[Offer] Mod Gigabyte GA-Z270-HD3P Rev. 1.0 BIOS F9d

BIOS/UEFI Modding Offers: Already modded special BIOSes
1

Hi,

I made a BIOS modification for the Gigabyte GA-Z270-HD3P Rev. 1.0, based on the official F9d BIOS.

The main purpose of this mod is to enable proper Above 4G MMIO allocation, which is useful for systems using GPUs with large BARs, such as the Tesla P100, and can also provide a useful starting point for further ReBAR / ReBarUEFI modifications.

Hardware tested

  • Gigabyte GA-Z270-HD3P Rev. 1.0

  • BIOS F9d modded

  • NVIDIA Tesla P100 16 GB

  • Debian 13

What has been modified

The relevant Setup IFR variables were identified and modified.

Aperture Size

VarStoreId: 0x0001
VarOffset: 0x070D
Original:   0x01  (256 MB)
Modified:   0x0F  (2048 MB)

Above 4GB MMIO BIOS assignment

VarStoreId: 0x0001
VarOffset: 0x07AF
Original:   0x00
Modified:   0x01

CSM Support

VarStoreId: 0x0001
VarOffset: 0x1486
Original:   0x01  (Enabled)
Modified:   0x00  (Disabled)

These values were present in three mirrored Setup NVAR copies, so all three were modified.

Result

The mod has been successfully tested on real hardware.

Linux now reports a large PCI MMIO window above 4 GB:

pci_bus 0000:00: root bus resource [mem 0x2000000000-0x2fffffffff window]

The Tesla P100 receives its 16 GB BAR above 4 GB:

Region 0: Memory at f6000000 [size=16M]
Region 1: Memory at 2800000000 [size=16G]
Region 3: Memory at 2c00000000 [size=32M]

The Intel HD Graphics 630 also receives 64-bit MMIO allocations above 4 GB.

Therefore, Above 4G / large MMIO allocation is confirmed working on this board with this mod.

Files

Modified BIOS – Q-Flash

GA-Z270-HD3P_F9d_Above4G_QFlash.patched

This version contain the Q-Flash validation bypass.

It was successfully flashed using Q-Flash, using the Fast option when asked.

Important

This is an experimental modified BIOS.

I have personally tested it on a GA-Z270-HD3P Rev. 1.0 and confirmed that the Above 4G/MMIO modification works, but I cannot guarantee compatibility with every hardware configuration.

Do not flash this on another motherboard model or revision.

If anyone wants to continue the work and implement ReBarUEFI / full ReBAR support, feel free to use this as a starting point.

Hopefully this is useful to other GA-Z270-HD3P owners. :slightly_smiling_face:


Edit by Fernando: Thread title shortened (details can be found within the initial post)

2

Hi!

I’ve tried using this bios on my Z270-HD3P.

First time it didn’t prompt me if I wanted fast or normal q flashing, so I proceded and got a black screen.

After forcefully powering off and booting up again bios was working, but I don’t know if it reverted itself to standard F9d.

I tried flashing again and this time I was able to choos fast mode and when it rebooted it showed the bios screen without trouble and was able to access the bios setup.

I don’t see any Above 4g decoding option in the bios menus, gpu-z on windows reports that bothabove 4g decoding and resize bar are disabled.

How can I know if I’m using your bios or if it autoreverted itself to the original one?

3

Hi!

I never had any issues with a black screen. Did you wait long enough? The first boot after flashing a new BIOS can take a while.

Indeed, this modded BIOS does not add a new option to the BIOS menu; it simply enables the feature in the background.

To be precise, the Above 4G Decoding code is already present in the original BIOS, but the corresponding option is not exposed in the UI. This mod simply forces it to be enabled.

This modded BIOS only enables Above 4G Decoding and does not include Resizable BAR support. Depending on the PCIe devices you are using, it may or may not be useful. This mod is particularly useful if you want to use a datacenter GPU, as in my case with the Tesla P100. However, it is probably of little use with a gaming GPU, since the system will not attempt to map the entire VRAM into the CPU’s address space without Resizable BAR enabled.

I believe enabling Resizable BAR might also be possible, but unfortunately, I haven’t been able to test it myself.

If you only need Above 4G Decoding and it doesn’t seem to be working with this mod, you may want to try disabling some legacy BIOS features, especially CSM support as it can cause trouble with this feature.

Finally, this mod does not display any specific information in the BIOS UI. I put it together fairly quickly, with the goal of enabling Above 4G Decoding while changing as little of the original BIOS as possible.