Not all RAM present

Fedora 42 kernel only exposes ~15 GB of system RAM out of 128 GB installed on Dell Precision 5860 Tower (Xeon w7-2475X, NVIDIA RTX 5000 Ada). 

Description

On a fresh install of Fedora 42 Workstation (GNOME), the system reports only ~14–16 GiB of available memory despite 128 GB ECC DDR5 RAM being installed and recognized by firmware diagnostics.

Dell BIOS diagnostics confirm all 128 GB is present and functional.
Nobara, RHEL, Ubuntu all have the same issue.

Steps to Reproduce

1. Install Fedora Linux 42 (Workstation Edition) on Dell Precision 5860 Tower

• CPU: Intel Xeon w7-2475X
• GPU: 2× NVIDIA RTX 5000 Ada
• RAM: 8 × 16 GB DDR5 ECC (128 GB total)

2. Boot into Fedora.
3. Check memory usage with free -h, inxi -m, or lsmem.

Actual Results

Only ~14.8 GiB of system RAM is available:

$ free -htotal        used        free      shared  buff/cache   availableMem:           14Gi       3.5Gi       6.2Gi       512Mi       4.6Gi        10Gi

$ inxi -mMemory:System RAM: total: 128 GiB available: 14.85 GiB used: 3.81 GiB (25.7%)Array-1: capacity: 4 TiB slots: 8 modules: 8Device-1–8: 16 GiB each (DDR5 ECC)

$ lsmemRANGE                                  SIZE  STATE REMOVABLE  BLOCK0x0000000000000000-0x0000000047ffffff  1.1G online       yes    0-80x0000000058000000-0x000000005fffffff  128M online       yes     110x0000000100000000-0x000000048fffffff 14.3G online       yes 32-145

So only ~15 GB is mapped online.

Expected Results

Fedora should detect and expose the full 128 GB of installed system RAM.

dmesg | grep -i memoryMemory:System RAM: total: 128 GiB available: 14.85 GiB used: 5.18 GiB (34.9%)Message: For most reliable report, use superuser + dmidecode.Array-1: capacity: 4 TiB note: check slots: 8 modules: 8EC: Single-bit ECCDevice-1: DIMM1 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-2: DIMM5 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-3: DIMM3 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-4: DIMM7 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-5: DIMM2 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-6: DIMM6 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-7: DIMM4 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/sDevice-8: DIMM8 type: DDR5 size: 16 GiB speed: spec: 5600 MT/sactual: 4400 MT/s

GPU Check

Not related to GPU VRAM:

glxinfo | grep -i 'Video memory'Video memory: 33016 MBDedicated video memory: 33016 MBCurrently available dedicated video memory: 33011 MB

Additional Information

• BIOS diagnostics: All 128 GB detected and passed memory test.
  Bios installed is:

  # sudo dmidecode -t bios | grep -i version
  Version: 3.0.2

• Other operating systems tested (Nobara, RHEL, Ubuntu, Fedora) fail to see.
• Some documentation suggests setting a manual memory limit in GRUB, but this does not work either

Environment

• OS: Fedora 42 Workstation (GNOME 48.4)
• Kernel: 6.15.9-201.fc42.x86_64
• CPU: Intel Xeon w7-2475X (40 cores @ 4.80 GHz)
• Memory: 8 × 16 GB DDR5 ECC (128 GB total)
• GPU: 2 × NVIDIA RTX 5000 Ada Generation
• Host: Dell Precision 5860 Tower

Worked with Fedora and RHEL and they seem to believe it is tied to UEFI Reserving memory or interaction between BIOS and Linux.

Has anyone seen this?