[edk2-devel] OVMF: NV Variable Store Layout of Larger Build Targets

[Gerd Hoffmann]

  Hi,

> The current maximum image size of an OVMF image is 4MB, which is
> insufficient for storing even a minimal and compressed kernel and initramfs.
> To get around this, we've been maintaining our own fork of EDK2 that adds
> 8MiB and 16MiB OVMF build targets that have enough room in the DXE volume to
> store a reasonably-sized kernel and initramfs. However, it would be
> convenient if upstream EDK2 supported these larger OVMF targets.

I'm wondering whenever it makes sense to have the 8M option.  I think
I'd tend to go straight to 16M (which is the max size we can do on x86).

> However, as Laszlo mentioned, introducing a larger volume size is
> compatibility breaking, and so seizing the opportunity to come up
> with a larger non-volatile variable store layout is necessary.
> 
> That said, I would like to use this thread to discuss among hardware
> vendors an optimal variable store layout for these larger image sizes.

The 2M -> 4M switch happened because the varstore was too small.  It was
Confirm64KilobytesOfUnauthenticatedVariableStorage test of the the
Microsoft Hardware Certification failing.  I guess Microsoft has good
reasons to test for 64k varstore, probably they expect this is big
enough in practice.

The varstore size of the 4M layout is *way* above that (see 2M -> 4M
commit message):

  Variable store      56 ->   256 ( +200)
  Spare area          64 ->   264 ( +200)

Assuming 256k varstore is more than enough:  Sticking to the 4M variable
store layout for the 16M (and maybe 8M) builds looks like the best
option to me.  I think the varstore would be identical for 4M and 16M
builds then, so it should be possible to switch guests from 4M to 16M
while keeping the varstore.

take care,
  Gerd



-=-=-=-=-=-=-=-=-=-=-=-
Groups.io Links: You receive all messages sent to this group.
View/Reply Online (#79942): https://edk2.groups.io/g/devel/message/79942
Mute This Topic: https://groups.io/mt/85034796/1813853
Group Owner: devel+owner at edk2.groups.io
Unsubscribe: https://edk2.groups.io/g/devel/unsub [edk2-devel-archive at redhat.com]
-=-=-=-=-=-=-=-=-=-=-=-