linux-kernel - Re: [PATCH v11 09/13] iommu/sva: Refactoring iommu_sva_bind/unbind

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Message-ID: <83069b7d-3dc8-8b72-246b-264389cac072@linux.intel.com>
Date:   Tue, 23 Aug 2022 18:12:44 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        Zhu Tony <tony.zhu@...el.com>, iommu@...ts.linux.dev,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v11 09/13] iommu/sva: Refactoring
 iommu_sva_bind/unbind_device()

On 2022/8/18 21:41, Jason Gunthorpe wrote:
> On Wed, Aug 17, 2022 at 09:20:20AM +0800, Lu Baolu wrote:
>> +
>> +/**
>> + * iommu_sva_bind_device() - Bind a process address space to a device
>> + * @dev: the device
>> + * @mm: the mm to bind, caller must hold a reference to mm_users
>> + *
>> + * Create a bond between device and address space, allowing the device to access
>> + * the mm using the returned PASID. If a bond already exists between @device and
>> + * @mm, it is returned and an additional reference is taken. Caller must call
>> + * iommu_sva_unbind_device() to release each reference.
>> + *
>> + * iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) must be called first, to
>> + * initialize the required SVA features.
>> + *
>> + * On error, returns an ERR_PTR value.
>> + */
>> +struct iommu_sva *iommu_sva_bind_device(struct device *dev, struct mm_struct *mm)
>> +{
>> +	struct iommu_domain *domain;
>> +	struct iommu_sva *bond;
> 
> This is called handle below, pick one name please

Updated.

> 
>> +	ioasid_t max_pasids;
>> +	int ret;
>> +
>> +	max_pasids = dev->iommu->max_pasids;
>> +	if (!max_pasids)
>> +		return ERR_PTR(-EOPNOTSUPP);
>> +
>> +	/* Allocate mm->pasid if necessary. */
>> +	ret = iommu_sva_alloc_pasid(mm, 1, max_pasids - 1);
>> +	if (ret)
>> +		return ERR_PTR(ret);
>> +
>> +	bond = kzalloc(sizeof(*bond), GFP_KERNEL);
>> +	if (!bond)
>> +		return ERR_PTR(-ENOMEM);
>> +
>> +	mutex_lock(&iommu_sva_lock);
>> +	/* Search for an existing domain. */
>> +	domain = iommu_get_domain_for_dev_pasid(dev, mm->pasid);
>> +	if (domain) {
> 
> This isn't safe, or sane. A driver could have attached something to
> this PASID that is not a SVA domain and thus not protected by the
> iommu_sva_lock.
> 
> At a minimum you should add a type match to
> iommu_get_domain_for_dev_pasid(), eg to confirm it is a SVA domain and
> do that check under the xa_lock of the pasid xarray.
> 
> And then the general idea is that SVA domain attach/detach must hold
> this janky global lock.

Make sense. I will add this logic.

> 
>> +		refcount_inc(&domain->users);
> 
> This atomic is always processed under the iommu_sva_lock, so it
> doesn't need to be an atomic anymore.

Will change it to an integer.

> 
> Otherwise this design looks OK to me too

Thank you very much for your suggestions.

Best regards,
baolu