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Re: [Xen-users] Enabling SMMU for a bare metal guest

On Wed, Jun 22, 2016 at 03:43:10PM +0100, Julien Grall wrote:
> Hello Jarvis,

Hi All,

> I have CCed Edgar who did the bring of Xen on Xilinx Zinqmp
> On 21/06/16 15:40, Jarvis Roach wrote:
> >I've been working on passing an ethernet controller through to a bare
> >metal guest running on an Xilinx Z US+ MPSoC platform. I got it working,
> >but only by using the system's physical address (PA) for DMA buffers and
> >descriptors instead of using the guest's intermediate physical address
> >(IPA), aka guest phyiscal address.
> >
> >I am aware of Julien's presentation on passthrough, and I am successful
> >in passing the ethernet device through to a Linux guest, but when I
> >follow the same steps for my bare metal guest, the IPA->PA translation
> >doesn't seem to be happening. I would expect that if the SMMU was active
> >for that ethernet controller then a) using PA for DMA buffers and
> >descriptors should result in a translation fault, and b) using IPA for
> >the same would work, neither of which is true.
> Can you provide the guest configuration you are using?

Jarvis, could you also provide any error messages you see or it silently
doesn't work?

Does the linux passthrough work with the exact same setup? (i.e same
board, same gem instance etc) Or are there any differences?


> >
> >It seems to me that there is something extra is being done by, or for,
> >the Linux guest that isn't done by, or for, my bare metal guest that
> >enables the SMMU for that ethernet controller. I haven't been able to
> >figure what that something extra is by searching the internet, reading
> >through the available documentation, or digging into the code. Any help
> >(better search terms, useful URLs, detailed description of the what's
> >supposed to happen for guests generically or what actually happens for a
> >Linux guest, a working bare metal example, etc) would be appreciated.
> The SMMU is configured with Stage-2 page table and not exposed to the guest.
> I am not aware of any configuration required in the guest, except having a
> working network driver.
> Regards,
> -- 
> Julien Grall

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