User:0xdc/Drafts/Configure Intel GPU Aperture Size via hidden UEFI settings

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This guide is for Intel GPU users who want to use GVT-g to virtualise their GPU in VMs, but need to increase the GPU's aperture size to support more virtual graphics cards and/or larger resolutions.

Check CPU/chipset support

First, check that your computer is compatible. It must support hardware virtualisation (in this guide, specifically KVM) and Vt-d/VFIO. Most importantly, your CPU must be supported in the driver.

Check current settings

root #lspci -v -s 00.02.0

Memory at 4000000000 (64-bit, prefetchable) [size=256M]


Download your BIOS

From your computer manufacturer's website, download a copy of the BIOS update package.

some examples
Computer name BIOS download list Direct Download Note
ASRock B460M Pro4 GVT with Comet Lake-S CPUs
Lenovo X1 Carbon Gen 8 Requires app-arch/cabextract
ASRock Z87E-ITX Does not support kvmgt with Haswell (should support xengt), Broadwell should support both kvmgt/xengt
ASRock Rack C2750D4I Not an Intel GPU (ast_drv), does not support GVT-g
Dell XPS 13 7390 2-in-1 Ice Lake does not support GVT, extraction


qmake and other Qt libraries may be required.

user $(cd UEFITool; qmake && make -j$(nproc))
user $./UEFITool/UEFITool &

Extract your BIOS update file until you get a readable binary file that UEFITool can use. Once opened, open the Find window and search for the text "Aperture Size". Double click the first match from the log at the bottom of the window. Right-click the highlighted section and "Extract as-is".


user $cmake -B Universal-IFR-Extractor/build -G Ninja Universal-IFR-Extractor
user $ninja -C Universal-IFR-Extractor/build
user $cp Universal-IFR-Extractor/build/ifrextract .

With the extracted image section, pass the filename to ifrextract:

user $./ifrextract section.bin setup.txt

Determine hidden section locations

In the setup.txt file, search for the "Aperture Size" option.

user $sed '/One Of: Aperture Size/,/End One/!d' setup.txt
0x79534 		One Of: Aperture Size, VarStoreInfo (VarOffset/VarName): 0x44, VarStore: 0x2, QuestionId: 0x2A0, Size: 1, Min: 0x0, Max 0xF, Step: 0x0 {05 91 72 13 73 13 A0 02 02 00 44 00 10 10 00 0F 00}
0x79545 			Default: DefaultId: 0x0, Value (Other) {5B 85 00 00 08}
0x7954A 				Value {5A 82}
0x7954C 					64 Bit Unsigned Int: 0x1 {45 0A 01 00 00 00 00 00 00 00}
0x79556 				End {29 02}
0x79558 			End {29 02}
0x7955A 			One Of Option: 128MB, Value (8 bit): 0x0 {09 07 74 13 00 00 00}
0x79561 			One Of Option: 256MB, Value (8 bit): 0x1 {09 07 75 13 00 00 01}
0x79568 			One Of Option: 512MB, Value (8 bit): 0x3 {09 07 76 13 00 00 03}
0x7956F 			One Of Option: 1024MB, Value (8 bit): 0x7 {09 07 77 13 00 00 07}
0x79576 			One Of Option: 2048MB, Value (8 bit): 0xF {09 07 78 13 00 00 0F}
0x7957D 		End One Of {29 02}

In this example, the offset is 0x44, the VarStoreId is 0x2 and the aperture size values can be one of 0x0, 0x1, 0x3, 0x7, and 0xF.

To find out the name of the VarStore:

user $grep -a 'VarStoreId: 0x2' setup.txt
0x711A9 	VarStoreEFI: VarStoreId: 0x2 [72C5E28C-7783-43A1-8767-FAD73FCCAFA4], Attrubutes: 7, Size: 28F, Name: SaSetup {26 22 02 00 8C E2 C5 72 83 77 A1 43 87 67 FA D7 3F CC AF A4 07 00 00 00 8F 02 53 61 53 65 74 75 70 00}

In this case, VarStoreId: 0x2 has the name SaSetup.

Set UEFI hidden variable with modGRUBshell

Download or compile the modified GRUB UEFI shell that has the ability to edit hidden settings, and add it to your UEFI bootloader (e.g. efibootmgr).

root #efibootmgr -L modGRUBshell -d /dev/... -p 1 -l '\modGRUBshell.efi'

Reboot into the shell.

In the shell, run the command, replacing your values:

setup_var_cv SaSetup 0x44 0x1 0xF
name of VarStore offset size value
root ## Check current setting
root #setup_var_cv SaSetup 0x44 0x1
root ## Set new value
root #setup_var_cv SaSetup 0x44 0x1 0xF
root ## Verify that the value has changed
root #setup_var_cv SaSetup 0x44 0x1

Reboot, then re-verify the aperture size from the OS.

See Also