[PATCH v3 0/8] KVM: arm64: vCPU preempted check support

[Zengruan Ye]

This patch set aims to support the vcpu_is_preempted() functionality
under KVM/arm64, which allowing the guest to obtain the vCPU is
currently running or not. This will enhance lock performance on
overcommitted hosts (more runnable vCPUs than physical CPUs in the
system) as doing busy waits for preempted vCPUs will hurt system
performance far worse than early yielding.

We have observed some performace improvements in uninx benchmark tests.

unix benchmark result:
  host:  kernel 5.5.0-rc5, HiSilicon Kunpeng920, 8 CPUs
  guest: kernel 5.5.0-rc5, 16 vCPUs

               test-case                |    after-patch    |   before-patch
----------------------------------------+-------------------+------------------
 Dhrystone 2 using register variables   | 334600751.0 lps   | 335319028.3 lps
 Double-Precision Whetstone             |     32856.1 MWIPS |     32849.6 MWIPS
 Execl Throughput                       |      3662.1 lps   |      2718.0 lps
 File Copy 1024 bufsize 2000 maxblocks  |    432906.4 KBps  |    158011.8 KBps
 File Copy 256 bufsize 500 maxblocks    |    116023.0 KBps  |     37664.0 KBps
 File Copy 4096 bufsize 8000 maxblocks  |   1432769.8 KBps  |    441108.8 KBps
 Pipe Throughput                        |   6405029.6 lps   |   6021457.6 lps
 Pipe-based Context Switching           |    185872.7 lps   |    184255.3 lps
 Process Creation                       |      4025.7 lps   |      3706.6 lps
 Shell Scripts (1 concurrent)           |      6745.6 lpm   |      6436.1 lpm
 Shell Scripts (8 concurrent)           |       998.7 lpm   |       931.1 lpm
 System Call Overhead                   |   3913363.1 lps   |   3883287.8 lps
----------------------------------------+-------------------+------------------
 System Benchmarks Index Score          |      1835.1       |      1327.6

Changes from v2:
https://lore.kernel.org/lkml/20191226135833.1052-1-yezengruan@xxxxxxxxxx/
 * Post Will's patches as part of this series [1][2], and add the
   probing logic for checking whether the hypervisor is KVM or not
 * Clear PV-lock interface documentation
 * Remove preempted state field
 * Fix build error when CONFIG_PARAVIRT is not set
 * Bunch of typo fixes.

Changes from v1:
https://lore.kernel.org/lkml/20191217135549.3240-1-yezengruan@xxxxxxxxxx/
 * Guest kernel no longer allocates the PV lock structure, instead it
   is allocated by user space to avoid lifetime issues about kexec.
 * Provide vCPU attributes for PV lock.
 * Update SMC number of PV lock features.
 * Report some basic validation when PV lock init.
 * Document preempted field.
 * Bunch of typo fixes.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=kvm/hvc&id=464f5a1741e5959c3e4d2be1966ae0093b4dce06

[2] https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/commit/?h=kvm/hvc&id=6597490e005d0eeca8ed8c1c1d7b4318ee014681

Will Deacon (2):
  arm64: Probe for the presence of KVM hypervisor services during boot
  arm/arm64: KVM: Advertise KVM UID to guests via SMCCC

Zengruan Ye (6):
  KVM: arm64: Document PV-lock interface
  KVM: arm64: Add SMCCC paravirtualised lock calls
  KVM: arm64: Support pvlock preempted via shared structure
  KVM: arm64: Provide vCPU attributes for PV lock
  KVM: arm64: Add interface to support vCPU preempted check
  KVM: arm64: Support the vCPU preemption check

 Documentation/virt/kvm/arm/pvlock.rst   |  68 +++++++++++++
 Documentation/virt/kvm/devices/vcpu.txt |  14 +++
 arch/arm/include/asm/kvm_host.h         |  18 ++++
 arch/arm64/include/asm/hypervisor.h     |  11 ++
 arch/arm64/include/asm/kvm_host.h       |  27 +++++
 arch/arm64/include/asm/paravirt.h       |  15 +++
 arch/arm64/include/asm/pvlock-abi.h     |  16 +++
 arch/arm64/include/asm/spinlock.h       |   9 ++
 arch/arm64/include/uapi/asm/kvm.h       |   2 +
 arch/arm64/kernel/Makefile              |   2 +-
 arch/arm64/kernel/paravirt-spinlocks.c  |  13 +++
 arch/arm64/kernel/paravirt.c            | 129 +++++++++++++++++++++++-
 arch/arm64/kernel/setup.c               |  37 +++++++
 arch/arm64/kvm/Makefile                 |   1 +
 arch/arm64/kvm/guest.c                  |   9 ++
 include/linux/arm-smccc.h               |  36 +++++++
 include/linux/cpuhotplug.h              |   1 +
 include/uapi/linux/kvm.h                |   2 +
 virt/kvm/arm/arm.c                      |   8 ++
 virt/kvm/arm/hypercalls.c               |  54 +++++++---
 virt/kvm/arm/pvlock.c                   | 102 +++++++++++++++++++
 21 files changed, 559 insertions(+), 15 deletions(-)
 create mode 100644 Documentation/virt/kvm/arm/pvlock.rst
 create mode 100644 arch/arm64/include/asm/pvlock-abi.h
 create mode 100644 arch/arm64/kernel/paravirt-spinlocks.c
 create mode 100644 virt/kvm/arm/pvlock.c

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2.19.1