linux-kernel - Re: [Patch v4 1/2] cgroup: svm: Add Encryption ID controller

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Message-ID: <YAJg5MB/Qn5dRqmu@mtj.duckdns.org>
Date:   Fri, 15 Jan 2021 22:43:32 -0500
From:   Tejun Heo <tj@...nel.org>
To:     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,
        borntraeger@...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 v4 1/2] cgroup: svm: Add Encryption ID controller

On Fri, Jan 15, 2021 at 02:18:40PM -0800, Vipin Sharma wrote:
> > * Why is .sev a separate namespace? Isn't the controller supposed to cover
> >   encryption ids across different implementations? It's not like multiple
> >   types of IDs can be in use on the same machine, right?
> > 
> 
> On AMD platform we have two types SEV and SEV-ES which can exists
> simultaneously and they have their own quota.

Can you please give a brief explanation of the two and lay out a scenario
where the two are being used / allocated disjointly?

> > > Other ID types can be easily added in the controller in the same way.
> > 
> > I'm not sure this is necessarily a good thing.
> 
> This is to just say that when Intel and PowerPC changes are ready it
> won't be difficult for them to add their controller.

I'm not really enthused about having per-hardware-type control knobs. None
of other controllers behave that way. Unless it can be abstracted into
something common, I'm likely to object.

> > > +static int enc_id_cg_stat_show(struct seq_file *sf, void *v)
> > > +{
> > > +	unsigned long flags;
> > > +	enum encryption_id_type type = seq_cft(sf)->private;
> > > +
> > > +	spin_lock_irqsave(&enc_id_cg_lock, flags);
> > > +
> > > +	seq_printf(sf, "total %u\n", enc_id_capacity[type]);
> > > +	seq_printf(sf, "used %u\n", root_cg.res[type].usage);
> > 
> > Dup with .current and no need to show total on every cgroup, right?
> 
> This is for the stat file which will only be seen in the root cgroup
> directory.  It is to know overall picture for the resource, what is the
> total capacity and what is the current usage. ".current" file is not
> shown on the root cgroup.

Ah, missed the flags. It's odd for the usage to be presented in two
different ways tho. I think it'd make more sense w/ cgroup.current at root
level. Is the total number available somewhere else in the system?

Thanks.

-- 
tejun