Hello,

On Tue, Jan 26, 2021 at 12:49:14PM -0800, David Rientjes wrote:

quoted

SEV-SNP, another incremental enhancement (on SEV-ES), further strengthens the
argument for SEV and SEV-* coexistenence.  SEV-SNP and SEV-ES will share the
same ASID range, so the question is really, "do we expect to run SEV guests and
any flavor of SEV-* guests on the same platform".  And due to SEV-* not being
directly backward compatible with SEV, the answer will eventually be "yes", as
we'll want to keep running existing SEV guest while also spinning up new SEV-*
guests.

Agreed, cloud providers will most certainly want to run both SEV and SEV-* 
guests on the same platform.

Am I correct in thinking that the reason why these IDs are limited is
because they need to be embedded into the page table entries? If so, we
aren't talking about that many IDs and having to divide the already small
pool into disjoint purposes doesn't seem like a particularly smart use of
those bits. It is what it is, I guess.

I'm slightly concerned about extensibility if there is to be an 
incremental enhancement atop SEV-* or TDX with yet another pool of 
encryption ids.  (For example, when we only had hugepages, this name was 
perfect; then we got 1GB pages which became "gigantic pages", so are 512GB 
pages "enormous"? :)  I could argue (encryption_ids.basic.*,
encryption_ids.enhanced.*) should map to 
(encryption_ids.legacy.*, encryption_ids.*) but that's likely 
bikeshedding.

Thomas: does encryption_ids.{basic,enhanced}.* make sense for ASID 
partitioning?

Tejun: if this makes sense for legacy SEV and SEV-* per Thomas, and this 
is now abstracted to be technology (vendor) neutral, does this make sense 
to you?

The whole thing seems pretty immature to me and I agree with you that coming
up with an abstraction at this stage feels risky.

I'm leaning towards creating a misc controller to shove these things into:

* misc.max and misc.current: nested keyed files listing max and current
  usage for the cgroup.

* Have an API to activate or update a given resource with total resource
  count. I'd much prefer the resource list to be in the controller itself
  rather than being through some dynamic API just so that there is some
  review in what keys get added.

* Top level cgroup lists which resource is active and how many are
  available.

So, behavior-wise, not that different from the proposed code. Just made
generic into a misc controller. Would that work?

Thanks.

-- 
tejun