Re: [RFC PATCH v3 17/36] pflash_cfi01/tdx: Introduce ram_mode of pflash for TDVF

[Daniel P . Berrangé]

On Thu, Mar 24, 2022 at 02:13:53PM +0800, Xiaoyao Li wrote:
> On 3/22/2022 5:29 PM, Daniel P. Berrangé wrote:
> > On Tue, Mar 22, 2022 at 10:21:41AM +0100, Gerd Hoffmann wrote:
> > >    Hi,
> > > 
> > > > > If you don't need a pflash device, don't use it: simply map your nvram
> > > > > region as ram in your machine. No need to clutter the pflash model 
> > > > > like
> > > > > that.
> > > 
> > > Using the pflash device for something which isn't actually flash looks a
> > > bit silly indeed.
> > > 
> > > > 
> > > > I know it's dirty to hack the pflash device. The purpose is to make the 
> > > > user
> > > > interface unchanged that people can still use
> > > > 
> > > >         -drive if=pflash,format=raw,unit=0,file=/path/to/OVMF_CODE.fd
> > > >          -drive if=pflash,format=raw,unit=1,file=/path/to/OVMF_VARS.fd
> > > > 
> > > > to create TD guest.
> > > 
> > > Well, if persistent vars are not supported anyway there is little reason
> > > to split the firmware into CODE and VARS files.  You can use just use
> > > OVMF.fd with a single pflash device.  libvirt recently got support for
> > > that.
> > 
> > Agreed.
> 
> The purpose of using split firmware is that people can share the same
> code.fd while using different vars.fd

That's fine for firmware that writes to vars.fd, but it was said earlier
that changes aren't written with TDX (nor are they written with SEV),
so a separate vars.fd serves no pupose in these cases.

With regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|