View source for Resizable BAR and BAR1 64 GB

{{Unlock
|unlocks=Resizable BAR / BAR1 64 GB
|variant=both
|driver_version=cmpunlocker-patched driver
|unlock_build=amoghmunikote/cmpunlocker (bar1-resize-unlock.patch, credit asm64-hooligan / JP)
|steps_page=Resizable BAR and BAR1 64 GB
|status=Reported
|tested_by=asm64-hooligan
|source=https://github.com/amoghmunikote/cmpunlocker
}}

The stock card exposes BAR1 at '''64 MiB'''. [[Driver unlock|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 ==

<code>bar1-resize-unlock.patch</code> runs in <code>nv_pci_probe</code> for PCI IDs <code>0x20C2</code> and
<code>0x2082</code>: it maps the XVE registers at BAR0 + <code>0x88000</code>, writes CYA <code>+0x724 = 0x30</code>
and CFG <code>+0xDCC = 0x8000000A</code>, then sets <code>NVreg_EnableResizableBar = 1</code> 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|https://discord.com/channels/1518634379604136178/1518692084729511967/1557375372662673490}}
* '''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|https://discord.com/channels/1518634379604136178/1534370835220004885/1563580726882861097}}
  Same symptom reported on '''ASUS WRX80E''' and WRX90. {{Source|replacedriver47|2026-10-10|https://discord.com/channels/1518634379604136178/1518695289278566450/1558565136980254791}}
* '''ASUS P9X79 WS''' (X79): the BIOS allocates only a small window above 4 GB (its agent put it at 2-16 GB), so the
  64 GB BAR fails. fdelfini's board already had Above 4G decoding; his agent changed Ubuntu kernel parameters to enlarge
  the MMIOH window and it then worked. The exact parameters were not posted, so this is an OS-side MMIOH-window fix to
  reproduce, not a recipe yet. {{Source|fdelfini|2026-10-19|https://discord.com/channels/1518634379604136178/1518692084729511967/1561810276351741975}}

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|https://discord.com/channels/1518634379604136178/1518692084729511967/1556527198540922981}}

== Known issue: VM compute hang ==

{{Status|warning}} In a Debian passthrough VM, after the unlock reported 64 GB and verify passed, any compute workload
hung the process and <code>nvidia-smi</code> stopped responding. The fix was to '''drop
<code>bar1-resize-unlock.patch</code>''' (remove the <code>bar1_resize</code> entry from
<code>common/constants.yaml</code> and the patch from the <code>PATCH_ORDER</code> array in
<code>driver/build.sh</code>), rebuild, and all 64 GB remained with no hangs. That patch writes the XVE BAR1 registers for
PCI IDs <code>0x20C2</code> and <code>0x2082</code> and enables <code>NVreg_EnableResizableBar</code>; without it there
are no hangs and the card keeps 64 GB. The hang appeared only after a bootloader repair, kernel update and cmpunlocker
reinstall; ViPiC suspected the hypervisor not fully resetting the card between VM reboots.
{{Source|vipic|2026-10-18|https://discord.com/channels/1518634379604136178/1518692084729511967/1561429038361223329}}

== Verify ==

<syntaxhighlight lang="bash">
nvidia-smi -q | grep -A3 BAR1
lspci -s <bdf> -vvv | grep -i "Region 1"
</syntaxhighlight>

== Status ==

Works on boards that expose a large enough MMIO window; fails on several HEDT/PLX boards with no universal fix, so
{{Status|Reported}}, not Proven. Needs Above 4G decoding in BIOS.

== Related ==

[[P2P]], [[Platforms]], [[Driver unlock]], [[Kernel parameters and module options]], [[Troubleshooting]].

{{ImportFooter}}
[[Category:Unlocks]]
[[Category:8 GB]]
[[Category:10 GB]]