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Re: [Xen-devel] [PATCH 7/7] xen/arm: Blacklist some sun7i UARTs

On 27/09/13 18:02, Julien Grall wrote:
> On 09/22/2013 03:40 PM, Ian Campbell wrote:
>> On Sat, 2013-09-21 at 21:28 +0100, Julien Grall wrote:
>>> On 09/20/2013 10:41 PM, Ian Campbell wrote:
>>>> On Fri, 2013-09-20 at 20:02 +0100, Julien Grall wrote:
>>>>>> +    /*
>>>>>> +     * These UARTs share a page with the Xen console UART, so we don't
>>>>>> +     * want to map them through.
>>>>>> +     */
>>>>>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28000"),
>>>>>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28400"),
>>>>>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28800"),
>>>>>> +    DT_MATCH_PATH("/soc@01c00000/serial@01c28c00"),
>>>>> Can we blacklist all the UARTs via a DT_MATCH_COMPATIBLE? It's better
>>>>> than relying on the path that can be changed easily in the device tree.
>>>> There are other UARTS (at 0x1c29xxx) which could safely be exposed to
>>>> dom0. Perhaps it is better to just blacklist the whole lot though.
>>> These UARTs also share the same page, what prevents the user to use 
>>> these UARTs?
>> Nothing, but because they don't share a page with the xen UART they
>> don't cause it to get exposed to dom0.
> My question wasn't clear. What does prevent the user to use another UART
> for Xen?

Nothing "prevents" it.  That is the problem.  If several UARTs are on
the same page, Xen cannot safely isolate its UART from dom0/domU.


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