Re: [PATCH v4 5/5] RISC-V: KVM: Add the eager_page_split module parameter

[Anup Patel]

On Wed, Jul 1, 2026 at 5:41 PM Wang Yechao <wang.yechao255@xxxxxxxxxx> wrote:
>
> Add an eager_page_split module parameter for RISC-V KVM, following
> the same approach as on x86. This parameter controls whether eager
> page splitting is enabled. The default value is on.
>
> When eager page splitting is enabled, KVM proactively splits large
> pages (huge pages) into smaller pages when needed for dirty logging
> or other operations. Disabling it can be beneficial for VM workloads
> that rarely perform writes, or that only write to a small region of
> memory, as it allows huge pages to remain intact for read accesses.
>
> Signed-off-by: Wang Yechao <wang.yechao255@xxxxxxxxxx>

LGTM.

Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>

Thanks,
Anup

> ---
>  Documentation/admin-guide/kernel-parameters.txt |  7 +++++--
>  arch/riscv/kvm/mmu.c                            | 13 ++++++++++---
>  2 files changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a68003c3599cc..b4c68a896fa79 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3047,7 +3047,7 @@ Kernel parameters
>                         Default is 0 (don't ignore, but inject #GP)
>
>         kvm.eager_page_split=
> -                       [KVM,X86] Controls whether or not KVM will try to
> +                       [KVM,X86,RISCV] Controls whether or not KVM will try to
>                         proactively split all huge pages during dirty logging.
>                         Eager page splitting reduces interruptions to vCPU
>                         execution by eliminating the write-protection faults
> @@ -3067,7 +3067,10 @@ Kernel parameters
>                         the KVM_CLEAR_DIRTY ioctl, and only for the pages being
>                         cleared.
>
> -                       Eager page splitting is only supported when kvm.tdp_mmu=Y.
> +                       On x86, eager page splitting is only supported when
> +                       kvm.tdp_mmu=Y.
> +
> +                       On RISCV, eager page splitting is supported by default.
>
>                         Default is Y (on).
>
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 29a7ac023d4db..a534f596c8ca0 100644
> --- a/arch/riscv/kvm/mmu.c
> +++ b/arch/riscv/kvm/mmu.c
> @@ -16,6 +16,9 @@
>  #include <asm/kvm_mmu.h>
>  #include <asm/kvm_nacl.h>
>
> +static bool __read_mostly eager_page_split = true;
> +module_param(eager_page_split, bool, 0644);
> +
>  static void mmu_wp_memory_region(struct kvm *kvm, int slot)
>  {
>         struct kvm_memslots *slots = kvm_memslots(kvm);
> @@ -167,8 +170,10 @@ void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
>
>         kvm_riscv_gstage_wp_range(&gstage, start, end);
>
> -       if (kvm_dirty_log_manual_protect_and_init_set(kvm))
> -               mmu_split_huge_pages(&gstage, start, end);
> +       if (kvm_dirty_log_manual_protect_and_init_set(kvm)) {
> +               if (READ_ONCE(eager_page_split))
> +                       mmu_split_huge_pages(&gstage, start, end);
> +       }
>  }
>
>  void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot)
> @@ -238,7 +243,9 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>                 if (kvm_dirty_log_manual_protect_and_init_set(kvm))
>                         return;
>                 mmu_wp_memory_region(kvm, new->id);
> -               mmu_split_memory_region(kvm, new->id);
> +
> +               if (READ_ONCE(eager_page_split))
> +                       mmu_split_memory_region(kvm, new->id);
>         }
>  }
>
> --
> 2.43.5
>