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Dexuan Cui fff7b5e6ee x86/hyperv: Initialize clockevents after LAPIC is initialized 
With commit 4df4cb9e99, the Hyper-V direct-mode STIMER is actually
initialized before LAPIC is initialized: see

  apic_intr_mode_init()

    x86_platform.apic_post_init()
      hyperv_init()
        hv_stimer_alloc()

    apic_bsp_setup()
      setup_local_APIC()

setup_local_APIC() temporarily disables LAPIC, initializes it and
re-eanble it.  The direct-mode STIMER depends on LAPIC, and when it's
registered, it can be programmed immediately and the timer can fire
very soon:

  hv_stimer_init
    clockevents_config_and_register
      clockevents_register_device
        tick_check_new_device
          tick_setup_device
            tick_setup_periodic(), tick_setup_oneshot()
              clockevents_program_event

When the timer fires in the hypervisor, if the LAPIC is in the
disabled state, new versions of Hyper-V ignore the event and don't inject
the timer interrupt into the VM, and hence the VM hangs when it boots.

Note: when the VM starts/reboots, the LAPIC is pre-enabled by the
firmware, so the window of LAPIC being temporarily disabled is pretty
small, and the issue can only happen once out of 100~200 reboots for
a 40-vCPU VM on one dev host, and on another host the issue doesn't
reproduce after 2000 reboots.

The issue is more noticeable for kdump/kexec, because the LAPIC is
disabled by the first kernel, and stays disabled until the kdump/kexec
kernel enables it. This is especially an issue to a Generation-2 VM
(for which Hyper-V doesn't emulate the PIT timer) when CONFIG_HZ=1000
(rather than CONFIG_HZ=250) is used.

Fix the issue by moving hv_stimer_alloc() to a later place where the
LAPIC timer is initialized.

Fixes: 4df4cb9e99 ("x86/hyperv: Initialize clockevents earlier in CPU onlining")
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by:  Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20210116223136.13892-1-decui@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
 		2021-01-17 15:20:50 +00:00
Documentation A small set of late-arriving, small documentation fixes. 2020-12-24 14:20:33 -08:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
arch x86/hyperv: Initialize clockevents after LAPIC is initialized 2021-01-17 15:20:50 +00:00
block SCSI fixes on 20210101 2021-01-01 12:58:07 -08:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto crypto: aegis128 - avoid spurious references crypto_aegis128_update_simd 2020-12-04 18:16:53 +11:00
drivers x86/hyperv: Fix kexec panic/hang issues 2021-01-05 17:52:04 +00:00
fs block-5.11-2021-01-01 2021-01-01 12:49:09 -08:00
include SCSI fixes on 20210101 2021-01-01 12:58:07 -08:00
init kasan, arm64: only use kasan_depth for software modes 2020-12-22 12:55:07 -08:00
ipc Merge branch 'akpm' (patches from Andrew) 2020-12-15 12:53:37 -08:00
kernel io_uring-5.11-2021-01-01 2021-01-01 12:29:49 -08:00
lib zlib: move EXPORT_SYMBOL() and MODULE_LICENSE() out of dfltcc_syms.c 2020-12-29 15:36:49 -08:00
mm mm: slub: call account_slab_page() after slab page initialization 2020-12-29 15:36:49 -08:00
net libceph: align session_key and con_secret to 16 bytes 2020-12-28 20:34:33 +01:00
samples ARM: SoC drivers for v5.11 2020-12-16 16:38:41 -08:00
scripts depmod: handle the case of /sbin/depmod without /sbin in PATH 2021-01-01 12:26:39 -08:00
security Provide a fix for the incorrect handling of privilege 2020-12-24 14:08:43 -08:00
sound sound fixes for 5.11-rc1 2020-12-23 15:11:08 -08:00
tools selftests/vm: fix building protection keys test 2020-12-29 15:36:49 -08:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt ARM: 2020-12-20 10:44:05 -08:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap RDMA 5.11 pull request 2020-12-16 13:42:26 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-11 22:29:38 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Merge branches 'pm-cpufreq' and 'pm-cpuidle' 2021-01-02 10:16:32 +01:00
Makefile Linux 5.11-rc2 2021-01-03 15:55:30 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.