On Thu, Jun 04, 2020 at 01:39:22AM -0300, Thiago Jung Bauermann wrote:
> 
> Hello David,
> 
> David Gibson <david@gibson.dropbear.id.au> writes:
> 
> > A number of hardware platforms are implementing mechanisms whereby the
> > hypervisor does not have unfettered access to guest memory, in order
> > to mitigate the security impact of a compromised hypervisor.
> >
> > AMD's SEV implements this with in-cpu memory encryption, and Intel has
> > its own memory encryption mechanism.  POWER has an upcoming mechanism
> > to accomplish this in a different way, using a new memory protection
> > level plus a small trusted ultravisor.  s390 also has a protected
> > execution environment.
> >
> > The current code (committed or draft) for these features has each
> > platform's version configured entirely differently.  That doesn't seem
> > ideal for users, or particularly for management layers.
> >
> > AMD SEV introduces a notionally generic machine option
> > "machine-encryption", but it doesn't actually cover any cases other
> > than SEV.
> >
> > This series is a proposal to at least partially unify configuration
> > for these mechanisms, by renaming and generalizing AMD's
> > "memory-encryption" property.  It is replaced by a
> > "guest-memory-protection" property pointing to a platform specific
> > object which configures and manages the specific details.
> >
> > For now this series covers just AMD SEV and POWER PEF.  I'm hoping it
> 
> Thank you very much for this series! Using a machine property is a nice
> way of configuring this.
> 
> >From an end-user perspective, `-M pseries,guest-memory-protection` in
> the command line already expresses everything that QEMU needs to know,
> so having to add `-object pef-guest,id=pef0` seems a bit redundant. Is
> it possible to make QEMU create the pef-guest object behind the scenes
> when the guest-memory-protection property is specified?

Not exactly - the object needs to exist for the QOM core to resolve it
before we'd have a chance to look at the value to conditionally create
the object.

What we could do, however, is always create a PEF object in the
machine, and it would just have no effect if the machine parameter
wasn't specified.

I did consider that option, but left it this way for greater
consistency with AMD SEV - there the object can't be auto-created,
since it has mandatory parameters needed to configure the encryption.

I'm open to persuasion about changing that, though.

> Regardless, I was able to successfuly launch POWER PEF guests using
> these patches:
> 
> Tested-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>

Ah, great.

> > can be extended to cover the Intel and s390 mechanisms as well,
> > though.
> >
> > Note: I'm using the term "guest memory protection" throughout to refer
> > to mechanisms like this.  I don't particular like the term, it's both
> > long and not really precise.  If someone can think of a succinct way
> > of saying "a means of protecting guest memory from a possibly
> > compromised hypervisor", I'd be grateful for the suggestion.
> 
> Is "opaque guest memory" any better? It's slightly shorter, and slightly
> more precise about what the main characteristic this guest property conveys.
> 

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson