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Re: [Xen-devel] [RFC PATCH v2 00/22] xen/arm: Add ITS support

On Fri, Mar 20, 2015 at 9:53 PM, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
> Hi Vijay,
> On 19/03/2015 14:37, vijay.kilari@xxxxxxxxx wrote:
>> From: Vijaya Kumar K <Vijaya.Kumar@xxxxxxxxxxxxxxxxxx>
>> Add ITS support for arm. Following major features
>> are supported
>>   - GICv3 ITS support for arm64 platform
>>   - Supports multi ITS node
>>   - LPI descriptors are allocated on-demand
>>   - Only ITS Dom0 is supported
>> Tested with single ITS node.
> Some though about the whole design:
> Your vGIC ITS driver does too much things. In general a virtual driver
> should only emulate the hardware for the domain and forward the request to
> the physical driver.
> Your series adds device management (create/free) in the vITS, which is
> wrong.

The device is added to ITS using MAPD command. All ITS commands are based
on this device added using MAPD command. So vITS driver needs to manage

> How do you check if the domain can use the device?
> Currently, you allow any domain to use any device. That would bring a big
> mess with guest using passthrough.

ITS driver does not know which PCI device is assigned for which domain.
I think it should be done by above layers along with pci drivers in Xen.
vITS assume that the domain that sends MAPD command owns the device

> Also, does the guess will always pass the correct devid? If not how do you
> plan to handle it?

The only place it validate pci devid is vITS driver will call pci
helper function
to get ITS dt node for the BDF. Or we can add a check in MAPD command
by calling pci helper function to know if the BDF is valid or not.


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