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

From: Tom Lendacky <thomas.lendacky@amd.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	x86@kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [RFC PATCH 00/35] SEV-ES hypervisor support
Date: Tue, 15 Sep 2020 12:22:05 -0500	[thread overview]
Message-ID: <bee6fdda-d548-8af5-f029-25c22165bf84@amd.com> (raw)
In-Reply-To: <20200914225951.GM7192@sjchrist-ice>

On 9/14/20 5:59 PM, Sean Christopherson wrote:
> On Mon, Sep 14, 2020 at 03:15:14PM -0500, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.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?).

Right, SMM isn't currently supported under SEV-ES. SEV does support SMM,
though, since the register state can be altered to change over to the SMM
register state. So the SMI ioctl() is ok for SEV.

> 
> 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.

That sounds good.

Thanks,
Tom

> 
> Thanks!
> 
> 
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