RISC-V: KVM: Fix hugepage mapping handling during dirty logging

[Anup Patel]

On Thu, Feb 26, 2026 at 2:52 PM <wang.yechao255 at zte.com.cn> wrote:
>
> From: Wang Yechao <wang.yechao255 at zte.com.cn>
>
> When dirty logging is enabled, the gstage page tables must be mapped
> at PAGE_SIZE granularity to track dirty pages accurately. Currently,
> if a huge PTE is encountered during the write-protect fault, the code
> returns -EEXIST, which breaks VM migration.
>
> Instead of returning an error, drop the huge PTE and map only the page
> that is currently being accessed. This on‑demand approach avoids the
> overhead of splitting the entire huge page into small pages upfront.
>
> Signed-off-by: Wang Yechao <wang.yechao255 at zte.com.cn>
> ---
>  arch/riscv/kvm/gstage.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kvm/gstage.c b/arch/riscv/kvm/gstage.c
> index b67d60d722c2..16c8afdafbfb 100644
> --- a/arch/riscv/kvm/gstage.c
> +++ b/arch/riscv/kvm/gstage.c
> @@ -134,7 +134,7 @@ int kvm_riscv_gstage_set_pte(struct kvm_gstage *gstage,
>
>         while (current_level != map->level) {
>                 if (gstage_pte_leaf(ptep))
> -                       return -EEXIST;
> +                       set_pte(ptep, __pte(0));

Making a leaf PTE invalid mut be followed by TLB invalidation
using gstage_tlb_flush().

I think returning -EEXIST is the right thing to do here because
caller has to split a huge PTE with proper TLB invalidation.

Regards,
Anup