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

[Aravind Gopalakrishnan <aravind.gopalakrishnan@xxxxxxx>]

On 11/19/2013 10:47 AM, Jan Beulich wrote:
> > > > 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.
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..

Thanks,
Aravind.



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