On Fri, Jun 24, 2022 at 11:47 AM Dave Hansen [off-list ref] wrote:

On 6/24/22 10:19, Marc Orr wrote:

quoted

quoted

Is this a matter of

        can boot from a guest firmware that doesn't pre-validate all the
        guest memory?

or

        can boot from a guest firmware that doesn't pre-validate all the
        guest memory ... with access to all of that guest's RAM?

In other words, are we talking about "fails to boot" or "can't see all
the RAM"?

Ah... yeah, you're right, Dave -- I guess it's the latter. The guest
won't have access to all of the memory that the customer is paying
for. But that's still bad. If the customer buys a 96 GB VM and can
only see 4GB because they're kernel doesn't have these patches they're
going to be confused and frustrated.

They'll at least be a _bit_ less angry and frustrated than if they were
staring at a blank screen. ;)  But, yeah, I totally get the point.

Ha! Well we do have that issue in some cases. If you try to run an SEV
VM with an image that doesn't support SEV you will just get a blank
serial screen. If we had something like this back then the FW could
have surfaced a nice error to the user but that's history now.

How big is the window going to be where we have guests that can have
unaccepted memory, but don't have acceptance support?  For TDX, it's
looking like it'll probably _just_ be 5.19.  Is TDX on 5.19 in shape
that cloud providers can deploy it?  Or, is stuff like lack of
attestation a deal breaker?

This is complicated because distros don't run upstream linux versions.
If I understand correctly (I see some distro emails on here so please
correct me) distros normally maintain forks which they backport things
into. So I cannot answer this question. It is possible that a
hypothetical distro backports only the SNP/TDX initial patches and
doesn't take these for many releases.

I am more familiar with SNP and it does have some attestation support
in the first patch sets.

Also I should have been more clear. I don't want to try and hold up
this feature but instead discuss a future usability add-on feature.