1. 30 Oct, 2019 1 commit
  2. 23 Oct, 2019 8 commits
  3. 14 Oct, 2019 1 commit
    • Miaoqing Pan's avatar
      ath10k: fix latency issue for QCA988x · d79749f7
      Miaoqing Pan authored
      (kvalo: cherry picked from commit 1340cc63 in
      wireless-drivers-next to wireless-drivers as this a frequently reported
      regression)
      
      Bad latency is found on QCA988x, the issue was introduced by
      commit 4504f0e5 ("ath10k: sdio: workaround firmware UART
      pin configuration bug"). If uart_pin_workaround is false, this
      change will set uart pin even if uart_print is false.
      
      Tested HW: QCA9880
      Tested FW: 10.2.4-1.0-00037
      
      Fixes: 4504f0e5 ("ath10k: sdio: workaround firmware UART pin configuration bug")
      Signed-off-by: default avatarMiaoqing Pan <miaoqing@codeaurora.org>
      Signed-off-by: default avatarKalle Valo <kvalo@codeaurora.org>
      d79749f7
  4. 09 Oct, 2019 11 commits
    • Kalle Valo's avatar
      Merge tag 'iwlwifi-for-kalle-2019-10-09' of... · 3aed8837
      Kalle Valo authored
      Merge tag 'iwlwifi-for-kalle-2019-10-09' of git://git.kernel.org/pub/scm/linux/kernel/git/iwlwifi/iwlwifi-fixes
      
      First batch of fixes intended for v5.4
      
      * fix for an ACPI table parsing bug;
      * a fix for a NULL pointer dereference in the cfg with specific
        devices;
      * fix the rb_allocator;
      * prevent multiple phy configuration with new devices;
      * fix a race-condition in the rx queue;
      * prevent a couple of memory leaks;
      * fix initialization of 3168 devices (the infamous BAD_COMMAND bug);
      * fix recognition of some newer systems with integrated MAC;
      3aed8837
    • Luca Coelho's avatar
      iwlwifi: pcie: change qu with jf devices to use qu configuration · aa0cc7dd
      Luca Coelho authored
      There were a bunch of devices with qu and jf that were loading the
      configuration with pu and jf, which is wrong.  Fix them all
      accordingly.  Additionally, remove 0x1010 and 0x1210 subsytem IDs from
      the list, since they are obviously wrong, and 0x0044 and 0x0244, which
      were duplicate.
      
      Cc: stable@vger.kernel.org # 5.1+
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      aa0cc7dd
    • Luca Coelho's avatar
      iwlwifi: exclude GEO SAR support for 3168 · 12e36d98
      Luca Coelho authored
      We currently support two NICs in FW version 29, namely 7265D and 3168.
      Out of these, only 7265D supports GEO SAR, so adjust the function that
      checks for it accordingly.
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      Fixes: f5a47fae ("iwlwifi: mvm: fix version check for GEO_TX_POWER_LIMIT support")
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      12e36d98
    • Navid Emamdoost's avatar
      iwlwifi: pcie: fix memory leaks in iwl_pcie_ctxt_info_gen3_init · 0f4f1994
      Navid Emamdoost authored
      In iwl_pcie_ctxt_info_gen3_init there are cases that the allocated dma
      memory is leaked in case of error.
      
      DMA memories prph_scratch, prph_info, and ctxt_info_gen3 are allocated
      and initialized to be later assigned to trans_pcie. But in any error case
      before such assignment the allocated memories should be released.
      
      First of such error cases happens when iwl_pcie_init_fw_sec fails.
      Current implementation correctly releases prph_scratch. But in two
      sunsequent error cases where dma_alloc_coherent may fail, such
      releases are missing.
      
      This commit adds release for prph_scratch when allocation for
      prph_info fails, and adds releases for prph_scratch and prph_info when
      allocation for ctxt_info_gen3 fails.
      
      Fixes: 2ee82402 ("iwlwifi: pcie: support context information for 22560 devices")
      Signed-off-by: default avatarNavid Emamdoost <navid.emamdoost@gmail.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      0f4f1994
    • Navid Emamdoost's avatar
      iwlwifi: dbg_ini: fix memory leak in alloc_sgtable · b4b814fe
      Navid Emamdoost authored
      In alloc_sgtable if alloc_page fails, the alocated table should be
      released.
      Signed-off-by: default avatarNavid Emamdoost <navid.emamdoost@gmail.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      b4b814fe
    • Johannes Berg's avatar
      iwlwifi: pcie: fix rb_allocator workqueue allocation · 8188a18e
      Johannes Berg authored
      We don't handle failures in the rb_allocator workqueue allocation
      correctly. To fix that, move the code earlier so the cleanup is
      easier and we don't have to undo all the interrupt allocations in
      this case.
      Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      8188a18e
    • Johannes Berg's avatar
      iwlwifi: pcie: fix indexing in command dump for new HW · 08326a97
      Johannes Berg authored
      We got a crash in iwl_trans_pcie_get_cmdlen(), while the TFD was
      being accessed to sum up the lengths.
      
      We want to access the TFD here, which is the information for the
      hardware. We always only allocate 32 buffers for the cmd queue,
      but on newer hardware (using TFH) we can also allocate only a
      shorter hardware array, also only 32 TFDs. Prior to the TFH, we
      had to allocate a bigger TFD array but would make those point to
      a smaller set of buffers.
      
      Additionally, now max_tfd_queue_size is up to 65536, so we can
      access *way* out of bounds of a really only 32-entry array, so
      it crashes.
      
      Fix this by making the TFD index depend on which hardware we are
      using right now.
      
      While changing the calculation, also fix it to not use void ptr
      arithmetic, but cast to u8 * before.
      Signed-off-by: default avatarJohannes Berg <johannes.berg@intel.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      08326a97
    • Naftali Goldstein's avatar
      iwlwifi: mvm: fix race in sync rx queue notification · a2113cc4
      Naftali Goldstein authored
      Consider the following flow:
       1. Driver starts to sync the rx queues due to a delba.
          mvm->queue_sync_cookie=1.
          This rx-queues-sync is synchronous, so it doesn't increment the
          cookie until all rx queues handle the notification from FW.
       2. During this time, driver starts to sync rx queues due to nssn sync
          required.
          The cookie's value is still 1, but it doesn't matter since this
          rx-queue-sync is non-synchronous so in the notification handler the
          cookie is ignored.
          What _does_ matter is that this flow increments the cookie to 2
          immediately.
          Remember though that the FW won't start servicing this command until
          it's done with the previous one.
       3. FW is still handling the first command, so it sends a notification
          with internal_notif->sync=1, and internal_notif->cookie=0, which
          triggers a WARN_ONCE.
      
      The solution for this race is to only use the mvm->queue_sync_cookie in
      case of a synchronous sync-rx-queues. This way in step 2 the cookie's
      value won't change so we avoid the WARN.
      
      The commit in the "fixes" field is the first commit to introduce
      non-synchronous sending of this command to FW.
      
      Fixes: 3c514bf8 ("iwlwifi: mvm: add a loose synchronization of the NSSN across Rx queues")
      Signed-off-by: default avatarNaftali Goldstein <naftali.goldstein@intel.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      a2113cc4
    • Haim Dreyfuss's avatar
      iwlwifi: mvm: force single phy init · a4584729
      Haim Dreyfuss authored
      The PHY is initialized during device initialization, but devices with
      the tx_siso_diversity flag set need to send PHY_CONFIGURATION_CMD first,
      otherwise the PHY would be reinitialized, causing a SYSASSERT.
      
      To fix this, use a bit that tells the FW not to complete the PHY
      initialization before a PHY_CONFIGURATION_CMD is received.
      Signed-off-by: default avatarHaim Dreyfuss <haim.dreyfuss@intel.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      a4584729
    • Luca Coelho's avatar
      iwlwifi: fix ACPI table revision checks · 3ed83da3
      Luca Coelho authored
      We can't check for the ACPI table revision validity in the same if
      where we check if the package was read correctly, because we return
      PTR_ERR(pkg) and if the table is not valid but the pointer is, we
      would return a valid pointer as an error.  Fix that by moving the
      table checks to a separate if and return -EINVAL if it's not valid.
      Reported-by: default avatarDan Carpenter <dan.carpenter@oracle.com>
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      3ed83da3
    • Luca Coelho's avatar
      iwlwifi: don't access trans_cfg via cfg · 1fee35d0
      Luca Coelho authored
      We copy cfg->trans to trans->trans_cfg at the very beginning, so don't
      try to access it via cfg->trans anymore, because the cfg may be unset
      in later cases.
      Signed-off-by: default avatarLuca Coelho <luciano.coelho@intel.com>
      1fee35d0
  5. 08 Oct, 2019 1 commit
  6. 02 Oct, 2019 1 commit
  7. 30 Sep, 2019 17 commits
    • Linus Torvalds's avatar
      Linux 5.4-rc1 · 54ecb8f7
      Linus Torvalds authored
      54ecb8f7
    • Linus Torvalds's avatar
      Merge tag 'for-5.4-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux · bb48a591
      Linus Torvalds authored
      Pull btrfs fixes from David Sterba:
       "A bunch of fixes that accumulated in recent weeks, mostly material for
        stable.
      
        Summary:
      
         - fix for regression from 5.3 that prevents to use balance convert
           with single profile
      
         - qgroup fixes: rescan race, accounting leak with multiple writers,
           potential leak after io failure recovery
      
         - fix for use after free in relocation (reported by KASAN)
      
         - other error handling fixups"
      
      * tag 'for-5.4-rc1-tag' of git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux:
        btrfs: qgroup: Fix reserved data space leak if we have multiple reserve calls
        btrfs: qgroup: Fix the wrong target io_tree when freeing reserved data space
        btrfs: Fix a regression which we can't convert to SINGLE profile
        btrfs: relocation: fix use-after-free on dead relocation roots
        Btrfs: fix race setting up and completing qgroup rescan workers
        Btrfs: fix missing error return if writeback for extent buffer never started
        btrfs: adjust dirty_metadata_bytes after writeback failure of extent buffer
        Btrfs: fix selftests failure due to uninitialized i_mode in test inodes
      bb48a591
    • Linus Torvalds's avatar
      Merge tag 'csky-for-linus-5.4-rc1' of git://github.com/c-sky/csky-linux · 80b29b6b
      Linus Torvalds authored
      Pull csky updates from Guo Ren:
       "This round of csky subsystem just some fixups:
      
         - Fix mb() synchronization problem
      
         - Fix dma_alloc_coherent with PAGE_SO attribute
      
         - Fix cache_op failed when cross memory ZONEs
      
         - Optimize arch_sync_dma_for_cpu/device with dma_inv_range
      
         - Fix ioremap function losing
      
         - Fix arch_get_unmapped_area() implementation
      
         - Fix defer cache flush for 610
      
         - Support kernel non-aligned access
      
         - Fix 610 vipt cache flush mechanism
      
         - Fix add zero_fp fixup perf backtrace panic
      
         - Move static keyword to the front of declaration
      
         - Fix csky_pmu.max_period assignment
      
         - Use generic free_initrd_mem()
      
         - entry: Remove unneeded need_resched() loop"
      
      * tag 'csky-for-linus-5.4-rc1' of git://github.com/c-sky/csky-linux:
        csky: Move static keyword to the front of declaration
        csky: entry: Remove unneeded need_resched() loop
        csky: Fixup csky_pmu.max_period assignment
        csky: Fixup add zero_fp fixup perf backtrace panic
        csky: Use generic free_initrd_mem()
        csky: Fixup 610 vipt cache flush mechanism
        csky: Support kernel non-aligned access
        csky: Fixup defer cache flush for 610
        csky: Fixup arch_get_unmapped_area() implementation
        csky: Fixup ioremap function losing
        csky: Optimize arch_sync_dma_for_cpu/device with dma_inv_range
        csky/dma: Fixup cache_op failed when cross memory ZONEs
        csky: Fixup dma_alloc_coherent with PAGE_SO attribute
        csky: Fixup mb() synchronization problem
      80b29b6b
    • Linus Torvalds's avatar
      Merge tag 'armsoc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc · cef0aa0c
      Linus Torvalds authored
      Pull ARM SoC fixes from Olof Johansson:
       "A few fixes that have trickled in through the merge window:
      
         - Video fixes for OMAP due to panel-dpi driver removal
      
         - Clock fixes for OMAP that broke no-idle quirks + nfsroot on DRA7
      
         - Fixing arch version on ASpeed ast2500
      
         - Two fixes for reset handling on ARM SCMI"
      
      * tag 'armsoc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/soc/soc:
        ARM: aspeed: ast2500 is ARMv6K
        reset: reset-scmi: add missing handle initialisation
        firmware: arm_scmi: reset: fix reset_state assignment in scmi_domain_reset
        bus: ti-sysc: Remove unpaired sysc_clkdm_deny_idle()
        ARM: dts: logicpd-som-lv: Fix i2c2 and i2c3 Pin mux
        ARM: dts: am3517-evm: Fix missing video
        ARM: dts: logicpd-torpedo-baseboard: Fix missing video
        ARM: omap2plus_defconfig: Fix missing video
        bus: ti-sysc: Fix handling of invalid clocks
        bus: ti-sysc: Fix clock handling for no-idle quirks
      cef0aa0c
    • Linus Torvalds's avatar
      Merge tag 'trace-v5.4-3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace · cf4f493b
      Linus Torvalds authored
      Pull tracing fixes from Steven Rostedt:
       "A few more tracing fixes:
      
         - Fix a buffer overflow by checking nr_args correctly in probes
      
         - Fix a warning that is reported by clang
      
         - Fix a possible memory leak in error path of filter processing
      
         - Fix the selftest that checks for failures, but wasn't failing
      
         - Minor clean up on call site output of a memory trace event"
      
      * tag 'trace-v5.4-3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
        selftests/ftrace: Fix same probe error test
        mm, tracing: Print symbol name for call_site in trace events
        tracing: Have error path in predicate_parse() free its allocated memory
        tracing: Fix clang -Wint-in-bool-context warnings in IF_ASSIGN macro
        tracing/probe: Fix to check the difference of nr_args before adding probe
      cf4f493b
    • Linus Torvalds's avatar
      Merge tag 'mmc-v5.4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc · c710364f
      Linus Torvalds authored
      Pull more MMC updates from Ulf Hansson:
       "A couple more updates/fixes for MMC:
      
         - sdhci-pci: Add Genesys Logic GL975x support
      
         - sdhci-tegra: Recover loss in throughput for DMA
      
         - sdhci-of-esdhc: Fix DMA bug"
      
      * tag 'mmc-v5.4-2' of git://git.kernel.org/pub/scm/linux/kernel/git/ulfh/mmc:
        mmc: host: sdhci-pci: Add Genesys Logic GL975x support
        mmc: tegra: Implement ->set_dma_mask()
        mmc: sdhci: Let drivers define their DMA mask
        mmc: sdhci-of-esdhc: set DMA snooping based on DMA coherence
        mmc: sdhci: improve ADMA error reporting
      c710364f
    • Krzysztof Wilczynski's avatar
      csky: Move static keyword to the front of declaration · 9af032a3
      Krzysztof Wilczynski authored
      Move the static keyword to the front of declaration of
      csky_pmu_of_device_ids, and resolve the following compiler
      warning that can be seen when building with warnings
      enabled (W=1):
      
      arch/csky/kernel/perf_event.c:1340:1: warning:
        ‘static’ is not at beginning of declaration [-Wold-style-declaration]
      Signed-off-by: default avatarKrzysztof Wilczynski <kw@linux.com>
      Signed-off-by: default avatarGuo Ren <guoren@kernel.org>
      9af032a3
    • Valentin Schneider's avatar
      csky: entry: Remove unneeded need_resched() loop · a2139d3b
      Valentin Schneider authored
      Since the enabling and disabling of IRQs within preempt_schedule_irq()
      is contained in a need_resched() loop, we don't need the outer arch
      code loop.
      Signed-off-by: default avatarValentin Schneider <valentin.schneider@arm.com>
      Signed-off-by: default avatarGuo Ren <guoren@kernel.org>
      a2139d3b
    • Linus Torvalds's avatar
      Merge tag 'char-misc-5.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc · 97f9a3c4
      Linus Torvalds authored
      Pull Documentation/process update from Greg KH:
       "Here are two small Documentation/process/embargoed-hardware-issues.rst
        file updates that missed my previous char/misc pull request.
      
        The first one adds an Intel representative for the process, and the
        second one cleans up the text a bit more when it comes to how the
        disclosure rules work, as it was a bit confusing to some companies"
      
      * tag 'char-misc-5.4-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc:
        Documentation/process: Clarify disclosure rules
        Documentation/process: Volunteer as the ambassador for Intel
      97f9a3c4
    • Linus Torvalds's avatar
      Merge branch 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs · 1eb80d6f
      Linus Torvalds authored
      Pull more vfs updates from Al Viro:
       "A couple of misc patches"
      
      * 'work.misc' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
        afs dynroot: switch to simple_dir_operations
        fs/handle.c - fix up kerneldoc
      1eb80d6f
    • Linus Torvalds's avatar
      Merge tag '5.4-rc-smb3-fixes' of git://git.samba.org/sfrench/cifs-2.6 · 7edee522
      Linus Torvalds authored
      Pull more cifs updates from Steve French:
       "Fixes from the recent SMB3 Test events and Storage Developer
        Conference (held the last two weeks).
      
        Here are nine smb3 patches including an important patch for debugging
        traces with wireshark, with three patches marked for stable.
      
        Additional fixes from last week to better handle some newly discovered
        reparse points, and a fix the create/mkdir path for setting the mode
        more atomically (in SMB3 Create security descriptor context), and one
        for path name processing are still being tested so are not included
        here"
      
      * tag '5.4-rc-smb3-fixes' of git://git.samba.org/sfrench/cifs-2.6:
        CIFS: Fix oplock handling for SMB 2.1+ protocols
        smb3: missing ACL related flags
        smb3: pass mode bits into create calls
        smb3: Add missing reparse tags
        CIFS: fix max ea value size
        fs/cifs/sess.c: Remove set but not used variable 'capabilities'
        fs/cifs/smb2pdu.c: Make SMB2_notify_init static
        smb3: fix leak in "open on server" perf counter
        smb3: allow decryption keys to be dumped by admin for debugging
      7edee522
    • Mao Han's avatar
      csky: Fixup csky_pmu.max_period assignment · 3a09d8e2
      Mao Han authored
      The csky_pmu.max_period has type u64, and BIT() can only return
      32 bits unsigned long on C-SKY. The initialization for max_period
      will be incorrect when count_width is bigger than 32.
      
      Use BIT_ULL()
      Signed-off-by: default avatarMao Han <han_mao@c-sky.com>
      Signed-off-by: default avatarGuo Ren <ren_guo@c-sky.com>
      3a09d8e2
    • Guo Ren's avatar
      csky: Fixup add zero_fp fixup perf backtrace panic · 48ede51f
      Guo Ren authored
      We need set fp zero to let backtrace know the end. The patch fixup perf
      callchain panic problem, because backtrace didn't know what is the end
      of fp.
      Signed-off-by: default avatarGuo Ren <ren_guo@c-sky.com>
      Reported-by: default avatarMao Han <han_mao@c-sky.com>
      48ede51f
    • Mike Rapoport's avatar
      csky: Use generic free_initrd_mem() · fdbdcddc
      Mike Rapoport authored
      The csky implementation of free_initrd_mem() is an open-coded version of
      free_reserved_area() without poisoning.
      
      Remove it and make csky use the generic version of free_initrd_mem().
      Signed-off-by: default avatarMike Rapoport <rppt@linux.ibm.com>
      Signed-off-by: default avatarGuo Ren <guoren@kernel.org>
      fdbdcddc
    • Linus Torvalds's avatar
      Merge branch 'entropy' · 3f2dc279
      Linus Torvalds authored
      Merge active entropy generation updates.
      
      This is admittedly partly "for discussion".  We need to have a way
      forward for the boot time deadlocks where user space ends up waiting for
      more entropy, but no entropy is forthcoming because the system is
      entirely idle just waiting for something to happen.
      
      While this was triggered by what is arguably a user space bug with
      GDM/gnome-session asking for secure randomness during early boot, when
      they didn't even need any such truly secure thing, the issue ends up
      being that our "getrandom()" interface is prone to that kind of
      confusion, because people don't think very hard about whether they want
      to block for sufficient amounts of entropy.
      
      The approach here-in is to decide to not just passively wait for entropy
      to happen, but to start actively collecting it if it is missing.  This
      is not necessarily always possible, but if the architecture has a CPU
      cycle counter, there is a fair amount of noise in the exact timings of
      reasonably complex loads.
      
      We may end up tweaking the load and the entropy estimates, but this
      should be at least a reasonable starting point.
      
      As part of this, we also revert the revert of the ext4 IO pattern
      improvement that ended up triggering the reported lack of external
      entropy.
      
      * getrandom() active entropy waiting:
        Revert "Revert "ext4: make __ext4_get_inode_loc plug""
        random: try to actively add entropy rather than passively wait for it
      3f2dc279
    • Linus Torvalds's avatar
      Revert "Revert "ext4: make __ext4_get_inode_loc plug"" · 02f03c42
      Linus Torvalds authored
      This reverts commit 72dbcf72.
      
      Instead of waiting forever for entropy that may just not happen, we now
      try to actively generate entropy when required, and are thus hopefully
      avoiding the problem that caused the nice ext4 IO pattern fix to be
      reverted.
      
      So revert the revert.
      
      Cc: Ahmed S. Darwish <darwish.07@gmail.com>
      Cc: Ted Ts'o <tytso@mit.edu>
      Cc: Willy Tarreau <w@1wt.eu>
      Cc: Alexander E. Patrakov <patrakov@gmail.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      02f03c42
    • Linus Torvalds's avatar
      random: try to actively add entropy rather than passively wait for it · 50ee7529
      Linus Torvalds authored
      For 5.3 we had to revert a nice ext4 IO pattern improvement, because it
      caused a bootup regression due to lack of entropy at bootup together
      with arguably broken user space that was asking for secure random
      numbers when it really didn't need to.
      
      See commit 72dbcf72 (Revert "ext4: make __ext4_get_inode_loc plug").
      
      This aims to solve the issue by actively generating entropy noise using
      the CPU cycle counter when waiting for the random number generator to
      initialize.  This only works when you have a high-frequency time stamp
      counter available, but that's the case on all modern x86 CPU's, and on
      most other modern CPU's too.
      
      What we do is to generate jitter entropy from the CPU cycle counter
      under a somewhat complex load: calling the scheduler while also
      guaranteeing a certain amount of timing noise by also triggering a
      timer.
      
      I'm sure we can tweak this, and that people will want to look at other
      alternatives, but there's been a number of papers written on jitter
      entropy, and this should really be fairly conservative by crediting one
      bit of entropy for every timer-induced jump in the cycle counter.  Not
      because the timer itself would be all that unpredictable, but because
      the interaction between the timer and the loop is going to be.
      
      Even if (and perhaps particularly if) the timer actually happens on
      another CPU, the cacheline interaction between the loop that reads the
      cycle counter and the timer itself firing is going to add perturbations
      to the cycle counter values that get mixed into the entropy pool.
      
      As Thomas pointed out, with a modern out-of-order CPU, even quite simple
      loops show a fair amount of hard-to-predict timing variability even in
      the absense of external interrupts.  But this tries to take that further
      by actually having a fairly complex interaction.
      
      This is not going to solve the entropy issue for architectures that have
      no CPU cycle counter, but it's not clear how (and if) that is solvable,
      and the hardware in question is largely starting to be irrelevant.  And
      by doing this we can at least avoid some of the even more contentious
      approaches (like making the entropy waiting time out in order to avoid
      the possibly unbounded waiting).
      
      Cc: Ahmed Darwish <darwish.07@gmail.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Theodore Ts'o <tytso@mit.edu>
      Cc: Nicholas Mc Guire <hofrat@opentech.at>
      Cc: Andy Lutomirski <luto@kernel.org>
      Cc: Kees Cook <keescook@chromium.org>
      Cc: Willy Tarreau <w@1wt.eu>
      Cc: Alexander E. Patrakov <patrakov@gmail.com>
      Cc: Lennart Poettering <mzxreary@0pointer.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      50ee7529