linux-kernel - Re: [PATCH v11 12/16] iommu: Use refcount for fault data access

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Date: Mon, 5 Feb 2024 19:46:46 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>
Cc: baolu.lu@...ux.intel.com, "Liu, Yi L" <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Longfang Liu <liulongfang@...wei.com>, "Zhao, Yan Y" <yan.y.zhao@...el.com>,
 Joel Granados <j.granados@...sung.com>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v11 12/16] iommu: Use refcount for fault data access

On 2024/2/5 16:37, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Tuesday, January 30, 2024 4:09 PM
>>
>> The per-device fault data structure stores information about faults
>> occurring on a device. Its lifetime spans from IOPF enablement to
>> disablement. Multiple paths, including IOPF reporting, handling, and
>> responding, may access it concurrently.
>>
>> Previously, a mutex protected the fault data from use after free. But
>> this is not performance friendly due to the critical nature of IOPF
>> handling paths.
>>
>> Refine this with a refcount-based approach. The fault data pointer is
>> obtained within an RCU read region with a refcount. The fault data
>> pointer is returned for usage only when the pointer is valid and a
>> refcount is successfully obtained. The fault data is freed with
>> kfree_rcu(), ensuring data is only freed after all RCU critical regions
>> complete.
>>
>> An iopf handling work starts once an iopf group is created. The handling
>> work continues until iommu_page_response() is called to respond to the
>> iopf and the iopf group is freed. During this time, the device fault
>> parameter should always be available. Add a pointer to the device fault
>> parameter in the iopf_group structure and hold the reference until the
>> iopf_group is freed.
>>
>> Make iommu_page_response() static as it is only used in io-pgfault.c.
>>
>> Co-developed-by: Jason Gunthorpe <jgg@...dia.com>
>> Signed-off-by: Jason Gunthorpe <jgg@...dia.com>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
>> Tested-by: Yan Zhao <yan.y.zhao@...el.com>
> 
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> 
>>    * struct iommu_fault_param - per-device IOMMU fault data
>>    * @lock: protect pending faults list
>> + * @users: user counter to manage the lifetime of the data
>> + * @ruc: rcu head for kfree_rcu()
> 
> s/ruc/rcu

Fixed. Thank you!

Best regards,
baolu