[vfio-users] Ryzen/X370 Chipset and IOMMU Groups

[Alex Williamson]

On Thu, Mar 9, 2017 at 12:33 AM, Nick Sarnie <commendsarnex at gmail.com>
wrote:

> I expect Alex to find it's a BIOS bug. Also, the ACS patch does allow the
> groups to be made separating the GPUs(Wendell reported it didn't work), but
> I haven't gotten around to testing actual passthrough to see if there's
> some other issue(Maybe this is what he meant). I'll report if it works
> tomorrow.
>

What evidence do you have to suggest a BIOS bug?  ACS is a hardware
feature, so the only way I can imagine a BIOS bug being a factor is if the
BIOS has some ability to disable it by dropping it from the capability
chain.  If you add one more 'x' to make it lspci -xxxx then we can see the
raw dump of the extended capability space, though ACS is a tiny capability,
it might be impossible to positively identify it if the capability ID is
masked.  My guess is that it's either an oversight or marketing distinction
reserved for their server lines (we'll see once those ship), and that maybe
we can work with them to create quirks to expose isolation if it exists.
I've already started reaching out to AMD for this.  Thanks,

Alex
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