[PATCH v2 0/2] RISC-V: KVM: Add PMU event filter support

["Yuhang.chen" <yhchen312@gmail.com>]

This series adds PMU event filter support to RISC-V KVM, allowing a
userspace VMM to restrict which SBI PMU events a guest is permitted to
program.

The KVM_SET_PMU_EVENT_FILTER ioctl and KVM_CAP_PMU_EVENT_FILTER already
exist as generic KVM uAPI (include/uapi/linux/kvm.h); RISC-V KVM does
not yet implement them.  Wiring them up lets a VMM limit a guest's PMU
event access, which is useful for sandboxing and for withholding host
PMU events the host does not intend to expose.

Patch 1 implements the kernel side: the uapi struct, the ioctl handler
with an SRCU-protected filter, enforcement in
kvm_riscv_vcpu_pmu_ctr_cfg_match() (a disallowed event fails with
SBI_ERR_NOT_SUPPORTED), and advertisement of KVM_CAP_PMU_EVENT_FILTER.
Like the other arch-specific KVM uAPI structs, struct
kvm_pmu_event_filter is defined per-architecture; its layout reflects
RISC-V PMU events and the ioctl number encodes the struct size.

Patch 2 adds a selftest that covers the ALLOW/DENY semantics with the
event in and out of the list, filter clearing, and ioctl argument
rejection (EINVAL/E2BIG).

Testing: built and run under QEMU TCG with nested KVM (an L1 KVM host
running an L2 guest).  The selftest (patch 2) passes and dmesg stays
clean throughout the run.

Based on v7.2-rc2 (a635d6748234).

Changes in v2:
- Mask reserved high bits of the SBI PMU event index before comparing
  against the filter, so a guest cannot bypass a DENY filter by setting
  bits above bit 19.  Noted by sashiko-bot review.
- Reject non-zero pad in the ioctl argument to keep the field usable
  for future extensions.

Assisted-by: YuanSheng:deepseek-v4-pro
Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
Signed-off-by: Yuhang.chen <yhchen312@gmail.com>

Yuhang.chen (2):
  RISC-V: KVM: Add PMU event filter support
  RISC-V: KVM: selftests: Add PMU event filter test

 arch/riscv/include/asm/kvm_host.h             |   3 +
 arch/riscv/include/uapi/asm/kvm.h             |  20 ++
 arch/riscv/kvm/vcpu_pmu.c                     |  31 +++
 arch/riscv/kvm/vm.c                           |  69 +++++-
 tools/testing/selftests/kvm/Makefile.kvm      |   1 +
 .../kvm/riscv/pmu_event_filter_test.c         | 199 ++++++++++++++++++
 6 files changed, 322 insertions(+), 1 deletion(-)
 create mode 100644 tools/testing/selftests/kvm/riscv/pmu_event_filter_test.c

--
2.34.1