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

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Message-ID: <b896ea83-7b98-7c86-f147-446faf2dbc44@linux.ibm.com>
Date:   Mon, 28 Sep 2020 11:12:58 +0200
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vipin Sharma <vipinsh@...gle.com>
Cc:     thomas.lendacky@....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,
        "kvm-ppc@...r.kernel.org" <kvm-ppc@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        Paul Mackerras <paulus@...abs.org>,
        Christian Borntraeger <borntraeger@...ibm.com>
Subject: Re: [RFC Patch 0/2] KVM: SVM: Cgroup support for SVM SEV ASIDs

On 9/23/20 2:47 PM, Paolo Bonzini wrote:
> On 22/09/20 03:48, Sean Christopherson wrote:
>> This should be genericized to not be SEV specific.  TDX has a similar
>> scarcity issue in the form of key IDs, which IIUC are analogous to SEV ASIDs
>> (gave myself a quick crash course on SEV ASIDs).  Functionally, I doubt it
>> would change anything, I think it'd just be a bunch of renaming.  The hardest
>> part would probably be figuring out a name :-).
>>
>> Another idea would be to go even more generic and implement a KVM cgroup
>> that accounts the number of VMs of a particular type, e.g. legacy, SEV,
>> SEV-ES?, and TDX.  That has potential future problems though as it falls
>> apart if hardware every supports 1:MANY VMs:KEYS, or if there is a need to
>> account keys outside of KVM, e.g. if MKTME for non-KVM cases ever sees the
>> light of day.
> 
> Or also MANY:1 (we are thinking of having multiple VMs share the same
> SEV ASID).
> 
> It might even be the same on s390 and PPC, in which case we probably
> want to implement this in virt/kvm.  Paul, Janosch, do you think this
> would make sense for you?  The original commit message is below.
> 
> Paolo
> 
>> On Mon, Sep 21, 2020 at 05:40:22PM -0700, Vipin Sharma wrote:
>>> Hello,
>>>
>>> This patch series adds a new SEV controller for tracking and limiting
>>> the usage of SEV ASIDs on the AMD SVM platform.
>>>
>>> SEV ASIDs are used in creating encrypted VM and lightweight sandboxes
>>> but this resource is in very limited quantity on a host.
>>>
>>> This limited quantity creates issues like SEV ASID starvation and
>>> unoptimized scheduling in the cloud infrastructure.
>>>
>>> SEV controller provides SEV ASID tracking and resource control
>>> mechanisms.
> 

On s390 we currently support a few million protected guests per LPAR so
guest IDs are not exactly scarce. However having accounting for them
might add some value nevertheless, especially when having large amount
of protected containers.

@Christian: Any thoughts on this?



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