Re: [Xen-devel] [PATCH V2] ns16550: Add support for UART present in Broadcom TruManage capable NetXtreme chips

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 19.11.13 at 17:40, Aravind Gopalakrioshnan 
>>> <aravind.gopalakrishnan@xxxxxxx> wrote:
> On 11/18/2013 2:04 AM, Jan Beulich wrote:
>> But then you'd need to carefully consider what the remainder of
>> the MMIO range is used for - if any of that could conflict with
>> what Xen needs to fully control the device, then you should also
>> hide any PAGE_SIZE chunks from all domains (including Dom0).
>> (Unfortunately we can't currently hide sub-page chunks in an
>> effective manner.)
> 
> With respect to this,
> I am not seeing any untoward side effects to Xen from letting the code 
> run as-is.
> I have tested the patch with the Broadcom 5725 UART chip and a IO based 
> UART as well
> and both seem to function fine..

Sure, because you surely used a well behaved Dom0. But you
should (a) protect Xen from a bug in Dom0 and (b) either prevent
the device from being assigned to a guest, or make sure a
malicious guest can't interfere with Xen's operation.

> I did try using 'iomem_deny_access' to hide the MMIO range from dom0. 
> But I don't see an effect.
> Not sure if I am missing something or is there a different way to hide 
> PAGE_SIZE chunks?

No, what you say you did is correct afaict.

Jan


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