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Vishal Chourasia 12013e3d46 KVM: powerpc: Use generic xfer to guest work function
Since commit 2cd571245b ("sched/fair: Add related data structure for
task based throttle") in v6.18, CFS bandwidth throttling no longer
dequeues a task directly; it queues task_work via TWA_RESUME and sets
TIF_NOTIFY_RESUME, relying on that work running before the task returns
to guest/user mode. The powerpc KVM run loops only checked for reschedule
and signals, never TIF_NOTIFY_RESUME, so the deferred throttle never ran
while a vCPU stayed in the run loop: a CPU-bound guest that rarely exits
to userspace ran far past its cpu.max quota and then appeared frozen for
minutes while the accrued throttle debt was repaid.

Use the generic infrastructure to check for and handle pending work
before transitioning into guest mode, replacing the open-coded
need_resched() and cond_resched() checks in the Book3S HV run loops and
in the common kvmppc_prepare_to_enter() used by the Book3S PR and BookE
run loops. The redundant signal_pending() recheck (and its sigpend label)
in kvmhv_run_single_vcpu() is also dropped, as
xfer_to_guest_mode_work_pending() is a superset of it.

This picks up handling for TIF_NOTIFY_RESUME, which was previously
ignored, meaning task work will now be correctly handled on every
guest re-entry.

Selecting VIRT_XFER_TO_GUEST_WORK disables RCU's last-resort self-IPI
fallback for vCPU tasks (see rcu_irq_work_resched()), which on
nohz_full CPUs was what forced a reschedule for deferred rcuog wakeups
queued right before guest entry. Take over that obligation the same way
x86 and s390 do: call xfer_to_guest_mode_prepare() with IRQs disabled
immediately before the final xfer_to_guest_mode_work_pending() check at
each guest-entry gate (kvmhv_run_single_vcpu(), kvmppc_run_core() and
kvmppc_prepare_to_enter()).

In kvmppc_prepare_to_enter(), IRQs are now disabled with
local_irq_disable() before hard_irq_disable(): on 32-bit,
hard_irq_disable() is a raw MSR[EE] clear that bypasses the
lockdep/irq-tracing state, and the strict xfer_to_guest_mode helpers
assert that IRQs are seen as disabled. This also allows upgrading the
racy __xfer_to_guest_mode_work_pending() check to the asserting
variant, as this loop is the terminal gate for the PR and BookE paths.

In kvmhv_run_single_vcpu(), the -EINTR exit and the pre-existing
kvmhv_setup_mmu() failure exit now leave via the done label instead of
returning directly, keeping the run_vcpu enter/exit tracepoints
balanced and vcpu->arch.ret consistent with the returned value.

In kvmppc_prepare_to_enter() the generic helper accounts the signal exit
(vcpu->stat.signal_exits and KVM_EXIT_INTR) but does not set the exit
type, so kvmppc_set_exit_type(SIGNAL_EXITS) is retained on the signal
path to preserve the E500 CONFIG_KVM_EXIT_TIMING histogram; it is a no-op
otherwise.

Signed-off-by: Vishal Chourasia <vishalc@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20260709092140.1753715-4-vishalc@linux.ibm.com
2026-07-31 16:58:51 +05:30
arch KVM: powerpc: Use generic xfer to guest work function 2026-07-31 16:58:51 +05:30
block block: fix aligning of bounced dio read bios 2026-07-16 06:11:37 -06:00
certs treewide: fix indentation and whitespace in Kconfig files 2026-05-28 21:24:42 -07:00
crypto crypto: aes - Fix conditions for selecting MAC dependencies 2026-07-09 11:06:22 -04:00
Documentation spi: Fixes for v7.2 2026-07-26 12:13:42 -07:00
drivers spi: Fixes for v7.2 2026-07-26 12:13:42 -07:00
fs vfs-7.2-rc5.fixes 2026-07-26 12:22:57 -07:00
include vfs-7.2-rc5.fixes 2026-07-26 12:22:57 -07:00
init rust: allow suspicious_runtime_symbol_definitions lint for Rust >= 1.98 2026-06-29 13:02:15 +02:00
io_uring io_uring-7.2-20260724 2026-07-24 19:58:03 -07:00
ipc kernel-7.2-rc1.misc 2026-06-15 03:05:50 +05:30
kernel tracing fix for 7.2: 2026-07-26 09:15:59 -07:00
lib slab fixes for 7.2-rc4 2026-07-24 07:28:35 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm vfs-7.2-rc5.fixes 2026-07-26 12:22:57 -07:00
net BPF fixes: 2026-07-24 19:31:12 -07:00
rust powerpc: Enable Rust for ppc64le 2026-07-31 16:57:48 +05:30
samples tracing fixes for 7.2: 2026-07-12 09:46:37 -07:00
scripts rust/powerpc: Set min rustc version for powerpc 2026-07-31 16:57:48 +05:30
security selinux/stable-7.2 PR 20260717 2026-07-17 11:04:46 -07:00
sound ALSA: hda/realtek - Add quirk for Dell Pro QC1255 2026-07-21 09:55:17 +02:00
tools vfs-7.2-rc5.fixes 2026-07-26 12:22:57 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt KVM/arm64 fixes for 7.2, take #2 2026-07-15 12:13:30 +02:00
.clang-format clang-format: fix formatting of guard() and scoped_guard() statements 2026-05-28 21:24:41 -07:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add myself 2026-04-02 16:48:25 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore SPDX patches for 7.2-rc1 2026-06-22 12:06:22 -07:00
.mailmap drm fixes for 7.2-rc5 2026-07-24 14:11:53 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING
CREDITS CREDITS: Add Wolfram Sang 2026-07-14 16:34:04 +02:00
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Char/Misc driver fixes for 7.2-rc5 2026-07-26 10:47:58 -07:00
Makefile Linux 7.2-rc5 2026-07-26 14:45:48 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -07:00

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

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst