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

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Date:   Tue, 15 Sep 2020 10:32:02 -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 Tue, Sep 15, 2020 at 12:22:05PM -0500, Tom Lendacky wrote:
> 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@....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.

But isn't guest memory inaccessible for SEV?  E.g. how does KVM emulate the
save/restore to/from SMRAM?