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Message-ID: <e17627fb-283e-dd42-94c1-f89dea167577@redhat.com>
Date: Wed, 29 Mar 2023 13:52:07 +0800
From: Shaoqin Huang <shahuang@...hat.com>
To: James Morse <james.morse@....com>, linux-pm@...r.kernel.org,
loongarch@...ts.linux.dev, kvmarm@...ts.linux.dev,
kvm@...r.kernel.org, linux-acpi@...r.kernel.org,
linux-arch@...r.kernel.org, linux-ia64@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
x86@...nel.org
Cc: Marc Zyngier <maz@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Sudeep Holla <sudeep.holla@....com>,
Borislav Petkov <bp@...en8.de>, H Peter Anvin <hpa@...or.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
Huacai Chen <chenhuacai@...nel.org>,
Suzuki K Poulose <suzuki.poulose@....com>,
Oliver Upton <oliver.upton@...ux.dev>,
Len Brown <lenb@...nel.org>,
Rafael Wysocki <rafael@...nel.org>,
WANG Xuerui <kernel@...0n.name>,
Salil Mehta <salil.mehta@...wei.com>,
Russell King <linux@...linux.org.uk>,
Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [RFC PATCH 00/32] ACPI/arm64: add support for virtual cpuhotplug
Hi James,
On 2/3/23 21:50, James Morse wrote:
> Hello!
>
> This series adds what looks like cpuhotplug support to arm64 for use in
> virtual machines. It does this by moving the cpu_register() calls for
> architectures that support ACPI out of the arch code by using
> GENERIC_CPU_DEVICES, then into the ACPI processor driver.
>
> The kubernetes folk really want to be able to add CPUs to an existing VM,
> in exactly the same way they do on x86. The use-case is pre-booting guests
> with one CPU, then adding the number that were actually needed when the
> workload is provisioned.
>
> Wait? Doesn't arm64 support cpuhotplug already!?
> In the arm world, cpuhotplug gets used to mean removing the power from a CPU.
> The CPU is offline, and remains present. For x86, and ACPI, cpuhotplug
> has the additional step of physically removing the CPU, so that it isn't
> present anymore.
>
> Arm64 doesn't support this, and can't support it: CPUs are really a slice
> of the SoC, and there is not enough information in the existing ACPI tables
> to describe which bits of the slice also got removed. Without a reference
> machine: adding this support to the spec is a wild goose chase.
>
> Critically: everything described in the firmware tables must remain present.
>
> For a virtual machine this is easy as all the other bits of 'virtual SoC'
> are emulated, so they can (and do) remain present when a vCPU is 'removed'.
>
> On a system that supports cpuhotplug the MADT has to describe every possible
> CPU at boot. Under KVM, the vGIC needs to know about every possible vCPU before
> the guest is started.
> With these constraints, virtual-cpuhotplug is really just a hypervisor/firmware
> policy about which CPUs can be brought online.
>
> This series adds support for virtual-cpuhotplug as exactly that: firmware
> policy. This may even work on a physical machine too; for a guest the part of
> firmware is played by the VMM. (typically Qemu).
>
> PSCI support is modified to return 'DENIED' if the CPU can't be brought
> online/enabled yet. The CPU object's _STA method's enabled bit is used to
> indicate firmware's current disposition. If the CPU has its enabled bit clear,
> it will not be registered with sysfs, and attempts to bring it online will
> fail. The notifications that _STA has changed its value then work in the same
> way as physical hotplug, and firmware can cause the CPU to be registered some
> time later, allowing it to be brought online.
>
> This creates something that looks like cpuhotplug to user-space, as the sysfs
> files appear and disappear, and the udev notifications look the same.
>
> One notable difference is the CPU present mask, which is exposed via sysfs.
> Because the CPUs remain present throughout, they can still be seen in that mask.
> This value does get used by webbrowsers to estimate the number of CPUs
> as the CPU online mask is constantly changed on mobile phones.
>
> Linux is tolerant of PSCI returning errors, as its always been allowed to do
> that. To avoid confusing OS that can't tolerate this, we needed an additional
> bit in the MADT GICC flags. This series copies ACPI_MADT_ONLINE_CAPABLE, which
> appears to be for this purpose, but calls it ACPI_MADT_GICC_CPU_CAPABLE as it
> has a different bit position in the GICC.
>
> This code is unconditionally enabled for all ACPI architectures.
> If there are problems with firmware tables on some devices, the CPUs will
> already be online by the time the acpi_processor_make_enabled() is called.
> A mismatch here causes a firmware-bug message and kernel taint. This should
> only affect people with broken firmware who also boot with maxcpus=1, and
> bring CPUs online later.
>
> I had a go at switching the remaining architectures over to GENERIC_CPU_DEVICES,
> so that the Kconfig symbol can be removed, but I got stuck with powerpc
> and s390.
>
>
> The first patch has already been posted as a fix here:
> https://www.spinics.net/lists/linux-ia64/msg21920.html
> I've only build tested Loongarch and ia64.
>
>
> If folk want to play along at home, you'll need a copy of Qemu that supports this.
> https://github.com/salil-mehta/qemu.git salil/virt-cpuhp-armv8/rfc-v1-port29092022.psci.present
>
> You'll need to fix the numbers of KVM_CAP_ARM_HVC_TO_USER and KVM_CAP_ARM_PSCI_TO_USER
> to match your host kernel. Replace your '-smp' argument with something like:
> | -smp cpus=1,maxcpus=3,cores=3,threads=1,sockets=1
>
> then feed the following to the Qemu montior;
> | (qemu) device_add driver=host-arm-cpu,core-id=1,id=cpu1
> | (qemu) device_del cpu1
>
>
> This series is based on v6.2-rc3, and can be retrieved from:
> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/ virtual_cpu_hotplug/rfc/v1
I applied this patch series on v6.2-rc3 and using the QEMU cloned from
the salil-mehta/qemu.git repo. But when I try to run the QEMU, it shows:
$ qemu-system-aarch64: -accel kvm: Failed to enable
KVM_CAP_ARM_PSCI_TO_USER cap.
Here is the command I use:
$ qemu-system-aarch64
-machine virt
-bios /usr/share/qemu-efi-aarch64/QEMU_EFI.fd
-accel kvm
-m 4096
-smp cpus=1,maxcpus=3,cores=3,threads=1,sockets=1
-cpu host
-qmp unix:./src.socket,server,nowait
-hda ./XXX.qcow2
-serial unix:./src.serial,server,nowait
-monitor stdio
It seems something related to your notice: You'll need to fix the
numbers of KVM_CAP_ARM_HVC_TO_USER and KVM_CAP_ARM_PSCI_TO_USER
to match your host kernel.
But I'm not actually understand what should I fix, since I haven't
review the patch series. Could you give me some more information? Maybe
I'm doing something wrong.
Thanks,
>
>
> Thanks,
>
> James Morse (29):
> ia64: Fix build error due to switch case label appearing next to
> declaration
> ACPI: Move ACPI_HOTPLUG_CPU to be enabled per architecture
> drivers: base: Use present CPUs in GENERIC_CPU_DEVICES
> drivers: base: Allow parts of GENERIC_CPU_DEVICES to be overridden
> drivers: base: Move cpu_dev_init() after node_dev_init()
> arm64: setup: Switch over to GENERIC_CPU_DEVICES using
> arch_register_cpu()
> ia64/topology: Switch over to GENERIC_CPU_DEVICES
> x86/topology: Switch over to GENERIC_CPU_DEVICES
> LoongArch: Switch over to GENERIC_CPU_DEVICES
> arch_topology: Make register_cpu_capacity_sysctl() tolerant to late
> CPUs
> ACPI: processor: Add support for processors described as container
> packages
> ACPI: processor: Register CPUs that are online, but not described in
> the DSDT
> ACPI: processor: Register all CPUs from acpi_processor_get_info()
> ACPI: Rename ACPI_HOTPLUG_CPU to include 'present'
> ACPI: Move acpi_bus_trim_one() before acpi_scan_hot_remove()
> ACPI: Rename acpi_processor_hotadd_init and remove pre-processor
> guards
> ACPI: Add post_eject to struct acpi_scan_handler for cpu hotplug
> ACPI: Check _STA present bit before making CPUs not present
> ACPI: Warn when the present bit changes but the feature is not enabled
> drivers: base: Implement weak arch_unregister_cpu()
> LoongArch: Use the __weak version of arch_unregister_cpu()
> arm64: acpi: Move get_cpu_for_acpi_id() to a header
> ACPICA: Add new MADT GICC flags fields [code first?]
> arm64, irqchip/gic-v3, ACPI: Move MADT GICC enabled check into a
> helper
> irqchip/gic-v3: Don't return errors from gic_acpi_match_gicc()
> irqchip/gic-v3: Add support for ACPI's disabled but 'online capable'
> CPUs
> ACPI: add support to register CPUs based on the _STA enabled bit
> arm64: document virtual CPU hotplug's expectations
> cpumask: Add enabled cpumask for present CPUs that can be brought
> online
>
> Jean-Philippe Brucker (3):
> arm64: psci: Ignore DENIED CPUs
> KVM: arm64: Pass hypercalls to userspace
> KVM: arm64: Pass PSCI calls to userspace
>
> Documentation/arm64/cpu-hotplug.rst | 79 ++++++++++++
> Documentation/arm64/index.rst | 1 +
> Documentation/virt/kvm/api.rst | 31 ++++-
> Documentation/virt/kvm/arm/hypercalls.rst | 1 +
> arch/arm64/Kconfig | 1 +
> arch/arm64/include/asm/acpi.h | 11 ++
> arch/arm64/include/asm/cpu.h | 1 -
> arch/arm64/include/asm/kvm_host.h | 2 +
> arch/arm64/kernel/acpi_numa.c | 11 --
> arch/arm64/kernel/psci.c | 2 +-
> arch/arm64/kernel/setup.c | 13 +-
> arch/arm64/kernel/smp.c | 5 +-
> arch/arm64/kvm/arm.c | 15 ++-
> arch/arm64/kvm/hypercalls.c | 28 ++++-
> arch/arm64/kvm/psci.c | 13 ++
> arch/ia64/Kconfig | 2 +
> arch/ia64/include/asm/acpi.h | 2 +-
> arch/ia64/include/asm/cpu.h | 11 --
> arch/ia64/kernel/acpi.c | 6 +-
> arch/ia64/kernel/setup.c | 2 +-
> arch/ia64/kernel/sys_ia64.c | 7 +-
> arch/ia64/kernel/topology.c | 35 +-----
> arch/loongarch/Kconfig | 2 +
> arch/loongarch/kernel/topology.c | 31 +----
> arch/x86/Kconfig | 2 +
> arch/x86/include/asm/cpu.h | 6 -
> arch/x86/kernel/acpi/boot.c | 4 +-
> arch/x86/kernel/topology.c | 19 +--
> drivers/acpi/Kconfig | 5 +-
> drivers/acpi/acpi_processor.c | 146 +++++++++++++++++-----
> drivers/acpi/processor_core.c | 2 +-
> drivers/acpi/scan.c | 116 +++++++++++------
> drivers/base/arch_topology.c | 38 ++++--
> drivers/base/cpu.c | 31 ++++-
> drivers/base/init.c | 2 +-
> drivers/firmware/psci/psci.c | 2 +
> drivers/irqchip/irq-gic-v3.c | 38 +++---
> include/acpi/acpi_bus.h | 1 +
> include/acpi/actbl2.h | 1 +
> include/kvm/arm_hypercalls.h | 1 +
> include/kvm/arm_psci.h | 4 +
> include/linux/acpi.h | 10 +-
> include/linux/cpu.h | 6 +
> include/linux/cpumask.h | 25 ++++
> include/uapi/linux/kvm.h | 2 +
> kernel/cpu.c | 3 +
> 46 files changed, 532 insertions(+), 244 deletions(-)
> create mode 100644 Documentation/arm64/cpu-hotplug.rst
>
--
Shaoqin
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