Re: [PATCH v8 0/3] Support runtime configuration for per-VM's HGATP mode

[Anup Patel]

On Fri, Apr 3, 2026 at 9:00 PM <fangyu.yu@xxxxxxxxxxxxxxxxx> wrote:
>
> From: Fangyu Yu <fangyu.yu@xxxxxxxxxxxxxxxxx>
>
> 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 reuse KVM_CAP_VM_GPA_BITS to select HGATP.MODE. User-space can
> now explicitly request a specific HGATP mode (SV39x4, SV48x4, SV57x4 or
> SV32x4) during VM creation.
>
> ---
> Changes in v8:
>     - Reuse KVM_CAP_VM_GPA_BITS to advertise and select the effective GPA width
>       for a VM (Anup's suggestion).
>     - Handle the kvm == NULL case and task kvm->lock and kvm->slots_lock to serialize
>       against concurrent vCPU creation and memslot updates (Radim's suggestion).
>     - Link to v7:
>       https://lore.kernel.org/linux-riscv/20260402132303.6252-1-fangyu.yu@xxxxxxxxxxxxxxxxx/
> ---
> Changes in v7 (Anup's suggestions):
>     - Keep the original HGATP mode probing logic.
>     - Link to v6:
>       https://lore.kernel.org/linux-riscv/20260330122601.22140-1-fangyu.yu@xxxxxxxxxxxxxxxxx/
> ---
> 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@xxxxxxxxxxxxxxxxx/
> ---
> 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@xxxxxxxxxxxxxxxxx/
> ---
> 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@xxxxxxxxxxxxxxxxx/
> ---
> 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@xxxxxxxxxxxxxxxxx/
>
> Fangyu Yu (3):
>   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: Reuse KVM_CAP_VM_GPA_BITS to select HGATP.MODE
>
>  arch/riscv/include/asm/kvm_gstage.h | 47 ++++++++++++++++---
>  arch/riscv/include/asm/kvm_host.h   |  1 +
>  arch/riscv/kvm/gstage.c             | 65 +++++++++++++--------------
>  arch/riscv/kvm/main.c               | 12 ++---
>  arch/riscv/kvm/mmu.c                | 70 +++++++++--------------------
>  arch/riscv/kvm/vm.c                 | 49 ++++++++++++++++++--
>  arch/riscv/kvm/vmid.c               |  3 +-
>  7 files changed, 148 insertions(+), 99 deletions(-)
>
> --
> 2.50.1
>

This series is in good shape now. I will wait one more day to see
if there are any comments and after that I will merge for Linux-7.1

Thanks,
Anup