linux-kernel - Re: [PATCH v2 7/7] iommu/vt-d: Remove lazy allocation of domains

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Message-Id: <48D45E21-9B4B-40AB-A698-5386E08A6646@arista.com>
Date:   Fri, 22 Mar 2019 10:07:01 +0000
From:   James Sewart <jamessewart@...sta.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org, Tom Murphy <tmurphy@...sta.com>,
        Dmitry Safonov <dima@...sta.com>, linux-kernel@...r.kernel.org,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [PATCH v2 7/7] iommu/vt-d: Remove lazy allocation of domains

Hey Jacob,

> On 14 Mar 2019, at 23:35, Jacob Pan <jacob.jun.pan@...ux.intel.com> wrote:
> 
> On Thu, 14 Mar 2019 11:59:36 +0000
> James Sewart <jamessewart@...sta.com> wrote:
> 
>> 
>> -	domain = get_valid_domain_for_dev(dev);
>> +	domain = find_domain(dev);
>> 	if (!domain)
>> 		return DMA_MAPPING_ERROR;
>> 
>> @@ -3914,7 +3624,7 @@ static int intel_map_sg(struct device *dev,
>> struct scatterlist *sglist, int nele if (iommu_no_mapping(dev))
>> 		return intel_nontranslate_map_sg(dev, sglist,
>> nelems, dir); 
>> -	domain = get_valid_domain_for_dev(dev);
>> +	domain = find_domain(dev);
> This patchset looks like a very good clean up, I am wondering why we
> can't use the generic iommu_get_domain_for_dev() here, since VT-d has a
> default DMA domain after your patch.

This should be possible, only downside is we get an iommu_domain from 
iommu_get_domain_for_dev and will have to check its not null before 
getting the dmar_domain from it. We will be able to remove find_domain 
though.

Cheers,
James.