Received-SPF: softfail (google.com: domain of transitioning linux-kernel-owner@vger.kernel.org does not designate 23.128.96.19 as permitted sender) client-ip=23.128.96.19;
Date:   Thu, 7 Apr 2022 20:50:29 -0700
From:   Isaku Yamahata <isaku.yamahata@gmail.com>
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     isaku.yamahata@intel.com, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com,
        Jim Mattson <jmattson@google.com>, erdemaktas@google.com,
        Connor Kuehl <ckuehl@redhat.com>,
        Sean Christopherson <seanjc@google.com>
Subject: Re: [RFC PATCH v5 102/104] KVM: TDX: Add methods to ignore accesses
 to CPU state
Message-ID: <20220408035029.GH2864606@ls.amr.corp.intel.com>
References: <cover.1646422845.git.isaku.yamahata@intel.com>
 <3a278829a8617b86b36c32b68a82bc727013ace8.1646422845.git.isaku.yamahata@intel.com>
 <7ec77c3c-7819-38bb-96ac-ca249e2e0f42@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <7ec77c3c-7819-38bb-96ac-ca249e2e0f42@redhat.com>
Precedence: bulk

On Tue, Apr 05, 2022 at 05:56:36PM +0200,
Paolo Bonzini <pbonzini@redhat.com> wrote:

> On 3/4/22 20:49, isaku.yamahata@intel.com wrote:
> > From: Sean Christopherson <sean.j.christopherson@intel.com>
> > 
> > TDX protects TDX guest state from VMM.  Implements to access methods for
> > TDX guest state to ignore them or return zero.
> > 
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> > Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
> 
> For most of these, it would be interesting to see which paths actually can
> be hit.  For SEV, it's all cut out by
> 
>         if (vcpu->arch.guest_state_protected)
>                 return 0;
> 
> in functions such as __set_sregs_common.  Together with the fact that TDX
> does not get to e.g. handle_set_cr0, this should prevent most such calls
> from happening.  So most of these should be KVM_BUG_ON or WARN_ON, not just
> returns.

If debug mode is enabled, guest state isn't protected.  memory/cpu state can
be read/written via SEAMCALLs.  So guest_state_protected isn't set to true.

Anyway for now with this patch series, debug mode isn't supported well, I will
go with adding KVM_BUG_ON/WARN_ON.
-- 
Isaku Yamahata <isaku.yamahata@gmail.com>