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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <cc3e88df-0c6e-2a8c-80aa-4dc3f0d8cea9@amd.com>
Date:   Thu, 1 Oct 2020 17:44:08 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vipin Sharma <vipinsh@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>, tj@...nel.org,
        lizefan@...wei.com, Joerg Roedel <joro@...tes.org>, corbet@....net,
        "Singh, Brijesh" <brijesh.singh@....com>,
        "Grimm, Jon" <jon.grimm@....com>, eric.vantassell@....com,
        Matt Gingell <gingell@...gle.com>,
        David Rientjes <rientjes@...gle.com>,
        kvm list <kvm@...r.kernel.org>, x86@...nel.org,
        cgroups@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC Patch 0/2] KVM: SVM: Cgroup support for SVM SEV ASIDs

On 10/1/20 1:08 PM, Peter Gonda wrote:
> On Thu, Sep 24, 2020 at 1:55 PM Tom Lendacky <thomas.lendacky@....com> wrote:
>>
>> On 9/24/20 2:21 PM, Sean Christopherson wrote:
>>> On Tue, Sep 22, 2020 at 02:14:04PM -0700, Vipin Sharma wrote:
>>>> On Mon, Sep 21, 2020 at 06:48:38PM -0700, Sean Christopherson wrote:
>>>>> 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.
>>>>>
>>>>> 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.
>>>>
>>>> I read about the TDX and its use of the KeyID for encrypting VMs. TDX
>>>> has two kinds of KeyIDs private and shared.
>>>
>>> To clarify, "shared" KeyIDs are simply legacy MKTME KeyIDs.  This is relevant
>>> because those KeyIDs can be used without TDX or KVM in the picture.
>>>
>>>> On AMD platform there are two types of ASIDs for encryption.
>>>> 1. SEV ASID - Normal runtime guest memory encryption.
>>>> 2. SEV-ES ASID - Extends SEV ASID by adding register state encryption with
>>>>                integrity.
>>>>
>>>> Both types of ASIDs have their own maximum value which is provisioned in
>>>> the firmware
>>>
>>> Ugh, I missed that detail in the SEV-ES RFC.  Does SNP add another ASID type,
>>> or does it reuse SEV-ES ASIDs?  If it does add another type, is that trend
>>> expected to continue, i.e. will SEV end up with SEV, SEV-ES, SEV-ES-SNP,
>>> SEV-ES-SNP-X, SEV-ES-SNP-X-Y, etc...?
>>
>> SEV-SNP and SEV-ES share the same ASID range.
> 
> Where is this documented? From the SEV-SNP FW ABI Spec 0.8 "The
> firmware checks that ASID is an encryption capable ASID. If not, the
> firmware returns INVALID_ASID." that doesn't seem clear that an SEV-ES
> ASID is required. Should this document be more clear?

I let the owner of the spec know and it will be updated.

Thanks,
Tom

>