linux-kernel - Re: [PATCH 9/9] iommu: Use fault cookie to store iopf

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Date:   Wed, 12 Jul 2023 11:09:25 +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 9/9] iommu: Use fault cookie to store iopf_param

On 2023/7/11 14:26, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>> Sent: Tuesday, July 11, 2023 9:07 AM
>>
>> Remove the static iopf_param pointer from struct iommu_fault_param to
>> save memory.
> 
> why is there memory saving? you replace a single pointer with a xarray now...

iopf_param is duplicate with the fault cookie. So replace it with the
fault cookie to remove duplication and save memory.

> 
>> @@ -303,16 +303,27 @@ int iopf_queue_add_device(struct iopf_queue
>> *queue, struct device *dev)
>>
>>   	mutex_lock(&queue->lock);
>>   	mutex_lock(&param->lock);
>> -	if (!param->iopf_param) {
>> -		list_add(&iopf_param->queue_list, &queue->devices);
>> -		param->iopf_param = iopf_param;
>> -		ret = 0;
>> +	curr = iommu_set_device_fault_cookie(dev, 0, iopf_param);
>> +	if (IS_ERR(curr)) {
>> +		ret = PTR_ERR(curr);
>> +		goto err_free;
>>   	}
> 
> So although the new xarray is called a per-pasid storage, here only
> slot#0 is used for sva which includes a list containing partial req's
> for many pasid's. It doesn't sound clean...

Just to make it generic so that IOMMUFD can also use it. IOMMUFD will
use it to store the per-{device, pasid} object id (and possibly other
data) so that it can be quickly retrieved in the critical fault
delivering patch.

Best regards,
baolu