Re: [RFC Patch 0/2] KVM: SVM: Cgroup support for SVM SEV ASIDs

[Vipin Sharma]

On Tue, Nov 24, 2020 at 07:16:29PM +0000, Sean Christopherson wrote:
> On Fri, Nov 13, 2020, David Rientjes wrote:                                     
> >                                                                               
> > On Mon, 2 Nov 2020, Sean Christopherson wrote:                                
> >                                                                               
> > > On Fri, Oct 02, 2020 at 01:48:10PM -0700, Vipin Sharma wrote:               
> > > > On Fri, Sep 25, 2020 at 03:22:20PM -0700, Vipin Sharma wrote:             
> > > > > I agree with you that the abstract name is better than the concrete     
> > > > > name, I also feel that we must provide HW extensions. Here is one       
> > > > > approach:                                                               
> > > > >                                                                         
> > > > > Cgroup name: cpu_encryption, encryption_slots, or memcrypt (open to     
> > > > > suggestions)                                                            
> > > > >                                                                         
> > > > > Control files: slots.{max, current, events}                             
> > >                                                                             
> > > I don't particularly like the "slots" name, mostly because it could be confused
> > > with KVM's memslots.  Maybe encryption_ids.ids.{max, current, events}?  I don't
> > > love those names either, but "encryption" and "IDs" are the two obvious     
> > > commonalities betwee TDX's encryption key IDs and SEV's encryption address  
> > > space IDs.                                                                  
> > >                                                                             
> >                                                                               
> > Looping Janosch and Christian back into the thread.                           
> >                                                                               
> > I interpret this suggestion as                                                
> > encryption.{sev,sev_es,keyids}.{max,current,events} for AMD and Intel         
> 
> I think it makes sense to use encryption_ids instead of simply encryption, that
> way it's clear the cgroup is accounting ids as opposed to restricting what
> techs can be used on yes/no basis.
> 
> > offerings, which was my thought on this as well.                              
> >                                                                               
> > Certainly the kernel could provide a single interface for all of these and    
> > key value pairs depending on the underlying encryption technology but it      
> > seems to only introduce additional complexity in the kernel in string         
> > parsing that can otherwise be avoided.  I think we all agree that a single    
> > interface for all encryption keys or one-value-per-file could be done in      
> > the kernel and handled by any userspace agent that is configuring these       
> > values.                                                                       
> >                                                                               
> > I think Vipin is adding a root level file that describes how many keys we     
> > have available on the platform for each technology.  So I think this comes    
> > down to, for example, a single encryption.max file vs                         
> > encryption.{sev,sev_es,keyid}.max.  SEV and SEV-ES ASIDs are provisioned      
> 
> Are you suggesting that the cgroup omit "current" and "events"?  I agree there's
> no need to enumerate platform total, but not knowing how many of the allowed IDs
> have been allocated seems problematic.
> 

We will be showing encryption_ids.{sev,sev_es}.{max,current}
I am inclined to not provide "events" as I am not using it, let me know
if this file is required, I can provide it then.

I will provide an encryption_ids.{sev,sev_es}.stat file, which shows
total available ids on the platform. This one will be useful for
scheduling jobs in the cloud infrastructure based on total supported
capacity.

> > separately so we treat them as their own resource here.                       
> >                                                                               
> > So which is easier?                                                           
> >                                                                               
> > $ cat encryption.sev.max                                                      
> > 10                                                                            
> > $ echo -n 15 > encryption.sev.max                                             
> >                                                                               
> > or                                                                            
> >                                                                               
> > $ cat encryption.max                                                          
> > sev 10                                                                        
> > sev_es 10                                                                     
> > keyid 0                                                                       
> > $ echo -n "sev 10" > encryption.max                                           
> >                                                                               
> > I would argue the former is simplest (always preferring                       
> > one-value-per-file) and avoids any string parsing or resource controller      
> > lookups that need to match on that string in the kernel.                      
> 
> Ya, I prefer individual files as well.
> 
> I don't think "keyid" is the best name for TDX, it doesn't leave any wiggle room
> if there are other flavors of key IDs on Intel platform, e.g. private vs. shared
> in the future.  It's also inconsistent with the SEV names, e.g. "asid" isn't
> mentioned anywhere.  And "keyid" sort of reads as "max key id", rather than "max
> number of keyids".  Maybe "tdx_private", or simply "tdx"?  Doesn't have to be
> solved now though, there's plenty of time before TDX will be upstream. :-)
> 
> > The set of encryption.{sev,sev_es,keyid} files that exist would depend on     
> > CONFIG_CGROUP_ENCRYPTION and whether CONFIG_AMD_MEM_ENCRYPT or                
> > CONFIG_INTEL_TDX is configured.  Both can be configured so we have all        
> > three files, but the root file will obviously indicate 0 keys available       
> > for one of them (can't run on AMD and Intel at the same time :).              
> >                                                                               
> > So I'm inclined to suggest that the one-value-per-file format is the ideal    
> > way to go unless there are objections to it.