linux-kernel - Re: [PATCH 04/12] iommufd: Pass parent hwpt and user_data to iommufd_hw_pagetable

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Date:   Fri, 10 Mar 2023 10:10:56 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Yi Liu <yi.l.liu@...el.com>, joro@...tes.org,
        alex.williamson@...hat.com, jgg@...dia.com, kevin.tian@...el.com,
        robin.murphy@....com
Cc:     baolu.lu@...ux.intel.com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 04/12] iommufd: Pass parent hwpt and user_data to
 iommufd_hw_pagetable_alloc()

On 3/9/23 4:09 PM, Yi Liu wrote:
> Nested translation has stage-1 and stage-2 page tables. A stage-1 page
> table is managed by user space, and it needs to work with a stage-2 page
> table, which is a parent hwpt for the stage-1 hwpt.
> 
> iommu core already supports accepting parent iommu_domain and user_data
> to allocate an iommu_domain. This makes iommufd_hw_pagetable_alloc() to
> accept the parent hwpt and user_data, and relays them to iommu core, to
> prepare for supporting hw_pagetable allocation with user_data.
> 
> Also, add a parent pointer in struct iommufd_hw_pagetable for taking and
> releasing its refcount.
> 
> Co-developed-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Nicolin Chen <nicolinc@...dia.com>
> Signed-off-by: Yi Liu <yi.l.liu@...el.com>
> ---
>   drivers/iommu/iommufd/device.c          |  2 +-
>   drivers/iommu/iommufd/hw_pagetable.c    | 28 ++++++++++++++++++++++---
>   drivers/iommu/iommufd/iommufd_private.h |  5 ++++-
>   3 files changed, 30 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c
> index 5c352807d946..19cd6df46c6a 100644
> --- a/drivers/iommu/iommufd/device.c
> +++ b/drivers/iommu/iommufd/device.c
> @@ -558,7 +558,7 @@ iommufd_device_auto_get_domain(struct iommufd_device *idev,
>   	}
>   
>   	hwpt = iommufd_hw_pagetable_alloc(idev->ictx, ioas, idev,
> -					  immediate_attach);
> +					  NULL, NULL, immediate_attach);
>   	if (IS_ERR(hwpt)) {
>   		destroy_hwpt = ERR_CAST(hwpt);
>   		goto out_unlock;
> diff --git a/drivers/iommu/iommufd/hw_pagetable.c b/drivers/iommu/iommufd/hw_pagetable.c
> index 84b4a11e62f8..16e92a1c150b 100644
> --- a/drivers/iommu/iommufd/hw_pagetable.c
> +++ b/drivers/iommu/iommufd/hw_pagetable.c
> @@ -24,6 +24,8 @@ void iommufd_hw_pagetable_destroy(struct iommufd_object *obj)
>   	if (hwpt->domain)
>   		iommu_domain_free(hwpt->domain);
>   
> +	if (hwpt->parent)
> +		refcount_dec(&hwpt->parent->obj.users);
>   	refcount_dec(&hwpt->ioas->obj.users);
>   }
>   
> @@ -46,6 +48,8 @@ int iommufd_hw_pagetable_enforce_cc(struct iommufd_hw_pagetable *hwpt)
>    * @ictx: iommufd context
>    * @ioas: IOAS to associate the domain with
>    * @idev: Device to get an iommu_domain for
> + * @parent: Optional parent HWPT to associate with the domain with
> + * @user_data: Optional user_data pointer
>    * @immediate_attach: True if idev should be attached to the hwpt
>    *
>    * Allocate a new iommu_domain and return it as a hw_pagetable. The HWPT
> @@ -54,14 +58,20 @@ int iommufd_hw_pagetable_enforce_cc(struct iommufd_hw_pagetable *hwpt)
>    */
>   struct iommufd_hw_pagetable *
>   iommufd_hw_pagetable_alloc(struct iommufd_ctx *ictx, struct iommufd_ioas *ioas,
> -			   struct iommufd_device *idev, bool immediate_attach)
> +			   struct iommufd_device *idev,
> +			   struct iommufd_hw_pagetable *parent,
> +			   void *user_data, bool immediate_attach)
>   {
>   	const struct iommu_ops *ops = dev_iommu_ops(idev->dev);
> +	struct iommu_domain *parent_domain = NULL;
>   	struct iommufd_hw_pagetable *hwpt;
>   	int rc;
>   
>   	lockdep_assert_held(&ioas->mutex);
>   
> +	if (parent && !ops->domain_alloc_user)
> +		return ERR_PTR(-EOPNOTSUPP);

My understanding here is that we are checking whether domain_alloc_user
is required. It seems that as long as the caller inputs a valid
user_data or parent, domain_alloc_user is required. If so,

	if ((user_data || parent) && !ops->domain_alloc_user)
		return ERR_PTR(-EOPNOTSUPP);

Best regards,
baolu