> On Feb 6, 2023, at 8:06 AM, ritul guru <ritul.bits@gmail.com> wrote:
> 
> Hi,
> 
> I have been using xen hypervisor and tianocore uefi BIOS on xen to boot to ubuntu OS on virtualized disk.
> and want to set a UEFI variable with UEFI runtime service SetVariable() to a value and the same wants to read from UEFI bootloader either grubx64.efi or botmgfw.efi,
> So, Is it possible to use runtime services to do such an operation for OS running on VM when booted with OVMF/tianocore BIOS on VM guest? 
> If so, where does this variable gets stored? is it in some virtualized disk as there is no virtualized SPIROM available to VM.
> 
> 

I don’t know the Xen specifics, but the firmware maps in a Flash Device (FD) here:

https://github.com/tianocore/edk2/blob/master/OvmfPkg/OvmfXen.fdf
edk2/OvmfXen.fdf at master · tianocore/edk2
github.com

Oh looks like it uses an emulated variable store that is just memory. See ReserveEmuVariableNvStore().

https://github.com/tianocore/edk2/blob/master/OvmfPkg/XenPlatformPei/Platform.c#L365
edk2/Platform.c at master · tianocore/edk2
github.com

Thanks,

Andrew Fish

> 
> https://wiki.osdev.org/Using_UEFI_Runtime_Services_in_your_Kernel
> 
> Thanks & Regards
> Ritul Guru
> +91-9916513186
>