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

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Date:   Thu, 21 Jan 2021 10:55:13 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Vipin Sharma <vipinsh@...gle.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

Hello,

On Thu, Jan 21, 2021 at 08:55:07AM -0600, Tom Lendacky wrote:
> The hardware will allow any SEV capable ASID to be run as SEV-ES, however,
> the SEV firmware will not allow the activation of an SEV-ES VM to be
> assigned to an ASID greater than or equal to the SEV minimum ASID value. The
> reason for the latter is to prevent an !SEV-ES ASID starting out as an
> SEV-ES guest and then disabling the SEV-ES VMCB bit that is used by VMRUN.
> This would result in the downgrading of the security of the VM without the
> VM realizing it.
> 
> As a result, you have a range of ASIDs that can only run SEV-ES VMs and a
> range of ASIDs that can only run SEV VMs.

I see. That makes sense. What's the downside of SEV-ES compared to SEV w/o
ES? Are there noticeable performance / feature penalties or is the split
mostly for backward compatibility?

Thanks.

-- 
tejun