Re: Xen 4.2.1 boot failure with IOMMU enabled

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 02/14/2013 06:29 AM, Jan Beulich wrote:
>>>> On 13.02.13 at 19:21, povder <povder@gmail.com> wrote:
>> I don't see 06:00.1 device in IOMMU enabling process on which Xen crashes.
>>
>> lspci output: http://pastebin.com/raw.php?i=3wpKPQT9
> This is really odd: The "iommu=debug" output you made available
> shows that while there are further devices that have no associated
> IOMMU, the bus scan done in the hypervisor didn't even find a
> device at 06:00.1. Which I see possible only in two ways: Either
> the device becomes visible on the bus only when the driver for
> 06:00.0 loads (and is otherwise detectable only by other means,
> e.g. ACPI), or 06:00.0 doesn't have the multi function device flag
> properly set. That latter aspect could be checked by looking at
> the raw (hex) config space dump of 06:00.0.

If I read this correctly, Linux enables multi-functionness (?):

http://lxr.linux.no/#linux+v3.7.7/drivers/pci/quirks.c#L1494

So you are probably right. BIOS does not enumerate 06:00.1 in IVRS because
it doesn't see it enabled yet.

>
> Boris, one other thought I had in this context: Is it really possible
> for functions on the same (non-bridge) device to be serviced
> by different IOMMUs?

I can't see how this may be possible: IOMMU is PCIe root complex and any
downstream device can only send transactions through its root. (I hope I am
using right terminology).

> If not, find_iommu_for_device() could simply
> look for function 0 if nothing is known about the passed in function.

Yes, this could work. But with a warning in the log.

-boris