linux-kernel - Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

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Date:   Fri, 4 Aug 2023 11:26:50 +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>,
        "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>
Subject: Re: [PATCH v2 08/12] iommu: Prepare for separating SVA and IOPF

On 2023/8/3 16:16, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Thursday, July 27, 2023 1:49 PM
>>
>> @@ -82,7 +82,7 @@ static void iopf_handler(struct work_struct *work)
>>   	if (!domain || !domain->iopf_handler)
>>   		status = IOMMU_PAGE_RESP_INVALID;
>>
>> -	list_for_each_entry_safe(iopf, next, &group->faults, list) {
>> +	list_for_each_entry(iopf, &group->faults, list) {
>>   		/*
>>   		 * For the moment, errors are sticky: don't handle
>> subsequent
>>   		 * faults in the group if there is an error.
>> @@ -90,14 +90,20 @@ static void iopf_handler(struct work_struct *work)
>>   		if (status == IOMMU_PAGE_RESP_SUCCESS)
>>   			status = domain->iopf_handler(&iopf->fault,
>>   						      domain->fault_data);
>> -
>> -		if (!(iopf->fault.prm.flags &
>> -		      IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE))
>> -			kfree(iopf);
>>   	}
>>
>>   	iopf_complete_group(group->dev, &group->last_fault, status);
>> -	kfree(group);
>> +	iopf_free_group(group);
>> +}
> 
> this is perf-critical path. It's not good to traverse the list twice.

Freeing the fault group is not critical anymore, right?

> 
>> +
>> +static int iopf_queue_work(struct iopf_group *group, work_func_t func)
>> +{
>> +	struct iopf_device_param *iopf_param = group->dev->iommu-
>>> iopf_param;
>> +
>> +	INIT_WORK(&group->work, func);
>> +	queue_work(iopf_param->queue->wq, &group->work);
>> +
>> +	return 0;
>>   }
> 
> Is there plan to introduce further error in the future? otherwise this should
> be void.

queue_work() return true or false. I should check and return the value.

> 
> btw the work queue is only for sva. If there is no other caller this can be
> just kept in iommu-sva.c. No need to create a helper.

The definition of struct iopf_device_param is in this file. So I added a
helper to avoid making iopf_device_param visible globally.

> 
>> @@ -199,8 +204,11 @@ int iommu_queue_iopf(struct iommu_fault *fault,
>> struct device *dev)
>>   			list_move(&iopf->list, &group->faults);
>>   	}
>>
>> -	queue_work(iopf_param->queue->wq, &group->work);
>> -	return 0;
>> +	ret = iopf_queue_work(group, iopf_handler);
>> +	if (ret)
>> +		iopf_free_group(group);
>> +
>> +	return ret;
>>
> 
> Here we can document that the iopf handler (in patch10) should free the
> group, allowing the optimization inside the handler.

Yeah!

Best regards,
baolu