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

On 11/19/2013 10:47 AM, Jan Beulich wrote:
On 19.11.13 at 17:40, Aravind Gopalakrioshnan <aravind.gopalakrishnan@xxxxxxx> 
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.

Looks like the arguments I was passing in to 'iomem_deny_access' was incorrect before (apologies)
(I just had to use paddr_to_pfn() to get PAGE_SHIFT-ed value)
I tried with the proper (page shifted) values, but it breaks Xen throwing the message:

(XEN) mm.c:785:d0 Non-privileged (0) attempt to map I/O space

The reason for this is - dom0 sees the UART device and tries to configure it at the bar value (which is blocked by Xen) which means pci_hide_device() is not functioning as expected..(again, not sure if I am missing something..). But- Could this be due to the fact that this is a multifunction device and the UART is only a subfunction?

Meanwhile, I am sending a V3 with the other changes..


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