Re: [PATCH v2 RFC] VT-d: honor firmware-first mode in XSA-59 workaround code

[Malcolm Crossley <malcolm.crossley@citrix.com>]

On 26/05/14 11:19, Jan Beulich wrote:
> When firmware-first mode is being indicated by firmware, we shouldn't
> be modifying AER registers - these are considered to be owned by
> firmware in that case. Violating this is being reported to result in
> SMI storms. 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. Note that
> this includes a block of code enclosed in #ifdef CONFIG_X86_MCE - we
> don't define that symbol, and that code also wouldn't build without
> suitable machine check side code added; that should happen eventually,
> but isn't subject of this change.
> 
> Reported-by: Andrew Cooper <andrew.cooper3@citrix.com>
> Reported-by: Malcolm Crossley <malcolm.crossley@citrix.com>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Tested-by: Malcolm Crossley <malcolm.crossley@citrix.com>

> ---
> v2: Only check firmware-first for actual AER (i.e. ignore it for host
>     bridges in DMI mode). Use MASK_EXTR() instead of open coding it.
>     Re-word message from "cannot" to "must not".

I tested this patch on an Dell R810 BIOS version 2.7.4, it successfully
detected the firmware first mode and did not mask device 0000:00:00.0.

The other root ports already had the relevant AER errors masked.

(XEN) Must not mask UR signaling on 0000:00:00.0
(XEN) PCI add device 0000:00:00.0
(XEN) Found masked UR signaling on 0000:00:01.0
(XEN) PCI add device 0000:00:01.0
(XEN) Found masked UR signaling on 0000:00:02.0
(XEN) PCI add device 0000:00:02.0
(XEN) Found masked UR signaling on 0000:00:03.0
(XEN) PCI add device 0000:00:03.0
(XEN) Found masked UR signaling on 0000:00:05.0
(XEN) PCI add device 0000:00:05.0
(XEN) Found masked UR signaling on 0000:00:07.0
(XEN) PCI add device 0000:00:07.0
(XEN) Found masked UR signaling on 0000:00:09.0
(XEN) PCI add device 0000:00:09.0
(XEN) Masked VT-d error signaling on 0000:00:14.0

lspci -n output for Dell R810:

00:00.0 0600: 8086:3407 (rev 22)
00:01.0 0604: 8086:3408 (rev 22)
00:02.0 0604: 8086:3409 (rev 22)
00:03.0 0604: 8086:340a (rev 22)
00:05.0 0604: 8086:340c (rev 22)
00:07.0 0604: 8086:340e (rev 22)
00:09.0 0604: 8086:3410 (rev 22)
00:14.0 0800: 8086:342e (rev 22)
00:14.1 0800: 8086:3422 (rev 22)
00:14.2 0800: 8086:3423 (rev 22)