Re: [RFC PATCH 06/11] iommu/riscv: Add domain_alloc_paging_flags for second-stage domain

[Jason Gunthorpe <jgg@ziepe.ca>]

On Tue, Apr 28, 2026 at 09:13:54PM +0800, fangyu.yu@linux.alibaba.com wrote:
> From: Fangyu Yu <fangyu.yu@linux.alibaba.com>
> 
> Replace .domain_alloc_paging with .domain_alloc_paging_flags so callers
> can pass allocation flags to select the appropriate page-table type.
> 
> When IOMMU_HWPT_ALLOC_NEST_PARENT or IOMMU_HWPT_ALLOC_DIRTY_TRACKING is
> set in @flags, allocate a second-stage (iohgatp) domain.
> 
> When @flags is 0 the behaviour is identical to the previous
> domain_alloc_paging: first-stage (iosatp) domain.
> 
> Signed-off-by: Fangyu Yu <fangyu.yu@linux.alibaba.com>
> ---
>  drivers/iommu/riscv/iommu.c | 66 ++++++++++++++++++++++++++++---------
>  1 file changed, 51 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/iommu/riscv/iommu.c b/drivers/iommu/riscv/iommu.c
> index 5dadf6d09139..0c13430ecc7f 100644
> --- a/drivers/iommu/riscv/iommu.c
> +++ b/drivers/iommu/riscv/iommu.c
> @@ -1255,23 +1255,50 @@ static const struct iommu_domain_ops riscv_iommu_paging_domain_ops = {
>  	.flush_iotlb_all = riscv_iommu_iotlb_flush_all,
>  };
>  
> -static struct iommu_domain *riscv_iommu_alloc_paging_domain(struct device *dev)
> +static struct iommu_domain *riscv_iommu_domain_alloc_paging_flags(
> +		struct device *dev, u32 flags,
> +		const struct iommu_user_data *user_data)
>  {
> +	const bool second_stage = flags &
> +		(IOMMU_HWPT_ALLOC_NEST_PARENT | IOMMU_HWPT_ALLOC_DIRTY_TRACKING);

This isn't the right logic, you should follow the switch/case design
from other drivers.

>  	struct pt_iommu_riscv_64_cfg cfg = {};
>  	struct riscv_iommu_domain *domain;
>  	struct riscv_iommu_device *iommu;
>  	int ret;
>  
> +	if (user_data)
> +		return ERR_PTR(-EOPNOTSUPP);
> +
>  	iommu = dev_to_iommu(dev);
> -	if (iommu->caps & RISCV_IOMMU_CAPABILITIES_SV57) {
> -		cfg.common.hw_max_vasz_lg2 = 57;
> -	} else if (iommu->caps & RISCV_IOMMU_CAPABILITIES_SV48) {
> -		cfg.common.hw_max_vasz_lg2 = 48;
> -	} else if (iommu->caps & RISCV_IOMMU_CAPABILITIES_SV39) {
> -		cfg.common.hw_max_vasz_lg2 = 39;
> +
> +	if (second_stage) {
> +		/*
> +		 * Second-stage (iohgatp) page table for KVM VFIO device
> +		 * pass-through and dirty tracking. The GPA space is 2 bits
> +		 * wider than the corresponding first-stage VA space (x4 root
> +		 * page table), so hw_max_vasz_lg2 values are 41/50/59.
> +		 */
> +		if (iommu->caps & RISCV_IOMMU_CAPABILITIES_SV57X4) {
> +			cfg.common.hw_max_vasz_lg2 = 59;
> +		} else if (iommu->caps & RISCV_IOMMU_CAPABILITIES_SV48X4) {
> +			cfg.common.hw_max_vasz_lg2 = 50;
> +		} else if (iommu->caps & RISCV_IOMMU_CAPABILITIES_SV39X4) {
> +			cfg.common.hw_max_vasz_lg2 = 41;
> +		} else {
> +			dev_err(dev, "cannot find supported second-stage page table mode\n");
> +			return ERR_PTR(-ENODEV);

Do not make log messages for failing system calls.

Jason