Re: [Xen-devel] Xen ARM community call - meeting minutes and date for the next one

[Pooya.Keshavarzi <Pooya.Keshavarzi@xxxxxxxxxxxx>]

Hi,

On 01/03/2017 12:33 PM, Dirk Behme wrote:
> On 20.12.2016 19:01, Julien Grall wrote:
>> Hi Andrii,
>>
>> On 20/12/2016 19:00, Andrii Anisov wrote:
>>> Sorry for the mess,
>>>
>>> I mean the xen-swiotlb issue on renesas board:
>>>
>>>> Bosch: problem with xen-swiotlb. It does not work properly on renesas
>>> board.
>>>> Stefano: please report the error on the ML
>>>>
>>>> ACTION: Bosch to send a bug report regarding xen-swiotlb
>>
>> No news so far. Dirk, do you have any update on this?
> 
> 
> We will try to update as soon as the vacation season is over, beginning of 
> next year. Together with Pooya (the Bosch guy who attended the first call) 
> I'll try to summarize the issues we see, then.
> 
> I don't have the details atm. But if I remember correctly, I've heard about 
> two (?) issues (haven't done the tests myself).
> 
> The first one was related to (e.g. USB) DMA depending how we configure the 
> memory assignments on the Renesas Salvator-X board. Depending on how much 
> memory we assign to Xen and Linux, e.g. USB wasn't working (trying to use an 
> USB stick as rootfs).
> 
> The other issue I heard about was some root file system corruptions after two 
> or three re-boots we haven't observed in the native Linux case. The plan was 
> to do some further analysis, first, before we blame Xen regarding this, 
> though.
> 
> As mentioned, Pooya will have the details and correct me if I'm totally wrong 
> here ;)
> 

Firstly sorry for the late reply on this.

Regarding the problem with swiotlb-xen here are some more details:

If we limit Dom0's memory such that only low-memory (up to 32-bit addressable 
memory) is available to Dom0, then swiotlb-xen does not have to use bounce 
buffers and the devices (e.g. USB, ethernet) would work.

But when there is some high memory also available to Dom0, the followings 
happen:
 - If the the device address happens to be in the device's DMA window (see 
xen_swiotlb_map_page()), then the device would work.
 - Otherwise if it has to allocate and map a bounce buffer, then the device 
would not work.

Kind regards,
Pooya

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