Re: [Xen-devel] [PATCH V2 9/25] tools/libxl: build DMAR table for a guest with one virtual VTD

[Lan Tianyu <tianyu.lan@xxxxxxxxx>]

On 2017年08月23日 16:34, Wei Liu wrote:
> On Wed, Aug 23, 2017 at 01:35:17PM +0800, Lan Tianyu wrote:
>> On 2017年08月22日 21:48, Wei Liu wrote:
>>>>> Hi, Wei
>>>>> Thanks for your comments.
>>>>>
>>>>> iirc, HVM only supports one module; DMAR cannot be a new module. Joining 
>>>>> to
>>>>> the existing one is the approach we are taking. 
>>>>>
>>>>> Which kind of conflicts you think should be resolved? If you mean I
>>>>> forget to free the old buf, I will fix this. If you mean the potential
>>>>> overlap between the binary passed by admin and DMAR table built here, I
>>>>> don't have much idea on this. Even without the DMAR table, the binary
>>>>> may contains MADT or other tables and tool stacks don't intrepret the
>>>>> binary and check whether there are conflicts, right?
>>>>>
>>> Thinking a bit more about this, when I first said "conflicts" I didn't
>>> mean to parse the content. I was referring to the code in
>>> libxl_x86_apci.c which also seems to manipulate acpi_modules.
>>
>> Code in libxl_x86_acpi.c works for Hvmlite/PVHv2. The code we added is
>> for hvm guest.
>>
> 
> That's correct for the code as-is but what is preventing the code there
> from working with HVM? Assuming correct checks and branches are added
> to appropriate places?
> 
> I'm against having multiple locations doing things that could
> potentially clash with each other. In the foreseeable future PVH is
> going to get need similar functionality.
> 
> My expectation is that if the existing code needs to be taken into
> consideration and the contributors need to figure out if and how it can
> be modified to suite their needs. If everyone is doing their own thing
> in their own little function Xen will eventually become unmaintainable.
> 
>>>
>>> I would like the code to generate dmar take into consideration
>>> libxl__dom_load_acpi.
>>>
>>
>> If add dmar table for hvmlite, we should combine dmar table with other
>> ACPI table and populate into acpi_modules[2]. This is how hvmlite add
>> other ACPI tables in libxl__dom_load_acpi().
>>
> 
> Sure, that sounds plausible.
> 
> What I would like to see is to have one entry point to manipulate APCI
> tables.
> 
> Given the patch volume we're seeing now, we expect contributors to drive
> the discussion forward. If you're not sure, feel free to ask more questions.

I am not sure whether I understood correctly.

PVHv2 builds all ACPI table in tool stack and uses acpi_module[0, 1, 2]
to pass related table content.

HVM builds ACPI tables in hvmloader and just use acpi_module[0] to pass
additional ACPI firmware or table.

These two modes have different way to use acpi_modules[]. So I think we
can't combine them, right?

For build dmar table, we have introduced construct_dmar() in under
libacpi to build dmar table and PVHv2 also can use it in
libxl__dom_load_acpi().


-- 
Best regards
Tianyu Lan

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