linux-kernel - Re: [Patch v3 0/2] cgroup: KVM: New Encryption IDs cgroup controller

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Date:   Thu, 10 Dec 2020 15:54:01 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Tejun Heo <tj@...nel.org>, Vipin Sharma <vipinsh@...gle.com>
Cc:     thomas.lendacky@....com, brijesh.singh@....com, jon.grimm@....com,
        eric.vantassell@....com, pbonzini@...hat.com, seanjc@...gle.com,
        lizefan@...wei.com, hannes@...xchg.org, frankja@...ux.ibm.com,
        corbet@....net, joro@...tes.org, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, hpa@...or.com, gingell@...gle.com,
        rientjes@...gle.com, dionnaglaze@...gle.com, kvm@...r.kernel.org,
        x86@...nel.org, cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v3 0/2] cgroup: KVM: New Encryption IDs cgroup controller

On 09.12.20 21:58, Tejun Heo wrote:
> Hello,
> 
> Rough take after skimming:
> 
> * I don't have an overall objection. In terms of behavior, the only thing
>   which stood out was input rejection depending on the current usage. The
>   preferred way of handling that is rejecting future allocations rather than
>   failing configuration as that makes it impossible e.g. to lower limit and
>   drain existing usages from outside the container.
> 
> * However, the boilerplate to usefulness ratio doesn't look too good and I
>   wonder whether what we should do is adding a generic "misc" controller
>   which can host this sort of static hierarchical counting. I'll think more
>   on it.

We first dicussed to have
encryption_ids.stat
encryption_ids.max
encryption_ids.current

and we added the sev in later, so that we can also have tdx, seid, sgx or whatever.
Maybe also 2 or more things at the same time.

Right now this code has

encryption_ids.sev.stat
encryption_ids.sev.max
encryption_ids.sev.current

And it would be trivial to extend it to have
encryption_ids.seid.stat
encryption_ids.seid.max
encryption_ids.seid.current
on s390 instead (for our secure guests).

So in the end this is almost already a misc controller, the only thing that we
need to change is the capability to also define things other than encryption.*.*
And of course we would need to avoid adding lots of random garbage to such a thing.

But if you feel ok with the burden to keep things kind of organized a misc
controller would certainly work for the encryption ID usecase as well. 
So I would be fine with the thing as is or a misc controlĺer.

Christian