linux-kernel - Re: [PATCH 01/11] iommu/vt-d: Add pasid private data helpers

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Date:   Mon, 24 May 2021 10:16:18 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...el.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        ashok.raj@...el.com, kevin.tian@...el.com,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/11] iommu/vt-d: Add pasid private data helpers

Hi Jacob,

Thanks for reviewing my patch.

On 5/22/21 5:25 AM, Jacob Pan wrote:
> Hi BaoLu,
> 
> On Thu, 20 May 2021 11:15:21 +0800, Lu Baolu <baolu.lu@...ux.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.

The problem that this patch wants to solve is that the
iommu_sva_alloc_pasid() will attach the mm pointer to the sva pasid.

         pasid = ioasid_alloc(&iommu_sva_pasid, min, max, mm);

Assuming that each sva pasid can have only a single private data
pointer, the vendor iommu driver shouldn't set the private data again.

> 
> 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.

Yes if we have a better solution.

Best regards,
baolu