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[bug #38597] MTRR inconsistency between BSP and APs

From: Helge Wagner
Subject: [bug #38597] MTRR inconsistency between BSP and APs
Date: Tue, 26 Mar 2013 13:02:28 +0000
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:18.0) Gecko/20100101 Firefox/18.0


                 Summary: MTRR inconsistency between BSP and APs
                 Project: GNU GRUB
            Submitted by: helge
            Submitted on: Di 26 Mär 2013 13:02:26 GMT
                Category: Booting
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: other
         Reproducibility: Every Time
         Planned Release: None



As a BIOS/UEFI Firmware engineer I was looking through the boot log of an
OpenSuSE 12.3 system to search for error messages which might indicate
failures in our UEFI Firmware.
On our VIA based system I found this one:
"mtrr: your CPUs had inconsistent variable MTRR settings"

Further researching I found that this is caused by grub2 (the grub2 used by
OpenSuSE12.3; I am not sure which release that is): If I boot-up my OpenSuSE
through PXELINUX (just loaded kernel and initrd through tftp, the rest of the
system still on local hard disk), then the error message is gone.
Looking into the source code of grub2 I found the root cause of the problem:

"grub-core/video/i386/pc/vbe.c" has a function "grub_vbe_enable_mtrr()" which
sets a WC MTRR if the framebuffer is not already covered by a MTRR.
It does this on BSP CPU only. So after this code is run, the MTRRs between BSP
and APs are inconsistent.


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