Re: Buggy IOMMU support in Coreboot on Chromebook Pixel 2 i7-5600U

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

On 15/08/15 06:14, fowlslegs@riseup.net wrote:
> On 2015-08-14 01:41, Andrew Cooper wrote:
>> On 14/08/15 08:13, fowlslegs@riseup.net wrote:
>>> On the VT-d troubleshooting page, I was informed to shoot you all a 
>>> message if Xen had to deactivate my VT-d due to errors in my BIOS 
>>> (in this case Coreboot). I am running John Lewis' Coreboot ROM for 
>>> the Chromebook Pixel 2 (samus) w/ the i7-5600U processor and Xen 
>>> 4.4.2 on Qubes. I downloaded and cracked open (for lack of better 
>>> words) John Lewis's Coreboot image (which is a modified version of 
>>> the one in the Google repos) and found that src/arch/x86/acpi.c had 
>>> the same section added by the http://review.coreboot.org/#/c/1654/ 
>>> commit written by Patrick Georgi a few years back that is supposed 
>>> to provide ACPI DMAR tables. The problem might just be the code is 
>>> out of date for modern processors or maybe it has just not been 
>>> tested against many CPUs.
>>>
>>> It does appear that there has been changes to this acpi.c file in 
>>> the Coreboot master branch, which makes me wonder if building 
>>> against that would fix my problems. Realistically though, I have 
>>> barely any experience or knowledge with Coreboot hacking and I'm 
>>> assuming there is a web of dependencies that I couldn't figure out 
>>> without possibly months of research, trial, and error.
>>>
>>> Anyway, just wanted to send in this report as maybe you don't get 
>>> too many involving Coreboot and maybe you might find it interesting 
>>> or in the minute chance you might be able to help me out. Anyway, 
>>> here's the output of `xl dmesg`:
>>
>> Please reboot and use "iommu=verbose,debug" on the Xen command line,
>> which will offer more information.
>>
>> ~Andrew
>>
>
> I was already passing iommu=verbose, but not debug as well. Here is 
> the new log

Not the one you posted.  Line 4 prints the full command line as passed 
to Xen.  Anyhow, ...

>
>  Xen 4.4.2-6.fc20
> (XEN) Xen version 4.4.2 (user@) (gcc (GCC) 4.8.3 20140911 (Red Hat 
> 4.8.3-7)) debug=n Thu Jul 23 20:12:15 UTC 2015
> (XEN) Latest ChangeSet:
> (XEN) Bootloader: GRUB 2.00
> (XEN) Command line: placeholder console=none dom0_mem=min:1024M 
> iommu=verbose,debug
> (XEN) Video information:
> (XEN)  VGA is text mode 80x25, font 8x16
> (XEN) Disc information:
> (XEN)  Found 2 MBR signatures
> (XEN)  Found 2 EDD information structures
> (XEN) Xen-e820 RAM map:
> (XEN)  0000000000000000 - 000000000009fc00 (usable)
> (XEN)  000000000009fc00 - 00000000000a0000 (reserved)
> (XEN)  00000000000f0000 - 0000000000100000 (reserved)
> (XEN)  0000000000100000 - 000000007ce27000 (usable)
> (XEN)  000000007ce27000 - 0000000080000000 (reserved)
> (XEN)  00000000f0000000 - 00000000f4000000 (reserved)
> (XEN)  00000000fed10000 - 00000000fed1a000 (reserved)
> (XEN)  00000000fed40000 - 00000000fed45000 (reserved)
> (XEN)  00000000fed80000 - 00000000fed85000 (reserved)
> (XEN)  0000000100000000 - 000000047f000000 (usable)
> (XEN) ACPI: RSDP 000F2760, 0024 (r2 CORE  )
> (XEN) ACPI: XSDT 7CF440E0, 004C (r1 CORE   COREBOOT        0 
> CORE        0)
> (XEN) ACPI: FACP 7CF48970, 00F4 (r5 CORE   COREBOOT        0 
> CORE        1)
> (XEN) ACPI: DSDT 7CF44250, 4720 (r2 COREv4 COREBOOT 20110725 INTL 
> 20130117)
> (XEN) ACPI: FACS 7CF44210, 0040
> (XEN) ACPI: HPET 7CF48A70, 0038 (r1 CORE   COREBOOT        0 
> CORE        0)
> (XEN) ACPI: APIC 7CF48AB0, 006C (r1 CORE   COREBOOT        0 
> CORE        0)
> (XEN) ACPI: MCFG 7CF48B20, 003C (r1 CORE   COREBOOT        0 
> CORE        0)
> (XEN) ACPI: SSDT 7CF49BC0, 0FF8 (r2 CORE   COREBOOT       2A 
> CORE       2A)
> (XEN) System RAM: 16317MB (16709400kB)

... there is no DMAR table, which means that coreboot has not told Xen 
that an IOMMU exists on the system.

~Andrew

<snip>