[PATCH v16 0/2] RISC-V IOMMU HPM support

[Zong Li]

This series implements support for the RISC-V IOMMU hardware performance
monitor.

The RISC-V IOMMU PMU driver is implemented as an auxiliary device driver
created by the parent RISC-V IOMMU driver. Therefore, the child driver
can obtain resources and information from the parent device, such as
the MMIO base address and IRQ number.

It seems sashiko-bot is giving conflicting advice about whether to add
a lock to ->read(). No matter if we add it or not, the sashiko-bot always
suggests the opposite. Looking at no lock case again, sashiko-bot
concerns about a BPF program calling bpf_perf_event_read() from NMI
context and self-deadlocking against the IRQ handler, but that scenario
cannot occur here:

  - bpf_perf_event_read() goes through perf_event_read_local(), which
    refuses to call ->read() unless event_cpu == smp_processor_id()
    (kernel/events/core.c). All events on this PMU are CPU-bound and
    non-task-bound (->event_init() forces event->cpu = pmu->on_cpu and
    rejects sampling events), so PERF_ATTACH_TASK is never set.
  - More fundamentally, perf overflow interrupts are not NMIs on RISC-V,
    and every pmu->lock critical section in this driver is held under
    raw_spin_lock_irqsave(). There is no context that can interrupt them
    and re-enter ->read().

No other driver under drivers/perf/ uses a trylock or in_nmi() check in
its ->read() callback, so dropping it also brings this driver in line
with the rest.

sashiko-bot also reported that migration calling trigger a NULL pointer
dereference. I don't think this can happen on current mainline.
perf_pmu_migrate_context() does not touch pmu->cpu_pmu_context unless it
actually finds events to migrate. This used to be a real hazard: before
commit bd2756811766 ("perf: Rewrite core context handling", v6.2-rc1)
the first two lines were per_cpu_ptr(pmu->pmu_cpu_context, ...), which
did dereference a pmu-owned pointer unconditionally. That is also why
several in-tree drivers pre-seed thier ->cpu field with a real CPU number
rather than a sentinel, and so do call perf_pmu_migrate_context() in
this window, without any reported oops.

Changed in v15:
- Rebasd onto v7.3-rc6
- Use devm_add_action() instead of devm_add_action_or_reset() for pmu
  unregister. Reported by sashiko-bot
- Move local64_set() before riscv_iommu_pmu_set_counter() in
  set_period(). Reported by sashiko-bot

Changed in v14:
- Rebased onto v7.3-rc5
- Support sparse counters and the different width of each counter
- Accecpt custom event ranges
- Verify IDT supported in event
- Add warning message if riscv_iommu_hpm_enable is failure
- Remove raw_spin_lock for ->read() flow

Changed in v13:
- Reorder the registration of cpuhp action

Changed in v12:
- Rebased onto v7.3-rc4
- Add raw_spin_trylock_irqsave for ->read() flow

Changed in v11:
- Rebased onto v7.3-rc3
- Add riscv_iommu_hpm_disaable to destroy aux dev before MSI is freed
- Fix CPU hotplug race risks reported by sashiko-bot as follows
- Re-validate pre_count after reading hw counter
- Move hwc-state into atomic critical section (pmu->lock)

Changed in v10:
- Optimize hi-lo-hi by do while for hypervisor case
- Add raw spinlock for cpu hotplug race and IRQCHIP_MOVE_DEFERRED
- Remove irq work mechanism for IRQCHIP_MOVE_DEFERRED

Changed in v9:
- Clear PMIP in irq handler on wrong CPU for re-triggering IRQ
- Add a lock in offline_cpu to avoid cpu hotplug race condition

Changed in v8:
- Rebased onto v7.3-rc2
- Add irq work mechanism for IRQCHIP_MOVE_DEFERRED case
- Filter multiple cycle event case

Changed in v7:
- Rebased onto the v7.3-rc1
- Remove raw spinlock
- Check CPU matching at the beginning of irq handler
- Add PERF_HES_STOPPED check before overflow handling

Changed in v6:
- Rebased onto the latest v7.3-rc
- Use sysfs_emit instead of cpumap_print_to_pagebuf
- Set up on_cpu and irq affinity by cpuhp callbacks
- Change type of on_cpu from unsigned int to int
- Reject filter operands of cycle event in event_init
- Check return value of counter number and  masks in probe
- Add raw spinlock for race condition (third commit)

Changed in v5:
- Pick up suggestions from sashiko-bot as follows
- Fix event group validation for sw event
- Bind IRQ to aux PMU dev instead of parent IOMMU dev
- Clear OF bit when event is NULL
- Improve hi-lo-hi patten
- Add back IRQF_SHARED flag due to mismatch
- Manage cpuhp and pmu register by devre

Changed in v4:
- Rebased onto v7.3-rc
- Use is_sampling_event() instead of accessing vairable directly
- Rename the matching name from "iommu.pmu" to "riscv-iommu.pmu"
- Change the naming of PMU device for avoid ":" in PCIe case
- Add suppress_bind_attrs attribute
- Remove IRQF_SHARED flag
- Set irq affinity to local CPU of IOMMU
- Allocate ID by IDA for auxiliary device
- Pick up suggestions from sashiko-bot

Changed in v3:
- Rebased onto v7.2-rc3
- Use hi_lo_writeq/readq to access register
- Pick comments from sashiko-bot as follows
- Set IRQ CPU affinity
- Remove IRQF_ONESHOT flag when request irq
- Adjust cycle event check by checking event_id field only
- Fix bug for group events verificaiton
- Fix KASAN issue about casting 32-bit variable to unsigned long pointer
- Clear IPSR pending bit before starting counter
- Clear OF bit in event selector register in irq handler
- Release irq by devm instead of explicit free_irq

Changed in v2:
- Rebased onto v7.2-rc1
- Use hi-lo-hi mechanism to read counter.
  Suggested by Guo Ren and David Laight

Changed in v1:
- Rebased onto v6.19-rc8
- Pick all suggestions and feedbacks from v1 series
- Add cpu hotplug implementation to avoid race enablement
- Move PMU-related definition from header to c file
- Change PMU driver to auxiliary device driver

Changed in RFC:
- Rebase onto v6.13-rc7
- Clear interrupt pending before handling interrupt
- Fix the counter value issue caused by OF bit in the cycle counter.
- Invoke riscv_iommu_hpm_disable() instead of riscv_iommu_pmu_uninit()
  in riscv_iommu_remove()

Zong Li (2):
  drivers/perf: riscv-iommu: add risc-v iommu pmu driver
  iommu/riscv: create a auxiliary device for HPM

 drivers/iommu/riscv/Kconfig      |    1 +
 drivers/iommu/riscv/iommu-bits.h |   61 --
 drivers/iommu/riscv/iommu.c      |   58 ++
 drivers/iommu/riscv/iommu.h      |    4 +
 drivers/perf/Kconfig             |   12 +
 drivers/perf/Makefile            |    1 +
 drivers/perf/riscv_iommu_pmu.c   | 1102 ++++++++++++++++++++++++++++++
 7 files changed, 1178 insertions(+), 61 deletions(-)
 create mode 100644 drivers/perf/riscv_iommu_pmu.c

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2.43.7