bugGNU GRUB - Bugs: bug #61148, cutmem not wokring on old machines


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bug #61148: cutmem not wokring on old machines

Submitted by:  Alexey Kuznetsov <axet>
Submitted on:  Sun 12 Sep 2021 09:34:02 AM UTC  
Category:  None Severity:  Major
Priority:  5 - Normal Item Group:  None
Status:  None Privacy:  Public
Assigned to:  None Originator Name: 
Open/Closed:  Open Release: 
Release:  2.00 Reproducibility:  None
Planned Release:  None

Thu 16 Sep 2021 06:55:55 AM UTC, comment #3: 

My guess was limit memory map returned by e820 by size of 20M manually. So, I did patch grub source code with following:

diff --git a/grub-core/kern/i386/pc/mmap.old b/grub-core/kern/i386/pc/mmap.c
index c0c3c35..0eb76d9 100644
--- a/grub-core/kern/i386/pc/mmap.old
+++ b/grub-core/kern/i386/pc/mmap.c
@@ -134,6 +134,10 @@ grub_get_mmap_entry (struct grub_machine_mmap_entry *entry,
     entry->size = regs.ecx;

+  if (entry->addr == 0x0000000000100000) {
+    entry->len -= 0x1340000;
+  }
   /* return the continuation value */
   return regs.ebx;

But that did not succeed. Grub still works slowly. Does anyone know why kernel with 'mem=2020M' argument works fast, and same memory map does not fix grub 'slow down' issue?

Alexey Kuznetsov <axet>
Sun 12 Sep 2021 09:46:03 AM UTC, comment #2: 

I forget to mention 'grub-legacy' works fine, not slowdowns!

Alexey Kuznetsov <axet>
Sun 12 Sep 2021 09:40:57 AM UTC, comment #1: 
Alexey Kuznetsov <axet>
Sun 12 Sep 2021 09:34:02 AM UTC, original submission:  


My old notebook has memory issues and requires to cut memory region to work propertly.

From kernel perspective it looks like this:

[    0.000000] BIOS-provided physical RAM map:
[    0.000000] BIOS-e820: [mem 0x0000000000000000-0x000000000009fbff] usable
[    0.000000] BIOS-e820: [mem 0x000000000009fc00-0x000000000009ffff] reserved
[    0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff] reserved
[    0.000000] BIOS-e820: [mem 0x0000000000100000-0x000000007f73ffff] usable
[    0.000000] BIOS-e820: [mem 0x000000007f740000-0x000000007f74ffff] ACPI data
[    0.000000] BIOS-e820: [mem 0x000000007f750000-0x000000007f7fffff] ACPI NVS
[    0.000000] e820: remove [mem 0x7e400000-0xfffffffffffffffe] usable
[    0.000000] Notice: NX (Execute Disable) protection missing in CPU!
[    0.000000] user-defined physical RAM map:
[    0.000000] user: [mem 0x0000000000000000-0x000000000009fbff] usable
[    0.000000] user: [mem 0x000000000009fc00-0x000000000009ffff] reserved
[    0.000000] user: [mem 0x00000000000e0000-0x00000000000fffff] reserved
[    0.000000] user: [mem 0x0000000000100000-0x000000007e3fffff] usable
[    0.000000] user: [mem 0x000000007f740000-0x000000007f74ffff] ACPI data
[    0.000000] user: [mem 0x000000007f750000-0x000000007f7fffff] ACPI NVS

If this region is not removed my notebook works SUPER slow and every click takes few seconds to process. Same affects grub2. If region in use grub2 takes 2 minutes to boot into kernel. I recorded youtube video:


I know grub2 has a 'cutmem' command which is not working propertly. When I issue a:

'cutmem 0x7e40000 0x7f74ffff'

grub2 reports no changes is 'lsmmap' which is not correct. I tested 'cutmem' on my second notebook with efi loader, and cutmem affects 'lsmmap' output.

Here a few screenshots of grub2 boot process attached.

Alexey Kuznetsov <axet>


Attached Files
file #51901:  2021-09-13@11.41.13.jpg added by axet (1MiB - image/jpeg - corrent 'cutmem 0x7e400000 0x7f73ffff)
file #51896:  2021-09-12@12.20.38.jpg added by axet (1MiB - image/jpeg)


Depends on the following items: None found

Items that depend on this one: None found


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    Follow 2 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2021-09-13 axet Attached File- => Added 2021-09-13@11.41.13.jpg, #51901
    2021-09-12 axet Attached File- => Added 2021-09-12@12.20.38.jpg, #51896

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