> On Feb 6, 2023, at 10:25 AM, ritul guru <ritul.bits@gmail.com> wrote:
> 
> Thanks,
> so as it is memory, does it mean if anything written in variable store, and VM reboot happens then variable store will be flushed?
> 

It looks like it is saved if you do an S3. S3 is ACPI speak for a sleep state that puts RAM into self refresh. On a cold boot it allocates the memory, so you are starting over.

Sorry I’ve never looked at the Xen code before so I’m sight reading.

Thanks,

Andrew Fish

> Thanks & Regards
> Ritul Guru
> +91-9916513186
> 
> 
> On Mon, Feb 6, 2023 at 11:47 PM Andrew (EFI) Fish <afish@apple.com <mailto:afish@apple.com>> wrote:
>> 
>> 
>>> On Feb 6, 2023, at 8:06 AM, ritul guru <ritul.bits@gmail.com <mailto: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:
>> 
>> <edk2.png>
>> edk2/OvmfXen.fdf at master · tianocore/edk2
>> github.com
>>  <https://github.com/tianocore/edk2/blob/master/OvmfPkg/OvmfXen.fdf>edk2/OvmfXen.fdf at master · tianocore/edk2 <https://github.com/tianocore/edk2/blob/master/OvmfPkg/OvmfXen.fdf>
>> github.com <https://github.com/tianocore/edk2/blob/master/OvmfPkg/OvmfXen.fdf>
>> 
>> Oh looks like it uses an emulated variable store that is just memory. See ReserveEmuVariableNvStore().
>> 
>> 
>> edk2/Platform.c at master · tianocore/edk2
>> github.com
>>  <https://github.com/tianocore/edk2/blob/master/OvmfPkg/XenPlatformPei/Platform.c#L365>edk2/Platform.c at master · tianocore/edk2 <https://github.com/tianocore/edk2/blob/master/OvmfPkg/XenPlatformPei/Platform.c#L365>
>> github.com <https://github.com/tianocore/edk2/blob/master/OvmfPkg/XenPlatformPei/Platform.c#L365>
>> 
>> Thanks,
>> 
>> Andrew Fish
>> 
>>> 
>>> https://wiki.osdev.org/Using_UEFI_Runtime_Services_in_your_Kernel
>>> 
>>> Thanks & Regards
>>> Ritul Guru
>>> +91-9916513186
>>> 
>> 
> <edk2.png>