Re: Adding new custom devices to Xen via QEMU

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Fri, Sep 30, 2016 at 10:29:20AM -0400, Jason Dickens wrote:
> Thanks David,
> 
> This could very well be the issue, but could you please elaborate?
> The questions that come up are the following:
> What is the physical address range given to RAM? What range of addresses
> would work for my device?

I am assuming that you implemented the emulation the same way
as other devices - that is you picked an MMIO region for your
device?

> And, if this is the case, how would I unpopulate the RAM?

See xen_ram_init. But I would just choose an region that is
most definitly in MMIO (or IO) region for your emulation.

> 
> There are reasons for the address chosen, and it works on other hypervisors
> (e.g. KVM) so although it might be easiest to change the address I really

What qemu call do you use to carve out the ranges for your device?


> don't want to unless its the only way to keep from a Xen modification
> entirely.

> 
> Jason
> 
> On 9/30/2016 9:53 AM, David Vrabel wrote:
> > On 30/09/16 14:35, Jason Dickens wrote:
> > > Hi Wei,
> > > 
> > > Thanks for the response. It make sense to me that if the device were on
> > > the PCI bus (or other such bus, e.g. USB) that it could be discovered,
> > > at least by an OS. Its something to consider. I should mention that our
> > > guest VM doesn't actually use an OS.
> > > 
> > > However, the device is not implemented that as PCI it is simply memory
> > > mapped. Technically, in QEMU is has type ISA because it was derived as a
> > > modification of the TPM device. Is it possible something is lacking in
> > > the QEMU model that Xen needs but KVM doesn't?
> > > If the answer is that Xen should not need modification for any new
> > > devices then this gives me hope.  You've also inspired some things to
> > > try, like whether or not smaller modifications to the TPM device work.
> > > One change that is significant to mention is that the physical address
> > > range use is anomalous, by which I mean it not in the normal device range.
> > Does device MMIO overlap with guest RAM?  If so, you'll need to
> > unpopulate the RAM first.
> > 
> > David
> 
> 
> 
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