Re: [PATCH v3 12/13] xen/arm: Add the property "protected-devices" in the hypervisor node

[Julien Grall <julien.grall@linaro.org>]

Hi Ian,

Sorry, I forgot to answer to this email...

On 19/03/14 10:33, Ian Campbell wrote:
> On Tue, 2014-03-18 at 20:09 +0000, Julien Grall wrote:
>> Hi Ian,
>>
>> On 03/18/2014 04:48 PM, Ian Campbell wrote:
>>> On Tue, 2014-03-11 at 15:49 +0000, Julien Grall wrote:
>>>> DOM0 is using the swiotlb to bounce DMA. With the IOMMU support in Xen,
>>>> protected devices should not use it.
>>>>
>>>> Only Xen is abled to know if an IOMMU protects the device. The new property
>>>> "protected-devices" is a list of device phandles protected by an IOMMU.
>>>>
>>>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>>>>
>>>> ---
>>>>      This patch *MUST NOT* be applied until we agreed on a device binding
>>>>      the device tree folks. DOM0 can run safely with swiotlb on protected
>>>>      devices while LVM is not used for guest disk.
>>>
>>> LVM works these days I think.
>>
>> With this patch series applied, LVM will be broken if the hard drive is
>> protected by an IOMMU.
>
> How/why?

If the guest is using LVM for its block, bouncing via the swiotlb with 
IOMMU enabled will result to wrong mapping. If I remember correctly it's 
because SWIOTLB DMA address is a physical address and not an IPA. So the 
IOMMU will rejected the request.

So we have to by-pass swiotlb in this case.

>
>> It's the case on midway, the platform will crash just after the guest
>> begins to boot.
>
> This configuration works today (osstest tests it) so this would be a
> regression. Can you sort this please?

As said above with IOMMU enabled I won't be able to sort it until my 
patch series for Linux will be upstreamed.

Regards,

-- 
Julien Grall