Re: PCI Pass-through in Xen ARM: Draft 4

[Julien Grall <julien.grall@citrix.com>]

Hi Manish,

I left Linaro 4 months ago. Can you please use my email citrix
(julien.grall@citrix.com).

On 13/08/15 10:42, Manish Jaggi wrote:
>  -----------------------------------------------------------------------------
> 
> 
>  1.    Background of PCI passthrough
>  -----------------------------------------------------------------------------
> 
>  Passthrough refers to assigning a PCI device to a guest domain (domU) such
>  that the guest has full control over the device. The MMIO space /
> interrupts
>  are managed by the guest itself, close to how a bare kernel manages a
> device.
> 
>  Device's access to guest address space needs to be isolated and protected.
>  SMMU (System MMU - IOMMU in ARM) is programmed by xen hypervisor to allow
>  device access guest memory for data transfer and sending MSI/X interrupts.
>  PCI devices generated message signalled interrupt writes are within guest
>  address spaces which are also translated using SMMU.

In all this design you are only speaking about MSI interrupts. But what
about legacy interrupt?

AFAICT, it's possible for Linux to use it either because MSIs are not
supported or because the user asked it.

>  4.2.2    Xenstore Update: For each PCI-EP BAR (IPA-PA mapping info).
>  ----------------------------------------------------------------------------
> 
>  Toolstack also updates the xenstore information for the device
>  (virtualbar:physical bar).This information is read by xen-pciback and
>  returned to the domU-pcifront driver configuration space reads for BAR.
> 
>  Entries created are as follows:
>  /local/domain/0/backend/pci/1/0
>  vdev-N
>      BDF = ""
>      BAR-0-IPA = ""
>      BAR-0-PA = ""
>      BAR-0-SIZE = ""
>      ...
>      BAR-M-IPA = ""
>      BAR-M-PA = ""
>      BAR-M-SIZE = ""
> 
>  Note: If BAR M SIZE is 0, it is not a valid entry.

How would you describe the ROM in xenstore?


regards,

-- 
Julien Grall