Re: [PATCH v3 1/3] RISC-V: KVM: Fix lost write protection on huge pages during dirty logging

[Anup Patel]

On Mon, Mar 16, 2026 at 11:46 AM <wang.yechao255@xxxxxxxxxx> wrote:
>
> From: Wang Yechao <wang.yechao255@xxxxxxxxxx>
>
> When enabling dirty log in small chunks (e.g., QEMU default chunk
> size of 256K), the chunk size is always smaller than the page size
> of huge pages (1G or 2M) used in the gstage page tables. This caused
> the write protection to be incorrectly skipped for huge PTEs because
> the condition `(end - addr) >= page_size` was not satisfied.
>
> Remove the size check in `kvm_riscv_gstage_wp_range()` to ensure huge
> PTEs are always write-protected regardless of the chunk size. Additionally,
> explicitly align the address down to the page size before invoking
> `kvm_riscv_gstage_op_pte()` to guarantee that the address passed to the
> operation function is page-aligned.
>
> This fixes the issue where dirty pages might not be tracked correctly
> when using huge pages.
>
> Fixes: 9d05c1fee837 ("RISC-V: KVM: Implement stage2 page table programming")
> Signed-off-by: Wang Yechao <wang.yechao255@xxxxxxxxxx>
> Reviewed-by: Nutty Liu <nutty.liu@xxxxxxxxxxx>

LGTM.

Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>

Regards,
Anup


> ---
>  arch/riscv/kvm/gstage.c | 7 +++----
>  1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
> index b67d60d722c2..d2001d508046 100644
> --- a/arch/riscv/kvm/gstage.c
> +++ b/arch/riscv/kvm/gstage.c
> @@ -304,10 +304,9 @@ void kvm_riscv_gstage_wp_range(struct kvm_gstage *gstage, gpa_t start, gpa_t end
>                 if (!found_leaf)
>                         goto next;
>
> -               if (!(addr & (page_size - 1)) && ((end - addr) >= page_size))
> -                       kvm_riscv_gstage_op_pte(gstage, addr, ptep,
> -                                               ptep_level, GSTAGE_OP_WP);
> -
> +               addr = ALIGN_DOWN(addr, page_size);
> +               kvm_riscv_gstage_op_pte(gstage, addr, ptep,
> +                                       ptep_level, GSTAGE_OP_WP);
>  next:
>                 addr += page_size;
>         }
> --
> 2.27.0