linux-kernel - Re: [PATCH v4 2/9] iommu: Replace sva_iommu with iommu_attach

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Date: Wed, 10 Apr 2024 14:12:22 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.com>,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>, Yi Liu <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joel Granados <j.granados@...sung.com>, iommu@...ts.linux.dev,
 virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/9] iommu: Replace sva_iommu with iommu_attach_handle

On 4/10/24 7:48 AM, Jason Gunthorpe wrote:
> On Tue, Apr 09, 2024 at 10:11:28AM +0800, Baolu Lu wrote:
>> On 4/8/24 10:19 PM, Jason Gunthorpe wrote:
>>> On Sat, Apr 06, 2024 at 02:09:34PM +0800, Baolu Lu wrote:
>>>> On 4/3/24 7:59 PM, Jason Gunthorpe wrote:
>>>>> On Wed, Apr 03, 2024 at 09:15:12AM +0800, Lu Baolu wrote:
>>>>>> +	/* A bond already exists, just take a reference`. */
>>>>>> +	handle = iommu_attach_handle_get(group, iommu_mm->pasid);
>>>>>> +	if (handle) {
>>>>>> +		mutex_unlock(&iommu_sva_lock);
>>>>>> +		return handle;
>>>>>>     	}
>>>>> At least in this context this is not enough we need to ensure that the
>>>>> domain on the PASID is actually an SVA domain and it was installed by
>>>>> this mechanism, not an iommufd domain for instance.
>>>>>
>>>>> ie you probably need a type field in the iommu_attach_handle to tell
>>>>> what the priv is.
>>>>>
>>>>> Otherwise this seems like a great idea!
>>>> Yes, you are right. For the SVA case, I will add the following changes.
>>>> The IOMMUFD path will also need such enhancement. I will update it in
>>>> the next version.
>>> The only use for this is the PRI callbacks right? Maybe instead of
>>> adding a handle type let's just check domain->iopf_handler  ?
>>>
>>> Ie SVA will pass &ommu_sva_iopf_handler as its "type"
>> Sorry that I don't fully understand the proposal here.
> I was talking specifically about the type field you suggested adding
> to the handle struct.
> 
> Instead of adding a type field check the domain->iopf_handler to
> determine the domain and thus handle type.
> 
>> The problem is that the context code (SVA, IOMMUFD, etc.) needs to make
>> sure that the attach handle is really what it has installed during
>> domain attachment. The context code needs some mechanism to include some
>> kind of "owner cookie" in the attach handle, so that it could check
>> against it later for valid use.
> Right, you have a derived struct for each user and you need a way to
> check if casting from the general handle struct to the derived struct
> is OK.
> 
> I'm suggesting using domain->iopf_handle as the type key.

Oh, I see. It works. Thanks!

Best regards,
baolu