linux-kernel - Re: [PATCH v3 6/8] iommufd: IOPF-capable hw page table attach/detach/replace

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Date: Wed, 21 Feb 2024 14:15:24 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Joel Granados <j.granados@...sung.com>
Cc: baolu.lu@...ux.intel.com, Jason Gunthorpe <jgg@...pe.ca>,
 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>, iommu@...ts.linux.dev,
 virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 6/8] iommufd: IOPF-capable hw page table
 attach/detach/replace

On 2024/2/20 21:57, Joel Granados wrote:
>> diff --git a/drivers/iommu/iommufd/fault.c b/drivers/iommu/iommufd/fault.c
>> index e752d1c49dde..a4a49f3cd4c2 100644
>> --- a/drivers/iommu/iommufd/fault.c
>> +++ b/drivers/iommu/iommufd/fault.c
>> @@ -267,3 +267,125 @@ int iommufd_fault_iopf_handler(struct iopf_group *group)
>>   
>>   	return 0;
>>   }
>> +
>> +static void release_attach_cookie(struct iopf_attach_cookie *cookie)
>> +{
>> +	struct iommufd_hw_pagetable *hwpt = cookie->domain->fault_data;
> There is a possibility here of cookie->domain being NULL. When you call
> release_attach_cookie from iommufd_fault_domain_attach_dev if
> idev->iopf_enabled is false. In this case, you have not set the domain
> yet.

Yes. Good catch!

> 
>> +	struct iommufd_device *idev = cookie->private;
>> +
>> +	refcount_dec(&idev->obj.users);
>> +	refcount_dec(&hwpt->obj.users);
> You should decrease this ref count only if the cookie actually had a
> domain.
> 
> This function could be something like this:
> 
> 	static void release_attach_cookie(struct iopf_attach_cookie *cookie)
> 	{
> 		struct iommufd_hw_pagetable *hwpt;
> 		struct iommufd_device *idev = cookie->private;
> 
> 		refcount_dec(&idev->obj.users);
> 		if (cookie->domain) {
> 			hwpt = cookie->domain->fault_data;
> 			refcount_dec(&hwpt->obj.users);
> 		}
> 		kfree(cookie);
> 	}

Yeah, fixed.

>> +	kfree(cookie);
>> +}
>> +
>> +static int iommufd_fault_iopf_enable(struct iommufd_device *idev)
>> +{
>> +	int ret;
>> +
>> +	if (idev->iopf_enabled)
>> +		return 0;
>> +
>> +	ret = iommu_dev_enable_feature(idev->dev, IOMMU_DEV_FEAT_IOPF);
>> +	if (ret)
>> +		return ret;
>> +
>> +	idev->iopf_enabled = true;
>> +
>> +	return 0;
>> +}
>> +
>> +static void iommufd_fault_iopf_disable(struct iommufd_device *idev)
>> +{
>> +	if (!idev->iopf_enabled)
>> +		return;
>> +
>> +	iommu_dev_disable_feature(idev->dev, IOMMU_DEV_FEAT_IOPF);
>> +	idev->iopf_enabled = false;
>> +}
>> +
>> +int iommufd_fault_domain_attach_dev(struct iommufd_hw_pagetable *hwpt,
>> +				    struct iommufd_device *idev)
>> +{
>> +	struct iopf_attach_cookie *cookie;
>> +	int ret;
>> +
>> +	cookie = kzalloc(sizeof(*cookie), GFP_KERNEL);
>> +	if (!cookie)
>> +		return -ENOMEM;
>> +
>> +	refcount_inc(&hwpt->obj.users);
>> +	refcount_inc(&idev->obj.users);
>> +	cookie->release = release_attach_cookie;
>> +	cookie->private = idev;
>> +
>> +	if (!idev->iopf_enabled) {
>> +		ret = iommufd_fault_iopf_enable(idev);
>> +		if (ret)
>> +			goto out_put_cookie;
> You have not set domain here and release_attach_cookie will try to
> access a null address.

Fixed as above.

Best regards,
baolu