Hi Russell, > On 24 Oct 2023, at 15:15, Russell King (Oracle) <linux@xxxxxxxxxxxxxxx> wrote: > > Hi, > > I'm posting James' patch set updated with most of the review comments > from his RFC v2 series back in September. Individual patches have a > changelog attached at the bottom of the commit message. Those which > I have finished updating have my S-o-b on them, those which still have > outstanding review comments from RFC v2 do not. In some of these cases > I've asked questions and am waiting for responses. > > I'm posting this as RFC v3 because there's still some unaddressed > comments and it's clearly not ready for merging. Even if it was ready > to be merged, it is too late in this development cycle to be taking > this change in, so there would be little point posting it non-RFC. > Also James stated that he's waiting for confirmation from the > Kubernetes/Kata folk - I have no idea what the status is there. > > I will be sending each patch individually to a wider audience > appropriate for that patch - apologies to those missing out on this > cover message. I have added more mailing lists to the series with the > exception of the acpica list in a hope of this cover message also > reaching those folk. > > The changes that aren't included are: > > 1. Updates for my patch that was merged via Thomas (thanks!): > c4dd854f740c cpu-hotplug: Provide prototypes for arch CPU registration > rather than having this change spread through James' patches. > > 2. New patch - simplification of PA-RISC's smp_prepare_boot_cpu() > > 3. Moved "ACPI: Use the acpi_device_is_present() helper in more places" > and "ACPI: Rename acpi_scan_device_not_present() to be about > enumeration" to the beginning of the series - these two patches are > already queued up for merging into 6.7. > > 4. Moved "arm64, irqchip/gic-v3, ACPI: Move MADT GICC enabled check into > a helper" to the beginning of the series, which has been submitted, > but as yet the fate of that posting isn't known. > > The first four patches in this series are provided for completness only. > > There is an additional patch in James' git tree that isn't in the set > of patches that James posted: "ACPI: processor: Only call > arch_unregister_cpu() if HOTPLUG_CPU is selected" which looks to me to > be a workaround for arch_unregister_cpu() being under the ifdef. I've > commented on this on the RFC v2 posting making a suggestion, but as yet > haven't had any response. > > I've included almost all of James' original covering body below the > diffstat. > > The reason that I'm doing this is to help move this code forward so > hopefully it can be merged - which is why I have been keen to dig out > from James' patches anything that can be merged and submit it > separately, since this is a feature for which some users have a > definite need for. > > Please note that I haven't tested this beyond building for aarch64 at > the present time. > > The series can be found at: > > git://git.armlinux.org.uk/~rmk/linux-arm.git aarch64/hotplug-vcpu/v6.6-rc7 > > Documentation/arch/arm64/cpu-hotplug.rst | 79 +++++++++++++++ > Documentation/arch/arm64/index.rst | 1 + > arch/arm64/Kconfig | 1 + > arch/arm64/include/asm/acpi.h | 11 +++ > arch/arm64/include/asm/cpu.h | 1 - > 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/ia64/Kconfig | 3 + > arch/ia64/include/asm/acpi.h | 2 +- > arch/ia64/include/asm/cpu.h | 6 -- > arch/ia64/kernel/acpi.c | 6 +- > arch/ia64/kernel/setup.c | 2 +- > arch/ia64/kernel/topology.c | 35 +------ > arch/loongarch/Kconfig | 2 + > arch/loongarch/configs/loongson3_defconfig | 2 +- > arch/loongarch/kernel/acpi.c | 4 +- > arch/loongarch/kernel/topology.c | 38 +------- > arch/parisc/kernel/smp.c | 8 +- > arch/riscv/Kconfig | 1 + > arch/riscv/kernel/setup.c | 19 +--- > arch/x86/Kconfig | 3 + > arch/x86/include/asm/cpu.h | 4 - > arch/x86/kernel/acpi/boot.c | 4 +- > arch/x86/kernel/cpu/intel_epb.c | 2 +- > arch/x86/kernel/topology.c | 27 +----- > drivers/acpi/Kconfig | 14 ++- > drivers/acpi/acpi_processor.c | 151 +++++++++++++++++++++++------ > drivers/acpi/bus.c | 16 +++ > drivers/acpi/device_pm.c | 2 +- > drivers/acpi/device_sysfs.c | 2 +- > drivers/acpi/internal.h | 1 - > drivers/acpi/processor_core.c | 2 +- > drivers/acpi/property.c | 2 +- > drivers/acpi/scan.c | 148 ++++++++++++++++++---------- > drivers/base/arch_topology.c | 38 +++++--- > drivers/base/cpu.c | 44 +++++++-- > drivers/base/init.c | 2 +- > drivers/base/node.c | 7 -- > 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/linux/acpi.h | 13 ++- > include/linux/cpu.h | 4 + > include/linux/cpumask.h | 25 +++++ > kernel/cpu.c | 3 + > 48 files changed, 516 insertions(+), 292 deletions(-) > > > On Wed, Sep 13, 2023 at 04:37:48PM +0000, James Morse wrote: >> Hello! >> >> Changes since RFC-v1: >> * riscv is new, ia64 is gone >> * The KVM support is different, and upstream - no need to patch the host. >> >> --- >> >> 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. >> >> I've only build tested Loongarch and riscv. I've removed the ia64 specific >> patches, but left the changes in other patches to make git-grep review of >> renames easier. >> >> 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-v2-rc6 >> >> 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 >> >> >> Why is this still an RFC? I'm still looking for confirmation from the >> kubernetes/kata folk that this works for them. Because of this I've culled >> the CC list... >> >> >> This series is based on v6.6-rc1, and can be retrieved from: >> https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/ virtual_cpu_hotplug/rfc/v2 >> >> >> Thanks, >> >> James Morse (34): >> ACPI: Move ACPI_HOTPLUG_CPU to be disabled on arm64 and riscv >> 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() >> drivers: base: Print a warning instead of panic() when register_cpu() >> fails >> arm64: setup: Switch over to GENERIC_CPU_DEVICES using >> arch_register_cpu() >> x86: intel_epb: Don't rely on link order >> x86/topology: Switch over to GENERIC_CPU_DEVICES >> LoongArch: Switch over to GENERIC_CPU_DEVICES >> riscv: Switch over to GENERIC_CPU_DEVICES >> arch_topology: Make register_cpu_capacity_sysctl() tolerant to late >> CPUs >> ACPI: Use the acpi_device_is_present() helper in more places >> ACPI: Rename acpi_scan_device_not_present() to be about enumeration >> ACPI: Only enumerate enabled (or functional) devices >> 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 >> ACPI: Add _OSC bits to advertise OS support for toggling CPU >> present/enabled >> cpumask: Add enabled cpumask for present CPUs that can be brought >> online >> >> Jean-Philippe Brucker (1): >> arm64: psci: Ignore DENIED CPUs > Tested on QEMU, based on Salil's RFC v2 [1], running with KVM. - boot - hotplug up to 'maxcpus' - hotunplug down to the number of boot cpus - hotplug vcpus and migrate with vcpus offline - hotplug vcpus and migrate with vcpus online - hotplug vcpus then unplug vcpus then migrate - successive live migrations (up until 6) Feel free to add: Tested-by: Miguel Luis <miguel.luis@xxxxxxxxxx> Thank you Miguel [1] https://lore.kernel.org/qemu-devel/20230926100436.28284-1-salil.mehta@xxxxxxxxxx/ > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 80Mbps down 10Mbps up. Decent connectivity at last! >
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