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linux/arch/powerpc/kvm/Kconfig
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

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# SPDX-License-Identifier: GPL-2.0
#
# KVM configuration
#
source "virt/kvm/Kconfig"
menuconfig VIRTUALIZATION
bool "Virtualization"
help
Say Y here to get to see options for using your Linux host to run
other operating systems inside virtual machines (guests).
This option alone does not add any kernel code.
If you say N, all options in this submenu will be skipped and
disabled.
if VIRTUALIZATION
config KVM
bool
select KVM_COMMON
select KVM_VFIO
select HAVE_KVM_IRQ_BYPASS
select VIRT_XFER_TO_GUEST_WORK
config KVM_BOOK3S_HANDLER
bool
config KVM_BOOK3S_32_HANDLER
bool
select KVM_BOOK3S_HANDLER
select KVM_MMIO
config KVM_BOOK3S_64_HANDLER
bool
select KVM_BOOK3S_HANDLER
config KVM_BOOK3S_PR_POSSIBLE
bool
select KVM_MMIO
config KVM_BOOK3S_HV_POSSIBLE
bool
config KVM_BOOK3S_32
tristate "KVM support for PowerPC book3s_32 processors"
depends on PPC_BOOK3S_32 && !SMP && !PTE_64BIT
depends on !CONTEXT_TRACKING_USER
select KVM
select KVM_BOOK3S_32_HANDLER
select KVM_BOOK3S_PR_POSSIBLE
select PPC_FPU
help
Support running unmodified book3s_32 guest kernels
in virtual machines on book3s_32 host processors.
This module provides access to the hardware capabilities through
a character device node named /dev/kvm.
If unsure, say N.
config KVM_BOOK3S_64
tristate "KVM support for PowerPC book3s_64 processors"
depends on PPC_BOOK3S_64
select KVM_BOOK3S_64_HANDLER
select KVM
select KVM_BOOK3S_PR_POSSIBLE if !KVM_BOOK3S_HV_POSSIBLE
select PPC_64S_HASH_MMU
select SPAPR_TCE_IOMMU if IOMMU_SUPPORT && (PPC_PSERIES || PPC_POWERNV)
help
Support running unmodified book3s_64 and book3s_32 guest kernels
in virtual machines on book3s_64 host processors.
This module provides access to the hardware capabilities through
a character device node named /dev/kvm.
If unsure, say N.
config KVM_BOOK3S_64_HV
tristate "KVM for POWER7 and later using hypervisor mode in host"
depends on KVM_BOOK3S_64 && PPC_POWERNV
select KVM_BOOK3S_HV_POSSIBLE
select KVM_BOOK3S_HV_PMU
select CMA
help
Support running unmodified book3s_64 guest kernels in
virtual machines on POWER7 and newer processors that have
hypervisor mode available to the host.
If you say Y here, KVM will use the hardware virtualization
facilities of POWER7 (and later) processors, meaning that
guest operating systems will run at full hardware speed
using supervisor and user modes. However, this also means
that KVM is not usable under PowerVM (pHyp), is only usable
on POWER7 or later processors, and cannot emulate a
different processor from the host processor.
If unsure, say N.
config KVM_BOOK3S_64_PR
tristate "KVM support without using hypervisor mode in host"
depends on KVM_BOOK3S_64
depends on !CONTEXT_TRACKING_USER
select KVM_BOOK3S_PR_POSSIBLE
help
Support running guest kernels in virtual machines on processors
without using hypervisor mode in the host, by running the
guest in user mode (problem state) and emulating all
privileged instructions and registers.
This is only available for hash MMU mode and only supports
guests that use hash MMU mode.
This is not as fast as using hypervisor mode, but works on
machines where hypervisor mode is not available or not usable,
and can emulate processors that are different from the host
processor, including emulating 32-bit processors on a 64-bit
host.
Selecting this option will cause the SCV facility to be
disabled when the kernel is booted on the pseries platform in
hash MMU mode (regardless of PR VMs running). When any PR VMs
are running, "AIL" mode is disabled which may slow interrupts
and system calls on the host.
config KVM_BOOK3S_HV_EXIT_TIMING
bool
config KVM_BOOK3S_HV_P9_TIMING
bool "Detailed timing for the P9 entry point"
select KVM_BOOK3S_HV_EXIT_TIMING
depends on KVM_BOOK3S_HV_POSSIBLE && DEBUG_FS
help
Calculate time taken for each vcpu during vcpu entry and
exit, time spent inside the guest and time spent handling
hypercalls and page faults. The total, minimum and maximum
times in nanoseconds together with the number of executions
are reported in debugfs in kvm/vm#/vcpu#/timings.
If unsure, say N.
config KVM_BOOK3S_HV_P8_TIMING
bool "Detailed timing for hypervisor real-mode code (for POWER8)"
select KVM_BOOK3S_HV_EXIT_TIMING
depends on KVM_BOOK3S_HV_POSSIBLE && DEBUG_FS && !KVM_BOOK3S_HV_P9_TIMING
help
Calculate time taken for each vcpu in the real-mode guest entry,
exit, and interrupt handling code, plus time spent in the guest
and in nap mode due to idle (cede) while other threads are still
in the guest. The total, minimum and maximum times in nanoseconds
together with the number of executions are reported in debugfs in
kvm/vm#/vcpu#/timings. The overhead is of the order of 30 - 40
ns per exit on POWER8.
If unsure, say N.
config KVM_BOOK3S_HV_NESTED_PMU_WORKAROUND
bool "Nested L0 host workaround for L1 KVM host PMU handling bug" if EXPERT
depends on KVM_BOOK3S_HV_POSSIBLE
default !EXPERT
help
Old nested HV capable Linux guests have a bug where they don't
reflect the PMU in-use status of their L2 guest to the L0 host
while the L2 PMU registers are live. This can result in loss
of L2 PMU register state, causing perf to not work correctly in
L2 guests.
Selecting this option for the L0 host implements a workaround for
those buggy L1s which saves the L2 state, at the cost of performance
in all nested-capable guest entry/exit.
config KVM_BOOK3S_HV_PMU
tristate "Hypervisor Perf events for KVM Book3s-HV"
depends on KVM_BOOK3S_64_HV
help
Enable Book3s-HV Hypervisor Perf events PMU named 'kvm-hv'. These
Perf events give an overview of hypervisor performance overall
instead of a specific guests. Currently the PMU reports
L0-Hypervisor stats on a kvm-hv enabled PSeries LPAR like:
* Total/Used Guest-Heap
* Total/Used Guest Page-table Memory
* Total amount of Guest Page-table Memory reclaimed
config KVM_BOOKE_HV
bool
config KVM_EXIT_TIMING
bool "Detailed exit timing"
depends on KVM_E500V2 || KVM_E500MC
help
Calculate elapsed time for every exit/enter cycle. A per-vcpu
report is available in debugfs kvm/vm#_vcpu#_timing.
The overhead is relatively small, however it is not recommended for
production environments.
If unsure, say N.
config KVM_E500V2
bool "KVM support for PowerPC E500v2 processors"
depends on PPC_E500 && !PPC_E500MC
depends on !CONTEXT_TRACKING_USER
select KVM
select KVM_MMIO
help
Support running unmodified E500 guest kernels in virtual machines on
E500v2 host processors.
This module provides access to the hardware capabilities through
a character device node named /dev/kvm.
If unsure, say N.
config KVM_E500MC
bool "KVM support for PowerPC E500MC/E5500/E6500 processors"
depends on PPC_E500MC
depends on !CONTEXT_TRACKING_USER
select KVM
select KVM_MMIO
select KVM_BOOKE_HV
help
Support running unmodified E500MC/E5500/E6500 guest kernels in
virtual machines on E500MC/E5500/E6500 host processors.
This module provides access to the hardware capabilities through
a character device node named /dev/kvm.
If unsure, say N.
config KVM_MPIC
bool "KVM in-kernel MPIC emulation"
depends on KVM && PPC_E500
select HAVE_KVM_IRQCHIP
select HAVE_KVM_IRQ_ROUTING
select HAVE_KVM_MSI
help
Enable support for emulating MPIC devices inside the
host kernel, rather than relying on userspace to emulate.
Currently, support is limited to certain versions of
Freescale's MPIC implementation.
config KVM_XICS
bool "KVM in-kernel XICS emulation"
depends on KVM_BOOK3S_64 && !KVM_MPIC
select HAVE_KVM_IRQCHIP
default y
help
Include support for the XICS (eXternal Interrupt Controller
Specification) interrupt controller architecture used on
IBM POWER (pSeries) servers.
config KVM_XIVE
bool
default y
depends on KVM_XICS && PPC_XIVE_NATIVE && KVM_BOOK3S_HV_POSSIBLE
endif # VIRTUALIZATION
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