linux-kernel - Re: [RFC Patch 1/2] KVM: SVM: Create SEV cgroup controller.

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Date:   Tue, 22 Sep 2020 09:05:08 -0700
From:   Vipin Sharma <vipinsh@...gle.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Randy Dunlap <rdunlap@...radead.org>, thomas.lendacky@....com,
        pbonzini@...hat.com, tj@...nel.org, lizefan@...wei.com,
        joro@...tes.org, corbet@....net, brijesh.singh@....com,
        jon.grimm@....com, eric.vantassell@....com, gingell@...gle.com,
        rientjes@...gle.com, kvm@...r.kernel.org, x86@...nel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Dionna Glaze <dionnaglaze@...gle.com>,
        Erdem Aktas <erdemaktas@...gle.com>
Subject: Re: [RFC Patch 1/2] KVM: SVM: Create SEV cgroup controller.

On Mon, Sep 21, 2020 at 06:22:28PM -0700, Sean Christopherson wrote:
> On Mon, Sep 21, 2020 at 06:04:04PM -0700, Randy Dunlap wrote:
> > Hi,
> > 
> > On 9/21/20 5:40 PM, Vipin Sharma wrote:
> > > diff --git a/init/Kconfig b/init/Kconfig
> > > index d6a0b31b13dc..1a57c362b803 100644
> > > --- a/init/Kconfig
> > > +++ b/init/Kconfig
> > > @@ -1101,6 +1101,20 @@ config CGROUP_BPF
> > >  	  BPF_CGROUP_INET_INGRESS will be executed on the ingress path of
> > >  	  inet sockets.
> > >  
> > > +config CGROUP_SEV
> > > +	bool "SEV ASID controller"
> > > +	depends on KVM_AMD_SEV
> > > +	default n
> > > +	help
> > > +	  Provides a controller for AMD SEV ASIDs. This controller limits and
> > > +	  shows the total usage of SEV ASIDs used in encrypted VMs on AMD
> > > +	  processors. Whenever a new encrypted VM is created using SEV on an
> > > +	  AMD processor, this controller will check the current limit in the
> > > +	  cgroup to which the task belongs and will deny the SEV ASID if the
> > > +	  cgroup has already reached its limit.
> > > +
> > > +	  Say N if unsure.
> > 
> > Something here (either in the bool prompt string or the help text) should
> > let a reader know w.t.h. SEV means.
> > 
> > Without having to look in other places...
> 
> ASIDs too.  I'd also love to see more info in the docs and/or cover letter
> to explain why ASID management on SEV requires a cgroup.  I know what an
> ASID is, and have a decent idea of how KVM manages ASIDs for legacy VMs, but
> I know nothing about why ASIDs are limited for SEV and not legacy VMs.

Thanks for the feedback, I will add more details in the Kconfig and the
documentation about SEV and ASID.