[edk2-devel] regarding calling UEFI runtime services (mainly SetVariable) from linux or android OS which is running on xen+tianocore UEFI

[ritul guru]

ohh, it should retains value on VM reboot.

//
// Allocate storage for NV variables early on so it will be
// at a consistent address. Since VM memory is preserved
// across reboots, this allows the NV variable storage to survive
// a VM reboot.
//



*Thanks & RegardsRitul Guru+91-9916513186*


On Mon, Feb 6, 2023 at 11:55 PM ritul guru <ritul.bits at 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?
>
>
>
> *Thanks & RegardsRitul Guru+91-9916513186*
>
>
> On Mon, Feb 6, 2023 at 11:47 PM Andrew (EFI) Fish <afish at apple.com> wrote:
>
>>
>>
>> On Feb 6, 2023, at 8:06 AM, ritul guru <ritul.bits at 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:
>>
>> [image: edk2.png]
>>
>> 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>
>> <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().
>>
>> [image: edk2.png]
>>
>> 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>
>>
>> <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 & RegardsRitul Guru+91-9916513186*
>> 
>>
>>
>>


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