linux-kernel - Re: [PATCH v1 07/10] iommu/vt-d: Use an xarray for global device_domain

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Message-ID: <762360b8-57ca-ab48-c454-25b9c0aec5de@linux.intel.com>
Date:   Tue, 8 Feb 2022 12:38:32 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Christoph Hellwig <hch@....de>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Liu Yi L <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 07/10] iommu/vt-d: Use an xarray for global
 device_domain_info

On 2/7/22 3:14 PM, Christoph Hellwig wrote:
>> + #define DEVI_IDX(seg, bus, devfn) ((((u16)(seg)) << 16) | PCI_DEVID(bus, devfn))
> 
> Please turn this into an real function.

Sure.

>>   /*
>> - * Iterate over elements in device_domain_list and call the specified
>> + * Iterate over elements in device_domain_array and call the specified
>>    * callback @fn against each element.
>>    */
>>   int for_each_device_domain(int (*fn)(struct device_domain_info *info,
>>   				     void *data), void *data)
>>   {
>>   	struct device_domain_info *info;
>> +	unsigned long index;
>> +	int ret = 0;
>>   
>> +	rcu_read_lock();
>> +	xa_for_each(&device_domain_array, index, info) {
>>   		ret = fn(info, data);
>> +		if (ret)
>> +			break;
>>   	}
>> +	rcu_read_unlock();
> 
> Can't we just open code this in the caller now?

That's better. I will remove this helper and make iteration in the only
caller.

> 
>>   const struct iommu_ops intel_iommu_ops;
>> @@ -900,7 +898,8 @@ static void pgtable_walk(struct intel_iommu *iommu, unsigned long pfn, u8 bus, u
>>   	struct dmar_domain *domain;
>>   	int offset, level;
>>   
>> -	info = dmar_search_domain_by_dev_info(iommu->segment, bus, devfn);
>> +	info = xa_load(&device_domain_array,
>> +		       DEVI_IDX(iommu->segment, bus, devfn));
>>   	if (!info || !info->domain) {
>>   		pr_info("device [%02x:%02x.%d] not probed\n",
>>   			bus, PCI_SLOT(devfn), PCI_FUNC(devfn));
> 
> Is there any refcounting or other life time protection for the info
> structures?

The info structure's life is managed by iommu_probe/release_device(). It
is created in probe() and freed in release().

Best regards,
baolu