[PATCH RFC v4 0/4] RISC-V: Add PARAVIRT_SPINLOCKS support

[GUO Ren (XuanTie)]

Paravirtualized spinlocks allow an unfair qspinlock to replace the
ticket-lock or native fair qspinlock implementation with something
virtualization-friendly, for example, halting the virtual CPU rather
than spinning.

You can observe the paravirt qspinlock behavior with the pv_kick and
pv_wait tracepoints under /sys/kernel/debug/tracing/:

  # echo 1 > /sys/kernel/debug/tracing/events/paravirt/enable
  # cat /sys/kernel/debug/tracing/trace
            TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
               | |         |   |||||     |         |
             sh-100     [001] d..2.    28.312294: pv_wait: cpu 1 out of wfi
         <idle>-0       [000] d.h4.    28.322030: pv_kick: cpu 0 kick target cpu 1

This series is split from [1]. The newest discussion is at [2].

[1]: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@xxxxxxxxxx/
[2]: https://lists.riscv.org/g/tech-prs/message/1211

Changelog:
v4:
 - Rebase onto v7.3-rc4.
 - Normalize the author identity to "GUO Ren (XuanTie)".
 - Minor commit log cleanups (fix line-wrap artifacts and typos).

v3:
https://lore.kernel.org/linux-riscv/20251201003041.695081-1-guoren@xxxxxxxxxx/
 - Rebase on linux-6.18-rc7.
 - Simplify nopvspin usage.

v2:
https://lore.kernel.org/linux-riscv/20241227011011.2331381-1-guoren@xxxxxxxxxx/
 - Add RFC tag.
 - Using new SBI_EXT_PVLOCK ID.
 - Add virt_spin_lock support.
 - Add nopvspin support.

v1:
https://lore.kernel.org/linux-riscv/20241222033917.1754495-1-guoren@xxxxxxxxxx/

GUO Ren (XuanTie) (5):
  RISC-V: Add PARAVIRT_SPINLOCKS support
  RISC-V: paravirt: Add pvqspinlock KVM backend
  RISC-V: paravirt: Add pvqspinlock frontend
  RISC-V: paravirt: pvqspinlock: Add trace point for pv_kick/wait
  RISC-V: paravirt: Support nopvspin to disable PARAVIRT_SPINLOCKS

 .../admin-guide/kernel-parameters.txt         |  2 +-
 arch/riscv/Kconfig                            | 12 +++
 arch/riscv/include/asm/Kbuild                 |  1 -
 arch/riscv/include/asm/kvm_vcpu_sbi.h         |  1 +
 arch/riscv/include/asm/qspinlock.h            | 57 +++++++++++++
 arch/riscv/include/asm/qspinlock_paravirt.h   | 26 ++++++
 arch/riscv/include/asm/sbi.h                  |  5 ++
 arch/riscv/include/uapi/asm/kvm.h             |  1 +
 arch/riscv/kernel/Makefile                    |  2 +
 arch/riscv/kernel/qspinlock_paravirt.c        | 82 +++++++++++++++++++
 arch/riscv/kernel/setup.c                     |  5 ++
 .../kernel/trace_events_filter_paravirt.h     | 58 +++++++++++++
 arch/riscv/kvm/Makefile                       |  1 +
 arch/riscv/kvm/vcpu_sbi.c                     |  4 +
 arch/riscv/kvm/vcpu_sbi_pvlock.c              | 54 ++++++++++++
 15 files changed, 309 insertions(+), 2 deletions(-)
 create mode 100644 arch/riscv/include/asm/qspinlock.h
 create mode 100644 arch/riscv/include/asm/qspinlock_paravirt.h
 create mode 100644 arch/riscv/kernel/qspinlock_paravirt.c
 create mode 100644 arch/riscv/kernel/trace_events_filter_paravirt.h
 create mode 100644 arch/riscv/kvm/vcpu_sbi_pvlock.c

--
2.43.1

---
GUO Ren (XuanTie) (4):
      RISC-V: paravirt: Add pvqspinlock KVM backend
      RISC-V: paravirt: Add pvqspinlock frontend
      RISC-V: paravirt: pvqspinlock: Add trace point for pv_kick/wait
      RISC-V: paravirt: Support nopvspin to disable PARAVIRT_SPINLOCKS

 Documentation/admin-guide/kernel-parameters.txt  |  2 +-
 arch/riscv/Kconfig                               | 12 ++++
 arch/riscv/include/asm/Kbuild                    |  1 -
 arch/riscv/include/asm/kvm_vcpu_sbi.h            |  1 +
 arch/riscv/include/asm/qspinlock.h               | 57 ++++++++++++++++
 arch/riscv/include/asm/qspinlock_paravirt.h      | 26 ++++++++
 arch/riscv/include/asm/sbi.h                     |  5 ++
 arch/riscv/include/uapi/asm/kvm.h                |  1 +
 arch/riscv/kernel/Makefile                       |  2 +
 arch/riscv/kernel/qspinlock_paravirt.c           | 82 ++++++++++++++++++++++++
 arch/riscv/kernel/setup.c                        |  5 ++
 arch/riscv/kernel/trace_events_filter_paravirt.h | 58 +++++++++++++++++
 arch/riscv/kvm/Makefile                          |  1 +
 arch/riscv/kvm/vcpu_sbi.c                        |  4 ++
 arch/riscv/kvm/vcpu_sbi_pvlock.c                 | 54 ++++++++++++++++
 15 files changed, 309 insertions(+), 2 deletions(-)
---
base-commit: 93f51579e7df248780214094418f205253383cc5
change-id: 20260921-pvqspinlock-73ad0cfb45b1

Best regards,
--  
GUO Ren (XuanTie) <guoren@xxxxxxxxxx>