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Linux kernel for uConsole
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Heyi Guo ff232a4756 irqchip/gic-v3-its: Fix command queue pointer comparison bug 
[ Upstream commit a050fa5476 ]

When we run several VMs with PCI passthrough and GICv4 enabled, not
pinning vCPUs, we will occasionally see below warnings in dmesg:

ITS queue timeout (65440 65504 480)
ITS cmd its_build_vmovp_cmd failed

The reason for the above issue is that in BUILD_SINGLE_CMD_FUNC:
1. Post the write command.
2. Release the lock.
3. Start to read GITS_CREADR to get the reader pointer.
4. Compare the reader pointer to the target pointer.
5. If reader pointer does not reach the target, sleep 1us and continue
to try.

If we have several processors running the above concurrently, other
CPUs will post write commands while the 1st CPU is waiting the
completion. So we may have below issue:

phase 1:
---rd_idx-----from_idx-----to_idx--0---------

wait 1us:

phase 2:
--------------from_idx-----to_idx--0-rd_idx--

That is the rd_idx may fly ahead of to_idx, and if in case to_idx is
near the wrap point, rd_idx will wrap around. So the below condition
will not be met even after 1s:

if (from_idx < to_idx && rd_idx >= to_idx)

There is another theoretical issue. For a slow and busy ITS, the
initial rd_idx may fall behind from_idx a lot, just as below:

---rd_idx---0--from_idx-----to_idx-----------

This will cause the wait function exit too early.

Actually, it does not make much sense to use from_idx to judge if
to_idx is wrapped, but we need a initial rd_idx when lock is still
acquired, and it can be used to judge whether to_idx is wrapped and
the current rd_idx is wrapped.

We switch to a method of calculating the delta of two adjacent reads
and accumulating it to get the sum, so that we can get the real rd_idx
from the wrapped value even when the queue is almost full.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Heyi Guo <guoheyi@huawei.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2019-07-21 09:03:03 +02:00
arch MIPS: Remove superfluous check for __linux__ 2019-07-14 08:11:21 +02:00
block block, bfq: NULL out the bic when it's no longer valid 2019-07-14 08:11:17 +02:00
certs export.h: remove VMLINUX_SYMBOL() and VMLINUX_SYMBOL_STR() 2018-08-22 23:21:44 +09:00
crypto crypto: cryptd - Fix skcipher instance memory leak 2019-07-10 09:53:41 +02:00
Documentation Documentation/admin: Remove the vsyscall=native documentation 2019-07-14 08:11:18 +02:00
drivers irqchip/gic-v3-its: Fix command queue pointer comparison bug 2019-07-21 09:03:03 +02:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs udf: Fix incorrect final NOT_ALLOCATED (hole) extent length 2019-07-14 08:11:16 +02:00
include drivers: base: cacheinfo: Ensure cpu hotplug work is done before Intel RDT 2019-07-21 09:03:03 +02:00
init initramfs: free initrd memory if opening /initrd.image fails 2019-06-15 11:54:01 +02:00
ipc ipc: prevent lockup on alloc_msg and free_msg 2019-06-15 11:54:00 +02:00
kernel bpf, devmap: Add missing RCU read lock on flush 2019-07-14 08:11:11 +02:00
lib lib/mpi: Fix karactx leak in mpi_powm 2019-07-10 09:53:42 +02:00
LICENSES LICENSES: Remove CC-BY-SA-4.0 license text 2018-10-18 11:28:50 +02:00
mm mm/vmscan.c: prevent useless kswapd loops 2019-07-10 09:53:44 +02:00
net net :sunrpc :clnt :Fix xps refcount imbalance on the error path 2019-07-14 08:11:15 +02:00
samples samples, bpf: suppress compiler warning 2019-07-14 08:11:04 +02:00
scripts scripts/decode_stacktrace.sh: prefix addr2line with $CROSS_COMPILE 2019-07-10 09:53:39 +02:00
security apparmor: enforce nullbyte at end of tag string 2019-06-25 11:35:54 +08:00
sound ALSA: hda/realtek - Headphone Mic can't record after S3 2019-07-14 08:11:16 +02:00
tools perf pmu: Fix uncore PMU alias list for ARM64 2019-07-14 08:11:17 +02:00
usr initramfs: move gen_initramfs_list.sh from scripts/ to usr/ 2018-08-22 23:21:44 +09:00
virt KVM: arm/arm64: vgic: Fix kvm_device leak in vgic_its_destroy 2019-07-14 08:11:10 +02:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap libnvdimm-for-4.19_misc 2018-08-25 18:13:10 -07:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS platform/x86: Add Intel AtomISP2 dummy / power-management driver 2019-04-20 09:16:02 +02:00
Makefile Linux 4.19.59 2019-07-14 08:11:23 +02:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -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.
See Documentation/00-INDEX for a list of what is contained in each file.

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.