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Re: Missing memory and the mystery of MTRRs

From "Alexander V. Makartsev" <avbetev@gmail.com>
Newsgroups linux.debian.user
Subject Re: Missing memory and the mystery of MTRRs
Date 2021-02-14 11:50 +0100
Message-ID <BIn8t-Dq-5@gated-at.bofh.it> (permalink)
References <BIaXE-1Mb-13@gated-at.bofh.it>
Organization linux.* mail to news gateway

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On 14.02.2021 02:17, Charlie Gibbs wrote:
> [This would probably be an FAQ if I knew the proper incantation...]
>
> I realized recently that a box I've been running for a while isn't 
> seeing all of its installed memory.  The BIOS screens indicate that 
> 8GB is installed, but Debian (recently upgraded to Buster) only sees a 
> bit over 3GB.
>
> cjg@dragon:~$ head -1 /proc/meminfo
> MemTotal:        3331096 kB
>
> During boot I noticed the following message:
>
> [    0.012080] WARNING: BIOS bug: CPU MTRRs don't cover all of memory, 
> losing 4800MB of RAM.
>
> So I guess it's time to start learning about the wonderful world of 
> MTRRs.
>
> cjg@dragon:~$ cat /proc/mtrr
> reg00: base=0x000000000 (    0MB), size= 2048MB, count=1: write-back
> reg01: base=0x080000000 ( 2048MB), size= 1024MB, count=1: write-back
> reg02: base=0x0c0000000 ( 3072MB), size=  256MB, count=1: write-back
> reg03: base=0x0cff00000 ( 3327MB), size=    1MB, count=1: uncachable
>
> cjg@dragon:~$ head -9 /proc/cpuinfo
> processor    : 0
> vendor_id    : GenuineIntel
> cpu family    : 6
> model        : 15
> model name    : Intel(R) Core(TM)2 CPU          6300  @ 1.86GHz
> stepping    : 2
> microcode    : 0x56
> cpu MHz        : 1598.388
> cache size    : 2048 KB
>
> Here's the first part of /var/log/messages:
>
> [    0.000000] Linux version 4.19.0-6-amd64 
> (debian-kernel@lists.debian.org) (gcc version 8.3.0 (Debian 8.3.0-6)) 
> #1 SMP Debian 4.19.67-2+deb10u1 (2019-09-20)
> [    0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-4.19.0-6-amd64 
> root=UUID=4d3143dd-d732-4755-b832-05753ab9c53a ro quiet
> [    0.000000] x86/fpu: x87 FPU will use FXSAVE
> [    0.000000] BIOS-provided physical RAM map:
> [    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000008efff] 
> usable
> [    0.000000] BIOS-e820: [mem 0x000000000008f000-0x000000000009ffff] 
> reserved
> [    0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff] 
> reserved
> [    0.000000] BIOS-e820: [mem 0x0000000000100000-0x00000000cfd60fff] 
> usable
> [    0.000000] BIOS-e820: [mem 0x00000000cfd61000-0x00000000cfd6dfff] 
> reserved
> [    0.000000] BIOS-e820: [mem 0x00000000cfd6e000-0x00000000cfe1efff] 
> usable
> [    0.000000] BIOS-e820: [mem 0x00000000cfe1f000-0x00000000cfee8fff] 
> ACPI NVS
> [    0.000000] BIOS-e820: [mem 0x00000000cfee9000-0x00000000cfeecfff] 
> usable
> [    0.000000] BIOS-e820: [mem 0x00000000cfeed000-0x00000000cfef1fff] 
> ACPI data
> [    0.000000] BIOS-e820: [mem 0x00000000cfef2000-0x00000000cfef2fff] 
> usable
> [    0.000000] BIOS-e820: [mem 0x00000000cfef3000-0x00000000cfefefff] 
> ACPI data
> [    0.000000] BIOS-e820: [mem 0x00000000cfeff000-0x00000000cfefffff] 
> usable
> [    0.000000] BIOS-e820: [mem 0x00000000cff00000-0x00000000cfffffff] 
> reserved
> [    0.000000] BIOS-e820: [mem 0x00000000fff00000-0x00000000ffffffff] 
> reserved
> [    0.000000] BIOS-e820: [mem 0x0000000100000000-0x000000022bffffff] 
> usable
> [    0.000000] NX (Execute Disable) protection: active
> [    0.000000] SMBIOS 2.4 present.
> [    0.000000] DMI:  /DG965WH, BIOS MQ96510J.86A.1687.2007.0510.0258 
> 05/10/2007
> [    0.000000] tsc: Fast TSC calibration using PIT
> [    0.000000] tsc: Detected 1864.782 MHz processor
> [    0.011112] e820: update [mem 0x00000000-0x00000fff] usable ==> 
> reserved
> [    0.011115] e820: remove [mem 0x000a0000-0x000fffff] usable
> [    0.011126] last_pfn = 0x22c000 max_arch_pfn = 0x400000000
> [    0.011134] MTRR default type: uncachable
> [    0.011135] MTRR fixed ranges enabled:
> [    0.011137]   00000-9FFFF write-back
> [    0.011139]   A0000-FFFFF uncachable
> [    0.011140] MTRR variable ranges enabled:
> [    0.011142]   0 base 000000000 mask F80000000 write-back
> [    0.011144]   1 base 080000000 mask FC0000000 write-back
> [    0.011145]   2 base 0C0000000 mask FF0000000 write-back
> [    0.011147]   3 base 0CFF00000 mask FFFF00000 uncachable
> [    0.011148]   4 disabled
> [    0.011149]   5 disabled
> [    0.011149]   6 disabled
> [    0.011150]   7 disabled
> [    0.011968] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB WP  
> UC- WT
> [    0.012074] e820: update [mem 0xcff00000-0x22bffffff] usable ==> 
> reserved
> [    0.012080] WARNING: BIOS bug: CPU MTRRs don't cover all of memory, 
> losing 4800MB of RAM.
>
> Is there some sort of HOWTO that covers this stuff?  Where do I go 
> from here?
>
Even if there is a "HOWTO" to learn some information, are you capable of 
unpacking, disassembling and patching BIOS of your motherboard and 
reassemble working image of it to flash into ROM?

I suggest you to fiddle with BIOS settings first. Search for anything 
that looks like memory related, like "Memory Hole", or something.
If this trial and error approach won't help, you can update your BIOS as 
a last resort.
Since your motherboard is pretty old, and Intel has dropped all support 
for Legacy products, you can't download BIOS updates from Intel official 
source anymore. [1]
But you can still find them on archive sites. [2] I can't vouch for this 
site, but it looks like genuine BIOS update from Intel.
I have to warn you about security risks, because there could be a small 
possibility, it was patched with malware, but considering this BIOS is 
for an ancient hardware I have my doubts and personally I would take the 
risk.
And besides, there are no other options.


[1] 
https://www.intel.com/content/www/us/en/support/products/22639/boards-and-kits/desktop-boards/legacy-intel-desktop-boards/intel-desktop-board-dg965wh.html
[2] https://driverscollection.com/?H=DG965WH&By=INTEL&SS=BIOS

-- 
With kindest regards, Alexander.

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⢿⡄⠘⠷⠚⠋⠀ https://www.debian.org
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Thread

Missing memory and the mystery of MTRRs Charlie Gibbs <cgibbs@surfnaked.ca> - 2021-02-13 22:50 +0100
  Re: Missing memory and the mystery of MTRRs "Alexander V. Makartsev" <avbetev@gmail.com> - 2021-02-14 11:50 +0100
  Re: Missing memory and the mystery of MTRRs Georgi Naplatanov <gosho@oles.biz> - 2021-02-14 20:50 +0100
  Re: Missing memory and the mystery of MTRRs Charles Curley <charlescurley@charlescurley.com> - 2021-02-14 22:50 +0100
  Re: Missing memory and the mystery of MTRRs Henrique de Moraes Holschuh <hmh@debian.org> - 2021-02-16 17:10 +0100
    Re: Missing memory and the mystery of MTRRs Paul Duncan <paul.d@soi-team.org> - 2021-02-22 11:20 +0100

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