Re: [PATCH RFC] VT-d: honor firmware-first mode in XSA-59 workaround code

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 21/05/14 17:09, Jan Beulich wrote:
> When firmware-first mode is being indicated by firmware, we shouldn't
> be modifying AER registers - these ar considered to be owned by

"these are"

> firmware in that case. Violating this is being reported to result in
> SMI (or was it SCI?) storms.

SMM livelock.

The exact problem was a 2.6.32 kernel ignoring firmware-first and
disabling reporting on the root ports but not endpoint devices, causing
the SMM handler to fail to find the issue, and fail to clear the SMI.

However, as part of the investigation, we identified that Xen was also
violating firmware-first as part of XSA-59

~Andrew

>  While circumventing the workaround means
> re-exposing affected hosts to the XSA-59 issues, this in any event
> seems better than not booting at all. Respective messages are being
> issued to the log, so the situation can be diagnosed.
>
> The basic building blocks were taken from Linux 3.15-rc.
>
> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Reported-by: Malcolm Crossley <malcolm.crossley@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>