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Date:   Fri, 21 May 2021 14:25:18 -0700
From:   Jacob Pan <jacob.jun.pan@intel.com>
To:     Lu Baolu <baolu.lu@linux.intel.com>
Cc:     Joerg Roedel <joro@8bytes.org>, <ashok.raj@intel.com>,
        <kevin.tian@intel.com>,
        Jean-Philippe Brucker <jean-philippe@linaro.org>,
        <iommu@lists.linux-foundation.org>, <linux-kernel@vger.kernel.org>,
        jacob.jun.pan@intel.com
Subject: Re: [PATCH 01/11] iommu/vt-d: Add pasid private data helpers
Message-ID: <20210521142518.25087d34@jacob-builder>
In-Reply-To: <20210520031531.712333-2-baolu.lu@linux.intel.com>
References: <20210520031531.712333-1-baolu.lu@linux.intel.com>
        <20210520031531.712333-2-baolu.lu@linux.intel.com>
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Hi BaoLu,

On Thu, 20 May 2021 11:15:21 +0800, Lu Baolu <baolu.lu@linux.intel.com>
wrote:

> We are about to use iommu_sva_alloc/free_pasid() helpers in iommu core.
> That means the pasid life cycle will be managed by iommu core. Use a
> local array to save the per pasid private data instead of attaching it
> the real pasid.
> 
I feel a little awkward to have a separate xarray for storing per IOASID
data. Seems duplicated.
Jason suggested in another thread that we can make ioasid_data public
and embeded in struct intel_svm, then we can get rid of the private data
pointer. ioasid_find will return the ioasid_data, then we can retrieve the
private data with container_of.

roughly,

struct intel_svm {
	...
	struct ioasid_data;
};

struct ioasid_data {
	ioasid_t id;
	refcount_t refs;
	struct mm_struct *mm;
};

This can be a separate patch/effort if it make sense to you.

> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> ---
>  drivers/iommu/intel/svm.c | 62 ++++++++++++++++++++++++++-------------
>  1 file changed, 41 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/iommu/intel/svm.c b/drivers/iommu/intel/svm.c
> index 5165cea90421..82b0627ad7e7 100644
> --- a/drivers/iommu/intel/svm.c
> +++ b/drivers/iommu/intel/svm.c
> @@ -17,6 +17,7 @@
>  #include <linux/dmar.h>
>  #include <linux/interrupt.h>
>  #include <linux/mm_types.h>
> +#include <linux/xarray.h>
>  #include <linux/ioasid.h>
>  #include <asm/page.h>
>  #include <asm/fpu/api.h>
> @@ -28,6 +29,23 @@ static void intel_svm_drain_prq(struct device *dev,
> u32 pasid); 
>  #define PRQ_ORDER 0
>  
> +static DEFINE_XARRAY_ALLOC(pasid_private_array);
> +static int pasid_private_add(ioasid_t pasid, void *priv)
> +{
> +	return xa_alloc(&pasid_private_array, &pasid, priv,
> +			XA_LIMIT(pasid, pasid), GFP_ATOMIC);
> +}
> +
> +static void pasid_private_remove(ioasid_t pasid)
> +{
> +	xa_erase(&pasid_private_array, pasid);
> +}
> +
> +static void *pasid_private_find(ioasid_t pasid)
> +{
> +	return xa_load(&pasid_private_array, pasid);
> +}
> +
>  int intel_svm_enable_prq(struct intel_iommu *iommu)
>  {
>  	struct page *pages;
> @@ -224,7 +242,7 @@ static int pasid_to_svm_sdev(struct device *dev,
> unsigned int pasid, if (pasid == INVALID_IOASID || pasid >= PASID_MAX)
>  		return -EINVAL;
>  
> -	svm = ioasid_find(NULL, pasid, NULL);
> +	svm = pasid_private_find(pasid);
>  	if (IS_ERR(svm))
>  		return PTR_ERR(svm);
>  
> @@ -334,7 +352,7 @@ int intel_svm_bind_gpasid(struct iommu_domain
> *domain, struct device *dev, svm->gpasid = data->gpasid;
>  			svm->flags |= SVM_FLAG_GUEST_PASID;
>  		}
> -		ioasid_set_data(data->hpasid, svm);
> +		pasid_private_add(data->hpasid, svm);
>  		INIT_LIST_HEAD_RCU(&svm->devs);
>  		mmput(svm->mm);
>  	}
> @@ -388,7 +406,7 @@ int intel_svm_bind_gpasid(struct iommu_domain
> *domain, struct device *dev, list_add_rcu(&sdev->list, &svm->devs);
>   out:
>  	if (!IS_ERR_OR_NULL(svm) && list_empty(&svm->devs)) {
> -		ioasid_set_data(data->hpasid, NULL);
> +		pasid_private_remove(data->hpasid);
>  		kfree(svm);
>  	}
>  
> @@ -431,7 +449,7 @@ int intel_svm_unbind_gpasid(struct device *dev, u32
> pasid)
>  				 * the unbind, IOMMU driver will get
> notified
>  				 * and perform cleanup.
>  				 */
> -				ioasid_set_data(pasid, NULL);
> +				pasid_private_remove(pasid);
>  				kfree(svm);
>  			}
>  		}
> @@ -547,8 +565,7 @@ intel_svm_bind_mm(struct device *dev, unsigned int
> flags, svm = kzalloc(sizeof(*svm), GFP_KERNEL);
>  		if (!svm) {
>  			ret = -ENOMEM;
> -			kfree(sdev);
> -			goto out;
> +			goto sdev_err;
>  		}
>  
>  		if (pasid_max > intel_pasid_max_id)
> @@ -556,13 +573,16 @@ intel_svm_bind_mm(struct device *dev, unsigned int
> flags, 
>  		/* Do not use PASID 0, reserved for RID to PASID */
>  		svm->pasid = ioasid_alloc(NULL, PASID_MIN,
> -					  pasid_max - 1, svm);
> +					  pasid_max - 1, NULL);
>  		if (svm->pasid == INVALID_IOASID) {
> -			kfree(svm);
> -			kfree(sdev);
>  			ret = -ENOSPC;
> -			goto out;
> +			goto svm_err;
>  		}
> +
> +		ret = pasid_private_add(svm->pasid, svm);
> +		if (ret)
> +			goto pasid_err;
> +
>  		svm->notifier.ops = &intel_mmuops;
>  		svm->mm = mm;
>  		svm->flags = flags;
> @@ -571,12 +591,8 @@ intel_svm_bind_mm(struct device *dev, unsigned int
> flags, ret = -ENOMEM;
>  		if (mm) {
>  			ret = mmu_notifier_register(&svm->notifier, mm);
> -			if (ret) {
> -				ioasid_put(svm->pasid);
> -				kfree(svm);
> -				kfree(sdev);
> -				goto out;
> -			}
> +			if (ret)
> +				goto priv_err;
>  		}
>  
>  		spin_lock_irqsave(&iommu->lock, iflags);
> @@ -590,8 +606,13 @@ intel_svm_bind_mm(struct device *dev, unsigned int
> flags, if (ret) {
>  			if (mm)
>  				mmu_notifier_unregister(&svm->notifier,
> mm); +priv_err:
> +			pasid_private_remove(svm->pasid);
> +pasid_err:
>  			ioasid_put(svm->pasid);
> +svm_err:
>  			kfree(svm);
> +sdev_err:
>  			kfree(sdev);
>  			goto out;
>  		}
> @@ -614,10 +635,8 @@ intel_svm_bind_mm(struct device *dev, unsigned int
> flags, (cpu_feature_enabled(X86_FEATURE_LA57) ?
>  						PASID_FLAG_FL5LP : 0));
>  		spin_unlock_irqrestore(&iommu->lock, iflags);
> -		if (ret) {
> -			kfree(sdev);
> -			goto out;
> -		}
> +		if (ret)
> +			goto sdev_err;
>  	}
>  	list_add_rcu(&sdev->list, &svm->devs);
>  success:
> @@ -670,6 +689,7 @@ static int intel_svm_unbind_mm(struct device *dev,
> u32 pasid) load_pasid(svm->mm, PASID_DISABLED);
>  				}
>  				list_del(&svm->list);
> +				pasid_private_remove(svm->pasid);
>  				/* We mandate that no page faults may be
> outstanding
>  				 * for the PASID when
> intel_svm_unbind_mm() is called.
>  				 * If that is not obeyed, subtle errors
> will happen. @@ -924,7 +944,7 @@ static irqreturn_t prq_event_thread(int
> irq, void *d) }
>  		if (!svm || svm->pasid != req->pasid) {
>  			rcu_read_lock();
> -			svm = ioasid_find(NULL, req->pasid, NULL);
> +			svm = pasid_private_find(req->pasid);
>  			/* It *can't* go away, because the driver is not
> permitted
>  			 * to unbind the mm while any page faults are
> outstanding.
>  			 * So we only need RCU to protect the internal
> idr code. */


Thanks,

Jacob