[Qemu-devel] OVMF NvVars in flash, on KVM [was: OvmfPkg/NvVarsFileLib: handle the inital file not found]

[Laszlo Ersek <lersek@redhat.com>]

I'm derailing this preexistent edk2-devel thread for public benefit :)

On 06/24/13 23:36, Jordan Justen wrote:
> On Mon, Jun 24, 2013 at 2:18 PM, Laszlo Ersek <lersek@redhat.com>
> wrote:
>> On 06/24/13 23:06, Jordan Justen wrote:
>>> We could consider yanking all these hacks out, and just forcing
>>> people to use QEMU with flash support when that eventually gets
>>> finished.
>>>
>>> But, some people like the idea that the 'disk image' can decide the
>>> boot order, so I'm not sure what the eventual solution will be.
>>
>> I think we should keep (improving) the on-disk NvVars stuff until the
>> flash support is complete.
>>
>> BTW could you please summarize the status on that? I believe KVM and
>> qemu already have the necessary commits (could you identify them
>> perhaps?)
>
> Yes, it is currently supported on QEMU master. For non-KVM, it
> should work since QEMU 1.2. For KVM, it should work as of the
> next QEMU release (1.6) whenever that happens.
>
> But, recently someone noted a regression with this support, so
> I need to investigate this.
>
>> and that you have a WIP series for OVMF -- what needs to be
>> done there?
>
> 2 things I know of:
> * Clean up or perhaps just push fwd my ovmf-nvvars branch
>   https://github.com/jljusten/edk2/tree/ovmf-nvvars
> * Push fwd a fix for a boot issue with X64 page tables residing
>   in the 'ROM/flash' memory with the newer KVM read-only
>   memory support. (The same support that makes flash possible
>   on KVM causes OVMF to not boot for me.) I have a fix for
>   this.

>From a more recent discussion,

On 07/10/13 15:19, Gleb Natapov wrote:
> On Wed, Jul 10, 2013 at 02:45:21PM +0200, Laszlo Ersek wrote:
>> I'm still very confused about the interplay between emulated flash
>> and KVM. If anyone can post a summary, I'd be grateful.
>>
> If you want to run code from emulated flash you need RO memory support
> in KVM. It is possible to implement flash without RO memory, but you
> will not be able to put UEFI code into it. I do not know where
> requirement that UEFI and non-volatile variables should be on the same
> flash is coming from. Can we put UEFI into a ROM and provide separate
> flash to store non-volatile variables?

I have no idea what to answer, but I desperately want this to work :)
Currently I can't spend much time on it (and of course I'm not prodding
anyone to do it for me), I'd just like to understand the status.

So, what *exact* upstream Linux commit adds RO memory support to KVM (on
x86_64)?

How would a single *hardware* flash device store both (compressed) UEFI
code and (rewriteable) non-volatile variables?

What else do flash + KVM depend on? Can you guys please talk to each
other directly and let me just listen in? :)

Thanks!
Laszlo