of spin_lock_irq was not needed.
The commands_lock is used between thread context (tcmu_queue_cmd_ring
and tcmu_irqcontrol (even though this is named irqcontrol it is not
run in irq context)) and timer/bh context. In the timer/bh context
bhs are disabled, so you need to use the _bh lock calls from the
thread context callers.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

If the unmap thread has already run find_free_blocks
but not yet run prepare_to_wait when a wake_up(&unmap_wait)
call is done, the unmap thread is going to miss the wake
call. Instead of adding checks for if new waiters were added
this just has us use a work queue which will run us again
in this type of case.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

Separate unmap_thread_fn to make it easier to read.

Note: this patch does not fix the bug where we might
miss a wake up call. The next patch will fix that.
This patch only separates the code into functions.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

Have unmap_thread_fn use tcmu_blocks_release.
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

The page addr should be update.
Signed-off-by: tangwenji <tang.wenji@zte.com.cn>
Signed-off-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

iscsi_parse_pr_out_transport_id launders the const away via a call to
strstr(), and then modifies the buffer (writing a nul byte) through
the return value. It's cleaner to be honest and simply declare the
parameter as "char*", fixing up the call chain, and allowing us to
drop the cast in the return statement.

Amusingly, the two current callers found it necessary to cast a
non-const pointer to a const.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

Pull x86 fixes from Thomas Gleixner:
 "A couple of fixlets for x86:

   - Fix the ESPFIX double fault handling for 5-level pagetables

   - Fix the commandline parsing for 'apic=' on 32bit systems and update
     documentation

   - Make zombie stack traces reliable

   - Fix kexec with stack canary

   - Fix the delivery mode for APICs which was missed when the x86
     vector management was converted to single target delivery. Caused a
     regression due to the broken hardware which ignores affinity
     settings in lowest prio delivery mode.

   - Unbreak modules when AMD memory encryption is enabled

   - Remove an unused parameter of prepare_switch_to"

* 'x86/urgent' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/apic: Switch all APICs to Fixed delivery mode
  x86/apic: Update the 'apic=' description of setting APIC driver
  x86/apic: Avoid wrong warning when parsing 'apic=' in X86-32 case
  x86-32: Fix kexec with stack canary (CONFIG_CC_STACKPROTECTOR)
  x86: Remove unused parameter of prepare_switch_to
  x86/stacktrace: Make zombie stack traces reliable
  x86/mm: Unbreak modules that use the DMA API
  x86/build: Make isoimage work on Debian
  x86/espfix/64: Fix espfix double-fault handling on 5-level systems

Pull x86 page table isolation fixes from Thomas Gleixner:
 "Four patches addressing the PTI fallout as discussed and debugged
  yesterday:

   - Remove stale and pointless TLB flush invocations from the hotplug
     code

   - Remove stale preempt_disable/enable from __native_flush_tlb()

   - Plug the memory leak in the write_ldt() error path"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/ldt: Make LDT pgtable free conditional
  x86/ldt: Plug memory leak in error path
  x86/mm: Remove preempt_disable/enable() from __native_flush_tlb()
  x86/smpboot: Remove stale TLB flush invocations

Pull timer fixes from Thomas Gleixner:
 "A pile of fixes for long standing issues with the timer wheel and the
  NOHZ code:

   - Prevent timer base confusion accross the nohz switch, which can
     cause unlocked access and data corruption

   - Reinitialize the stale base clock on cpu hotplug to prevent subtle
     side effects including rollovers on 32bit

   - Prevent an interrupt storm when the timer softirq is already
     pending caused by tick_nohz_stop_sched_tick()

   - Move the timer start tracepoint to a place where it actually makes
     sense

   - Add documentation to timerqueue functions as they caused confusion
     several times now"

* 'timers-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  timerqueue: Document return values of timerqueue_add/del()
  timers: Invoke timer_start_debug() where it makes sense
  nohz: Prevent a timer interrupt storm in tick_nohz_stop_sched_tick()
  timers: Reinitialize per cpu bases on hotplug
  timers: Use deferrable base independent of base::nohz_active

Pull smp fixlet from Thomas Gleixner:
 "A trivial build warning fix for newer compilers"

* 'smp-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  cpu/hotplug: Move inline keyword at the beginning of declaration

Pull scheduler fixes from Thomas Gleixner:
 "Three patches addressing the fallout of the CPU_ISOLATION changes
  especially with NO_HZ_FULL plus documentation of boot parameter
  dependency"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/isolation: Document boot parameters dependency on CONFIG_CPU_ISOLATION=y
  sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default
  sched/isolation: Make CONFIG_NO_HZ_FULL select CONFIG_CPU_ISOLATION

Pull perf fixes from Thomas Gleixner:

 - plug a memory leak in the intel pmu init code

 - clang fixes

 - tooling fix to avoid including kernel headers

 - a fix for jvmti to generate correct debug information for inlined
   code

 - replace backtick with a regular shell function

 - fix the build in hardened environments

* 'perf-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  perf/x86/intel: Plug memory leak in intel_pmu_init()
  x86/asm: Allow again using asm.h when building for the 'bpf' clang target
  tools arch s390: Do not include header files from the kernel sources
  perf jvmti: Generate correct debug information for inlined code
  perf tools: Fix up build in hardened environments
  perf tools: Use shell function for perl cflags retrieval

Pull irq fixes from Thomas Gleixner:
 "A rather large update after the kaisered maintainer finally found time
  to handle regression reports.

   - The larger part addresses a regression caused by the x86 vector
     management rework.

     The reservation based model does not work reliably for MSI
     interrupts, if they cannot be masked (yes, yet another hw
     engineering trainwreck). The reason is that the reservation mode
     assigns a dummy vector when the interrupt is allocated and switches
     to a real vector when the interrupt is requested.

     If the MSI entry cannot be masked then the initialization might
     raise an interrupt before the interrupt is requested, which ends up
     as spurious interrupt and causes device malfunction and worse. The
     fix is to exclude MSI interrupts which do not support masking from
     reservation mode and assign a real vector right away.

   - Extend the extra lockdep class setup for nested interrupts with a
     class for the recently added irq_desc::request_mutex so lockdep can
     differeniate and does not emit false positive warnings.

   - A ratelimit guard for the bad irq printout so in case a bad irq
     comes back immediately the system does not drown in dmesg spam"

* 'irq-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  genirq/msi, x86/vector: Prevent reservation mode for non maskable MSI
  genirq/irqdomain: Rename early argument of irq_domain_activate_irq()
  x86/vector: Use IRQD_CAN_RESERVE flag
  genirq: Introduce IRQD_CAN_RESERVE flag
  genirq/msi: Handle reactivation only on success
  gpio: brcmstb: Make really use of the new lockdep class
  genirq: Guard handle_bad_irq log messages
  kernel/irq: Extend lockdep class for request mutex

Pull objtool fixes from Thomas Gleixner:
 "Three fixlets for objtool:

   - Address two segfaults related to missing parameter and clang
     objects

   - Make it compile clean with clang"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  objtool: Fix seg fault with clang-compiled objects
  objtool: Fix seg fault caused by missing parameter
  objtool: Fix Clang enum conversion warning

Pull char/misc fixes from Greg KH:
 "Here are six small fixes of some of the char/misc drivers that have
  been sent in to resolve reported issues.

  Nothing major, a binder use-after-free fix, some thunderbolt bugfixes,
  a hyper-v bugfix, and an nvmem driver fix. All of these have been in
  linux-next with no reported issues for a while"

* tag 'char-misc-4.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
  nvmem: meson-mx-efuse: fix reading from an offset other than 0
  binder: fix proc->files use-after-free
  vmbus: unregister device_obj->channels_kset
  thunderbolt: Mask ring interrupt properly when polling starts
  MAINTAINERS: Add thunderbolt.rst to the Thunderbolt driver entry
  thunderbolt: Make pathname to force_power shorter

Merge tag 'driver-core-4.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull driver core fixes from Greg KH:
 "Here are two driver core fixes for 4.15-rc6, resolving some reported
  issues.

  The first is a cacheinfo fix for DT based systems to resolve a
  reported issue that has been around for a while, and the other is to
  resolve a regression in the kobject uevent code that showed up in
  4.15-rc1.

  Both have been in linux-next for a while with no reported issues"

* tag 'driver-core-4.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core:
  kobject: fix suppressing modalias in uevents delivered over netlink
  drivers: base: cacheinfo: fix cache type for non-architected system cache

Pull staging fixes from Greg KH:
 "Here are three staging driver fixes for 4.15-rc6

  The first resolves a bug in the lustre driver that came about due to a
  broken cleanup patch, due to crazy list usage in that codebase.

  The remaining two are ion driver fixes, finally getting the CMA
  interaction to work properly, resolving two regressions in that area
  of the code.

  All have been in linux-next with no reported issues for a while"

* tag 'staging-4.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging:
  staging: android: ion: Fix dma direction for dma_sync_sg_for_cpu/device
  staging: ion: Fix ion_cma_heap allocations
  staging: lustre: lnet: Fix recent breakage from list_for_each conversion

Pull TTY fix from Greg KH:
 "Here is a single tty fix for a reported issue that you wrote the patch
  for :)

  It's been in linux-next for a week or so with no reported issues"

* tag 'tty-4.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/tty:
  n_tty: fix EXTPROC vs ICANON interaction with TIOCINQ (aka FIONREAD)

Pull USB/PHY fixes from Greg KH:
 "Here are a number of small USB and PHY driver fixes for 4.15-rc6.

  Nothing major, but there are a number of regression fixes in here that
  resolve issues that have been reported a bunch. There are also the
  usual xhci fixes as well as a number of new usb serial device ids.

  All of these have been in linux-next for a while with no reported
  issues"

* tag 'usb-4.15-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb:
  usb: xhci: Add XHCI_TRUST_TX_LENGTH for Renesas uPD720201
  xhci: Fix use-after-free in xhci debugfs
  xhci: Fix xhci debugfs NULL pointer dereference in resume from hibernate
  USB: serial: ftdi_sio: add id for Airbus DS P8GR
  usb: Add device quirk for Logitech HD Pro Webcam C925e
  usb: add RESET_RESUME for ELSA MicroLink 56K
  usbip: fix usbip bind writing random string after command in match_busid
  usbip: stub_rx: fix static checker warning on unnecessary checks
  usbip: prevent leaking socket pointer address in messages
  usbip: stub: stop printing kernel pointer addresses in messages
  usbip: vhci: stop printing kernel pointer addresses in messages
  USB: Fix off by one in type-specific length check of BOS SSP capability
  USB: serial: option: adding support for YUGA CLM920-NC5
  phy: rcar-gen3-usb2: select USB_COMMON
  phy: rockchip-typec: add pm_runtime_disable in err case
  phy: cpcap-usb: Fix platform_get_irq_byname's error checking.
  phy: tegra: fix device-tree node lookups
  USB: serial: qcserial: add Sierra Wireless EM7565
  USB: serial: option: add support for Telit ME910 PID 0x1101
  USB: chipidea: msm: fix ulpi-node lookup

The blackfin architecture has seen no maintainer action of any kind since
April 2015.  No new code, no pull requests, no acks to patches, no response
to mails, nothing.

The web site has an expired certificate (expiration Sep 2017, issued in
2013), the mailing list sees no answers either, with one exception:

  https://sourceforge.net/p/adi-buildroot/mailman/adi-buildroot-devel/
  >
  > Steven is no longer working on this for ADI. Acked by me if this works. Thanks.
  >
  > Best regards,
  > Aaron Wu
  > Analog Devices Inc.

But, Aaron doesn't seem to respond to queries either.
Signed-off-by: Adam Borowski <kilobyte@angband.pl>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull sparc bugfix from David Miller.

* git://git.kernel.org/pub/scm/linux/kernel/git/davem/sparc:
  sparc64: repair calling incorrect hweight function from stubs

Andy prefers to be paranoid about the pagetable free in the error path of
write_ldt(). Make it conditional and warn whenever the installment of a
secondary LDT fails.
Requested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

The error path in write_ldt() tries to free 'old_ldt' instead of the newly
allocated 'new_ldt', resulting in a memory leak. It also misses to clean up a
half populated LDT pagetable, which is not a leak as it gets cleaned up
when the process exits.

Free both the potentially half populated LDT pagetable and the newly
allocated LDT struct. This can be done unconditionally because once an LDT
is mapped subsequent maps will succeed, because the PTE page is already
populated and the two LDTs fit into that single page.
Reported-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: f55f0501 ("x86/pti: Put the LDT in its own PGD if PTI is on")
Link: http://lkml.kernel.org/r/alpine.DEB.2.20.1712311121340.1899@nanosSigned-off-by: Ingo Molnar <mingo@kernel.org>

The preempt_disable/enable() pair in __native_flush_tlb() was added in
commit:

  5cf0791d ("x86/mm: Disable preemption during CR3 read+write")

... to protect the UP variant of flush_tlb_mm_range().

That preempt_disable/enable() pair should have been added to the UP variant
of flush_tlb_mm_range() instead.

The UP variant was removed with commit:

  ce4a4e56 ("x86/mm: Remove the UP asm/tlbflush.h code, always use the (formerly) SMP code")

... but the preempt_disable/enable() pair stayed around.

The latest change to __native_flush_tlb() in commit:

  6fd166aa ("x86/mm: Use/Fix PCID to optimize user/kernel switches")

... added an access to a per CPU variable outside the preempt disabled
regions, which makes no sense at all. __native_flush_tlb() must always
be called with at least preemption disabled.

Remove the preempt_disable/enable() pair and add a WARN_ON_ONCE() to catch
bad callers independent of the smp_processor_id() debugging.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171230211829.679325424@linutronix.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

smpboot_setup_warm_reset_vector() and smpboot_restore_warm_reset_vector()
invoke local_flush_tlb() for no obvious reason.

Digging in history revealed that the original code in the 2.1 era added
those because the code manipulated a swapper_pg_dir pagetable entry. The
pagetable manipulation was removed long ago in the 2.3 timeframe, but the
TLB flush invocations stayed around forever.

Remove them along with the pointless pr_debug()s which come from the same 2.1
change.
Reported-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@vger.kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linuxfoundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171230211829.586548655@linutronix.deSigned-off-by: Ingo Molnar <mingo@kernel.org>

Pull SCSI fixes from James Bottomley:
 "Two simple fixes, both of which cause I/O hangs.

  The storvsc one is from the hyper-v which can hang under certain hot
  add/remove conditions and the other is generally, where removing a
  target and a device in close proximity can result in the release
  method being executed twice (and subsequent list and other corruption
  and an eventual panic)"

* tag 'scsi-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi:
  scsi: storvsc: Fix scsi_cmd error assignments in storvsc_handle_error
  scsi: core: check for device state in __scsi_remove_target()

Fix a seg fault which happens when an input file provided to 'objtool
orc generate' doesn't have a '.shstrtab' section (for instance, object
files produced by clang don't have this section).
Signed-off-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/c0f2231683e9bed40fac1f13ce2c33b8389854bc.1514666459.git.jpoimboe@redhat.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

Fix a seg fault when no parameter is provided to 'objtool orc'.
Signed-off-by: Simon Ser <contact@emersion.fr>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/9172803ec7ebb72535bcd0b7f966ae96d515968e.1514666459.git.jpoimboe@redhat.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

Pull HID fixes from Jiri Kosina:

 - two cosmetic fixes from Daniel Axtens and Hans de Goede

 - fix for I2C command mismatch fix for cp2112 driver from Eudean Sun

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid:
  HID: core: lower log level for unknown main item tags to warnings
  HID: holtekff: move MODULE_* parameters out of #ifdef block
  HID: cp2112: Fix I2C_BLOCK_DATA transactions

It appears that hardened gentoo enables "-fstack-check" by default for
gcc.

That doesn't work _at_all_ for the kernel, because the kernel stack
doesn't act like a user stack at all: it's much smaller, and it doesn't
auto-expand on use.  So the extra "probe one page below the stack" code
generated by -fstack-check just breaks the kernel in horrible ways,
causing infinite double faults etc.

[ I have to say, that the particular code gcc generates looks very
  stupid even for user space where it works, but that's a separate
  issue.  ]
Reported-and-tested-by: Alexander Tsoy <alexander@tsoy.me>
Reported-and-tested-by: Toralf Förster <toralf.foerster@gmx.de>
Cc: stable@kernel.org
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Pull x86 page table isolation updates from Thomas Gleixner:
 "This is the final set of enabling page table isolation on x86:

   - Infrastructure patches for handling the extra page tables.

   - Patches which map the various bits and pieces which are required to
     get in and out of user space into the user space visible page
     tables.

   - The required changes to have CR3 switching in the entry/exit code.

   - Optimizations for the CR3 switching along with documentation how
     the ASID/PCID mechanism works.

   - Updates to dump pagetables to cover the user space page tables for
     W+X scans and extra debugfs files to analyze both the kernel and
     the user space visible page tables

  The whole functionality is compile time controlled via a config switch
  and can be turned on/off on the command line as well"

* 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (32 commits)
  x86/ldt: Make the LDT mapping RO
  x86/mm/dump_pagetables: Allow dumping current pagetables
  x86/mm/dump_pagetables: Check user space page table for WX pages
  x86/mm/dump_pagetables: Add page table directory to the debugfs VFS hierarchy
  x86/mm/pti: Add Kconfig
  x86/dumpstack: Indicate in Oops whether PTI is configured and enabled
  x86/mm: Clarify the whole ASID/kernel PCID/user PCID naming
  x86/mm: Use INVPCID for __native_flush_tlb_single()
  x86/mm: Optimize RESTORE_CR3
  x86/mm: Use/Fix PCID to optimize user/kernel switches
  x86/mm: Abstract switching CR3
  x86/mm: Allow flushing for future ASID switches
  x86/pti: Map the vsyscall page if needed
  x86/pti: Put the LDT in its own PGD if PTI is on
  x86/mm/64: Make a full PGD-entry size hole in the memory map
  x86/events/intel/ds: Map debug buffers in cpu_entry_area
  x86/cpu_entry_area: Add debugstore entries to cpu_entry_area
  x86/mm/pti: Map ESPFIX into user space
  x86/mm/pti: Share entry text PMD
  x86/entry: Align entry text section to PMD boundary
  ...