Re: [PATCH v2 1/3] RISC-V: KVM: Fix lost write protection on huge pages during dirty logging

[Nutty.Liu]

On 3/4/2026 5:26 PM, 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.
Would it be better to add a description of which specific commit is 
fixed  like  "Fixes: <id>..." ?

Otherwise,
Reviewed-by: Nutty Liu <nutty.liu@xxxxxxxxxxx>

Thanks,
Nutty
> Signed-off-by: Wang Yechao <wang.yechao255@xxxxxxxxxx>
> ---
>   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;
>   	}