Re: [PATCH 4/4] RISC-V: KVM: Add the eager_page_split module parameter

On Wed, May 13, 2026 at 1:15 PM <[email protected]> wrote:
>
> From: Wang Yechao <[email protected]>
>
> 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 <[email protected]>

Update Documentation/admin-guide/kernel-parameters.txt as part
of this patch.

Regards,
Anup


> ---
>  arch/riscv/kvm/mmu.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c
> index 2cdea3e3ed4b..2af03c48aff3 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>
>
> +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);
> @@ -148,8 +151,10 @@ 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))
> -               kvm_riscv_split_huge_pages(&gstage, start, end, true);
> +       if (kvm_dirty_log_manual_protect_and_init_set(kvm)) {
> +               if (READ_ONCE(eager_page_split))
> +                       kvm_riscv_split_huge_pages(&gstage, start, end, true);
> +       }
>  }
>
>  void kvm_arch_sync_dirty_log(struct kvm *kvm, struct kvm_memory_slot *memslot)
> @@ -214,7 +219,9 @@ 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);
> -               kvm_riscv_split_memory_region(kvm, new->id);
> +
> +               if (READ_ONCE(eager_page_split))
> +                       kvm_riscv_split_memory_region(kvm, new->id);
>         }
>  }
>
> --
> 2.27.0

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