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Thomas Gleixner 0e245256e3 x86/ioapic: Ignore IRQ2 again 
commit a501b048a9 upstream.

Vitaly ran into an issue with hotplugging CPU0 on an Amazon instance where
the matrix allocator claimed to be out of vectors. He analyzed it down to
the point that IRQ2, the PIC cascade interrupt, which is supposed to be not
ever routed to the IO/APIC ended up having an interrupt vector assigned
which got moved during unplug of CPU0.

The underlying issue is that IRQ2 for various reasons (see commit
af174783b9 ("x86: I/O APIC: Never configure IRQ2" for details) is treated
as a reserved system vector by the vector core code and is not accounted as
a regular vector. The Amazon BIOS has an routing entry of pin2 to IRQ2
which causes the IO/APIC setup to claim that interrupt which is granted by
the vector domain because there is no sanity check. As a consequence the
allocation counter of CPU0 underflows which causes a subsequent unplug to
fail with:

  [ ... ] CPU 0 has 4294967295 vectors, 589 available. Cannot disable CPU

There is another sanity check missing in the matrix allocator, but the
underlying root cause is that the IO/APIC code lost the IRQ2 ignore logic
during the conversion to irqdomains.

For almost 6 years nobody complained about this wreckage, which might
indicate that this requirement could be lifted, but for any system which
actually has a PIC IRQ2 is unusable by design so any routing entry has no
effect and the interrupt cannot be connected to a device anyway.

Due to that and due to history biased paranoia reasons restore the IRQ2
ignore logic and treat it as non existent despite a routing entry claiming
otherwise.

Fixes: d32932d02e ("x86/irq: Convert IOAPIC to use hierarchical irqdomain interfaces")
Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210318192819.636943062@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2021-03-25 09:04:16 +01:00
arch x86/ioapic: Ignore IRQ2 again 2021-03-25 09:04:16 +01:00
block block: Discard page cache of zone reset target range 2021-03-17 17:06:27 +01:00
certs certs: Fix blacklist flag type confusion 2021-03-04 11:37:59 +01:00
crypto crypto: mips/poly1305 - enable for all MIPS processors 2021-03-17 17:06:10 +01:00
Documentation scsi: libsas: Introduce a _gfp() variant of event notifiers 2021-03-25 09:04:11 +01:00
drivers PCI: rpadlpar: Fix potential drc_name corruption in store functions 2021-03-25 09:04:16 +01:00
fs gfs2: bypass signal_our_withdraw if no journal 2021-03-25 09:04:14 +01:00
include usb-storage: Add quirk to defeat Kindle's automatic unload 2021-03-25 09:04:14 +01:00
init kgdb: fix to kill breakpoints on initmem after boot 2021-03-04 11:38:46 +01:00
ipc ipc: adjust proc_ipc_sem_dointvec definition to match prototype 2020-09-05 12:14:29 -07:00
kernel module: harden ELF info handling 2021-03-25 09:04:11 +01:00
lib kasan: fix memory corruption in kasan_bitops_tags test 2021-03-17 17:06:25 +01:00
LICENSES LICENSES/deprecated: add Zlib license text 2020-09-16 14:33:49 +02:00
mm mm/page_alloc.c: refactor initialization of struct page for holes in memory layout 2021-03-17 17:06:37 +01:00
net net/qrtr: fix __netdev_alloc_skb call 2021-03-25 09:04:09 +01:00
samples samples, bpf: Add missing munmap in xdpsock 2021-03-17 17:06:12 +01:00
scripts ftrace: Have recordmcount use w8 to read relp->r_info in arm64_is_fake_mcount 2021-03-09 11:11:14 +01:00
security Revert 95ebabde38 ("capabilities: Don't allow writing ambiguous v3 file capabilities") 2021-03-17 17:06:27 +01:00
sound ALSA: usb-audio: Fix unintentional sign extension issue 2021-03-25 09:04:07 +01:00
tools bpf, selftests: Fix up some test_verifier cases for unprivileged 2021-03-20 10:43:43 +01:00
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 KVM: Use kvm_pfn_t for local PFN variable in hva_to_pfn_remapped() 2021-02-26 10:13:01 +01:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig
.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 mailmap: add two more addresses of Uwe Kleine-König 2020-12-06 10:19:07 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Jason Cooper to CREDITS 2020-11-30 10:20:34 +01:00
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 git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-12-10 15:30:13 -08:00
Makefile kbuild: Fix <linux/version.h> for empty SUBLEVEL or PATCHLEVEL again 2021-03-25 09:04:09 +01:00
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.