linux-kernel - Re: [RFC PATCH 00/35] SEV-ES hypervisor support

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Date:   Mon, 14 Sep 2020 15:59:52 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [RFC PATCH 00/35] SEV-ES hypervisor support

On Mon, Sep 14, 2020 at 03:15:14PM -0500, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> This patch series provides support for running SEV-ES guests under KVM.

>From the x86/VMX side of things, the GPR hooks are the only changes that I
strongly dislike.

For the vmsa_encrypted flag and related things like allow_debug(), I'd
really like to aim for a common implementation between SEV-ES and TDX[*] from
the get go, within reason obviously.  From a code perspective, I don't think
it will be too onerous as the basic tenets are quite similar, e.g. guest
state is off limits, FPU state is autoswitched, etc..., but I suspect (or
maybe worry?) that there are enough minor differences that we'll want a more
generic way of marking ioctls() as disallowed to avoid having one-off checks
all over the place.

That being said, it may also be that there are some ioctls() that should be
disallowed under SEV-ES, but aren't in this series.  E.g. I assume
kvm_vcpu_ioctl_smi() should be rejected as KVM can't do the necessary
emulation (I assume this applies to vanilla SEV as well?).

One thought to try and reconcile the differences between SEV-ES and TDX would
be expicitly list which ioctls() are and aren't supported and go from there?
E.g. if there is 95% overlap than we probably don't need to get fancy with
generic allow/deny.

Given that we don't yet have publicly available KVM code for TDX, what if I
generate and post a list of ioctls() that are denied by either SEV-ES or TDX,
organized by the denier(s)?  Then for the ioctls() that are denied by one and
not the other, we add a brief explanation of why it's denied?

If that sounds ok, I'll get the list and the TDX side of things posted
tomorrow.

Thanks!

[*] https://software.intel.com/content/www/us/en/develop/articles/intel-trust-domain-extensions.html