Resizable BAR and BAR1 64 GB
More actions
| Reported 8 GB and 10 GB | |
| Driver | cmpunlocker-patched driver |
|---|---|
| Unlock build | amoghmunikote/cmpunlocker (bar1-resize-unlock.patch, credit asm64-hooligan / JP) |
| Steps | Resizable BAR and BAR1 64 GB |
| Source | link |
| Confirmations | None yet. |
The stock card exposes BAR1 at 64 MiB. cmpunlocker can resize it to 64 GB, which is what large-BAR GPU-to-GPU P2P uses. It is in the README feature table as Working, credited to asm64-hooligan (JP). Whether it actually allocates depends on the motherboard.
How it works
bar1-resize-unlock.patch runs in nv_pci_probe for PCI IDs 0x20C2 and
0x2082: it maps the XVE registers at BAR0 + 0x88000, writes CYA +0x724 = 0x30
and CFG +0xDCC = 0x8000000A, then sets NVreg_EnableResizableBar = 1 so the driver attempts up
to 64 GB. (From the cmpunlocker patch source.) asm64's fork does the same as patch 0009.
The board must provide the space. You need Above 4G decoding and a large 64-bit MMIO window above 4 GB; a 64 GB BAR request fails on a board that only opens a 2-16 GB window.
Boards where BAR1 will not allocate
- ASUS WRX90 and Trust Inter's board: "BAR1, I can't arrange, no space"; no fix found, the agent ended up
suggesting an ASUS BIOS-mod ticket. Source: @trustinter, 2026-10-07
- Minisforum MS-01 (cards behind a PLX 88096): BAR1 stuck at 64 MB even with Resizable BAR enabled; MMIO is 256 GB
but the BIOS tries to place the BARs in a 512 MB section. The PLX 88096 firmware needs hotplug enabled to remap BAR addressing. Source: @replacedriver47, 2026-10-24 Same symptom reported on ASUS WRX80E and WRX90. Source: @replacedriver47, 2026-10-10
- ASUS P9X79 WS (X79): the BIOS allocates only a small window above 4 GB, so the 64 GB BAR fails; fixed from the OS
side by changing kernel parameters to enlarge the MMIOH window (exact params not captured; a longer write-up by
@fdelfini exists, see Discord). Source: @fdelfini, 2026-10-19
When the board cannot open the 64 GB BAR, use the mailbox P2P path instead, which runs inside the stock 64 MB BAR. Source: @ob88594, 2026-10-05
Known issue: VM compute hang
Warning In a Debian passthrough VM, after the unlock reported 64 GB and verify passed, any compute workload
hung the process and nvidia-smi stopped responding. The fix was to drop
bar1-resize-unlock.patch (remove the bar1_resize entry from
common/constants.yaml and the patch from the PATCH_ORDER array in
driver/build.sh), rebuild, and all 64 GB remained with no hangs. A longer write-up by @vipic exists; see
Discord. Source: @vipic, 2026-10-18
Verify
nvidia-smi -q | grep -A3 BAR1
lspci -s <bdf> -vvv | grep -i "Region 1"
Status
Works on boards that expose a large enough MMIO window; fails on several HEDT/PLX boards with no universal fix, so Reported, not Proven. Needs Above 4G decoding in BIOS.