linux-kernel - Re: [RFC PATCH 2/4] iommu/vt-d: Add first level page table interfaces

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Message-ID: <2755a11e-1ed0-6663-2c5b-ed50be717ba7@linux.intel.com>
Date:   Thu, 26 Sep 2019 09:42:30 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>, Peter Xu <peterx@...hat.com>
Cc:     baolu.lu@...ux.intel.com, "Raj, Ashok" <ashok.raj@...el.com>,
        Yi Sun <yi.y.sun@...ux.intel.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        David Woodhouse <dwmw2@...radead.org>
Subject: Re: [RFC PATCH 2/4] iommu/vt-d: Add first level page table interfaces

Hi Kevin,

On 9/25/19 3:32 PM, Tian, Kevin wrote:
>> From: Lu Baolu [mailto:baolu.lu@...ux.intel.com]
>> Sent: Wednesday, September 25, 2019 2:52 PM
>>
>> Hi Peter and Kevin,
>>
>> On 9/25/19 1:24 PM, Peter Xu wrote:
>>> On Wed, Sep 25, 2019 at 04:38:31AM +0000, Tian, Kevin wrote:
>>>>> From: Peter Xu [mailto:peterx@...hat.com]
>>>>> Sent: Wednesday, September 25, 2019 12:31 PM
>>>>>
>>>>> On Tue, Sep 24, 2019 at 09:38:53AM +0800, Lu Baolu wrote:
>>>>>>>> intel_mmmap_range(domain, addr, end, phys_addr, prot)
>>>>>>>
>>>>>>> Maybe think of a different name..? mmmap seems a bit weird :-)
>>>>>>
>>>>>> Yes. I don't like it either. I've thought about it and haven't
>>>>>> figured out a satisfied one. Do you have any suggestions?
>>>>>
>>>>> How about at least split the word using "_"?  Like "mm_map", then
>>>>> apply it to all the "mmm*" prefixes.  Otherwise it'll be easily
>>>>> misread as mmap() which is totally irrelevant to this...
>>>>>
>>>>
>>>> what is the point of keeping 'mm' here? replace it with 'iommu'?
>>>
>>> I'm not sure of what Baolu thought, but to me "mm" makes sense itself
>>> to identify this from real IOMMU page tables (because IIUC these will
>>> be MMU page tables).  We can come up with better names, but IMHO
>>> "iommu" can be a bit misleading to let people refer to the 2nd level
>>> page table.
>>
>> "mm" represents a CPU (first level) page table;
>>
>> vs.
>>
>> "io" represents an IOMMU (second level) page table.
>>
> 
> IOMMU first level is not equivalent to CPU page table, though you can
> use the latter as the first level (e.g. in SVA). Especially here you are
> making IOVA->GPA as the first level, which is not CPU page table.
> 
> btw both levels are for "io" i.e. DMA purposes from VT-d p.o.v. They
> are just hierarchical structures implemented by VT-d, with slightly
> different format. The specification doesn't limit how you use them for.
> In a hypothetical case, an IOMMU may implement exactly same CPU-page-
> table format and support page faults for both levels. Then you can even
> link the CPU page table to the 2nd level for sure.

Fair enough. A good conceptual gap fix.

> 
> Maybe we just name it from VT-d context, e.g. intel_map_first_level_range,
> Intel_map_second_level_range, and then register them as dmar domain
> callback as you replied in another mail.

Yes. Make sense.

> 
> Thanks
> Kevin
> 

Best regards,
Baolu