[PATCH v6 0/4] Support runtime configuration for per-VM's HGATP mode

[fangyu.yu@linux.alibaba.com]

From: Fangyu Yu <fangyu.yu@linux.alibaba.com>

Currently, RISC-V KVM hardcodes the G-stage page table format (HGATP mode)
to the maximum mode detected at boot time (e.g., SV57x4 if supported). but
often such a wide GPA is unnecessary, just as a host sometimes doesn't need
sv57.

This patch introduces per-VM configurability of the G-stage mode via a new
KVM capability: KVM_CAP_RISCV_SET_HGATP_MODE. User-space can now explicitly
request a specific HGATP mode (SV39x4, SV48x4, SV57x4 or SV32x4) during
VM creation.

---
Changes in v6 (Anup's suggestions):
    - Reworked kvm_riscv_gstage_gpa_bits() and kvm_riscv_gstage_gpa_size() to
      take "unsigned long pgd_levels" instead of "struct kvm_arch *".
    - Moved kvm_riscv_gstage_mode() helper from kvm_host.h to kvm_gstage.h.
    - Renamed kvm->arch.kvm_riscv_gstage_pgd_levels to kvm->arch.pgd_levels.
    - Added pgd_levels to struct kvm_gstage to avoid repeated
      gstage->kvm->arch pointer chasing.
    - Link to v5:
      https://lore.kernel.org/linux-riscv/20260204134507.33912-1-fangyu.yu@linux.alibaba.com/
---
Changes in v5:
    - Use architectural HGATP.MODE encodings as the bit index for the supported-mode
      bitmap and for the VM-mode selection UAPI; no new UAPI mode/bit defines are
      introduced(per Radim).
    - Allow KVM_CAP_RISCV_SET_HGATP_MODE on RV32 as well(per Drew).
    - Link to v4:
      https://lore.kernel.org/linux-riscv/20260202140716.34323-1-fangyu.yu@linux.alibaba.com/
---
Changes in v4:
    - Extend kvm_riscv_gstage_mode_detect() to probe all HGATP.MODE values
      supported by the host and record them in a bitmask.
    - Treat unexpected pgd_levels in kvm_riscv_gstage_mode() as an internal error
      (e.g. WARN_ON_ONCE())(per Radim).
    - Move kvm_riscv_gstage_gpa_bits() and kvm_riscv_gstage_gpa_size() to header
      as static inline helpers(per Radim).
    - Drop gstage_mode_user_initialized and Remove the kvm_debug() message from
      KVM_CAP_RISCV_SET_HGATP_MODE(per Radim).
    - Link to v3:
      https://lore.kernel.org/linux-riscv/20260125150450.27068-1-fangyu.yu@linux.alibaba.com/
---
Changes in v3:
    - Reworked the patch formatting (per Drew).
    - Dropped kvm->arch.kvm_riscv_gstage_mode and derive HGATP.MODE from
      kvm_riscv_gstage_pgd_levels via a helper, avoiding redundant per-VM state(per Drew).
    - Removed kvm_riscv_gstage_max_mode and keep only kvm_riscv_gstage_max_pgd_levels
      for host capability detection(per Drew).
    - Other initialization and return value issues(per Drew).
    - Enforce that KVM_CAP_RISCV_SET_HGATP_MODE can only be enabled before any vCPUs
      are created by rejecting the ioctl once kvm->created_vcpus is non-zero(per Radim).
    - Add a memslot safety check and reject the capability unless
      kvm_are_all_memslots_empty(kvm) is true, ensuring the G-stage format is not
      changed after any memslots have been installed(per Radim).
    - Link to v2:
      https://lore.kernel.org/linux-riscv/20260105143232.76715-1-fangyu.yu@linux.alibaba.com/

Fangyu Yu (4):
  RISC-V: KVM: Support runtime configuration for per-VM's HGATP mode
  RISC-V: KVM: Cache gstage pgd_levels in struct kvm_gstage
  RISC-V: KVM: Detect and expose supported HGATP G-stage modes
  RISC-V: KVM: add KVM_CAP_RISCV_SET_HGATP_MODE

 Documentation/virt/kvm/api.rst      |  27 ++++++++
 arch/riscv/include/asm/kvm_gstage.h |  58 ++++++++++++++--
 arch/riscv/include/asm/kvm_host.h   |   1 +
 arch/riscv/kvm/gstage.c             | 102 ++++++++++++++--------------
 arch/riscv/kvm/main.c               |  12 ++--
 arch/riscv/kvm/mmu.c                |  70 ++++++-------------
 arch/riscv/kvm/vm.c                 |  20 +++++-
 arch/riscv/kvm/vmid.c               |   3 +-
 include/uapi/linux/kvm.h            |   1 +
 9 files changed, 178 insertions(+), 116 deletions(-)

-- 
2.50.1