Re: [PATCH v2 2/8] vfio/iommufd: Query dirty bitmap before DMA unmap

[Avihai Horon <avihaih@nvidia.com>]

Hi,

On 17/10/2025 11:22, Zhenzhong Duan wrote:
> External email: Use caution opening links or attachments
>
>
> When a existing mapping is unmapped, there could already be dirty bits
> which need to be recorded before unmap.
>
> If query dirty bitmap fails, we still need to do unmapping or else there
> is stale mapping and it's risky to guest.
>
> Co-developed-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> Tested-by: Xudong Hao <xudong.hao@intel.com>
> Tested-by: Giovannio Cabiddu <giovanni.cabiddu@intel.com>
> ---
>   hw/vfio/iommufd.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/hw/vfio/iommufd.c b/hw/vfio/iommufd.c
> index 976c0a8814..404e6249ca 100644
> --- a/hw/vfio/iommufd.c
> +++ b/hw/vfio/iommufd.c
> @@ -74,7 +74,13 @@ static int iommufd_cdev_unmap(const VFIOContainer *bcontainer,
>       if (iotlb && vfio_container_dirty_tracking_is_started(bcontainer)) {
>           if (!vfio_container_devices_dirty_tracking_is_supported(bcontainer) &&
>               bcontainer->dirty_pages_supported) {
> -            /* TODO: query dirty bitmap before DMA unmap */
> +            ret = vfio_container_query_dirty_bitmap(bcontainer, iova, size,
> +                                                    iotlb->translated_addr,
> +                                                    &local_err);
> +            if (ret) {
> +                error_report_err(local_err);
> +            }
> +            /* Unmap stale mapping even if query dirty bitmap fails */
>               return iommufd_backend_unmap_dma(be, ioas_id, iova, size);

If query dirty bitmap fails, shouldn't we unmap and return the query 
bitmap error to fail migration? Otherwise, migration may succeed with 
some dirtied pages not being migrated.

Thanks.

>           }
>
> --
> 2.47.1
>