Re: New "IndustryStandard" fw_cfg?

[Gerd Hoffmann]

On Thu, Jun 16, 2022 at 01:49:11PM +0800, Xiaoyao Li wrote:
> On 6/16/2022 1:37 PM, Gerd Hoffmann wrote:
> >    Hi,
> > 
> > > Per my understanding, Unaccepted Memory in UEFI is introduced for
> > > confidential VMs, i.e., for Intel TDX and AMD SEV-SNP. The only reason
> > > UEFI/OVMF reports "Unaccepted Memory" to OS, is a confidential VM is
> > > desired.
> > 
> > No.  Reporting "Unaccepted Memory" to the OS is not a hard requirement
> > for confidential VMs, it only optimizes boot times.  Instead of doing
> > that time-consuming process in the firmware for all memory we tell the
> > guest OS which memory is accepted already and which is not.  So the
> > guest OS can go accept the remaining memory in a background process.
> 
> But for non-confidential VMs, even a range of memory is reported as
> unaccepted nothing prevents it from being accessed without accepting it, and
> it's not time-consuming. Did I miss anything?

The concept of "Unaccepted Memory" only exists for confidential VM.

That doesn't imply the guest OS must be able to handle unaccepted
memory though because it is possible to simply accept all memory
in the firmware.  Which in fact is the common case today.

take care,
  Gerd