> -----Original Message-----
> From: Vishal Annapurve <vannapurve@google.com>
> Sent: Monday, June 19, 2023 2:55 PM
> To: Zhi Wang <zhi.wang.linux@gmail.com>
> Cc: Yamahata, Isaku <isaku.yamahata@intel.com>; kvm@vger.kernel.org;
> linux-kernel@vger.kernel.org; isaku.yamahata@gmail.com; Paolo Bonzini
> <pbonzini@redhat.com>; Aktas, Erdem <erdemaktas@google.com>;
> Christopherson,, Sean <seanjc@google.com>; Shahar, Sagi
> <sagis@google.com>; David Matlack <dmatlack@google.com>; Huang, Kai
> <kai.huang@intel.com>; Chen, Bo2 <chen.bo@intel.com>; linux-
> coco@lists.linux.dev; Chao Peng <chao.p.peng@linux.intel.com>; Ackerley
> Tng <ackerleytng@google.com>; Michael Roth <michael.roth@amd.com>
> Subject: Re: [RFC PATCH 0/6] KVM: guest memory: Misc enhacnement
> 
> On Mon, Jun 19, 2023 at 1:11 PM Zhi Wang <zhi.wang.linux@gmail.com>
> wrote:
> >
> > On Mon, 19 Jun 2023 12:11:50 -0700
> > Vishal Annapurve <vannapurve@google.com> wrote:
> >
> > > On Thu, Jun 15, 2023 at 1:12___PM <isaku.yamahata@intel.com> wrote:
> > > > ...
> > > >
> > > > * VM type: Now we have KVM_X86_PROTECTED_VM. How do we
> proceed?
> > > >   - Keep KVM_X86_PROTECTED_VM for its use. Introduce
> KVM_X86_TDX_VM
> > > >   - Use KVM_X86_PROTECTED_VM for TDX. (If necessary, introduce
> another type in
> > > >     the future)
> > > >   - any other way?
> > >
> > > There are selftests posted[1] in context of this work, which rely on
> > > KVM_X86_PROTECTED_VM being just the software-only
> > > psuedo-confidential VMs. In future there might be more work to
> > > expand this usecase to full-scale VMs. So it would be better to
> > > treat protected VMs as a separate type which can be used on any
> > > platform without the need of enabling TDX/SEV functionality.
> > >
> >
> > Out of curiosity, is this really a valid case in practice except selftest?
> > It sounds to me whenever KVM_X86_PROTECTED_VM is used, it has to be
> > tied with a platform-specific CC type.
> 
> Protected VM effort is about being able to have guest memory ranges not
> mapped into Userspace VMM and so are unreachable for most of the cases
> from KVM as well. Non-CC VMs can use this support to mitigate any
> unintended accesses from userspace VMM/KVM possibly using enlightened
> kernels.

"PROTECTED" seems to be not very close to what you mean here. "PROTECTED_MEM" ?
What case of non-CC VMs may use this feature in reality?  Or do you have any expected cases?

> 
> Exact implementation of such a support warrants more discussion but it
> should be in the line of sight here as a future work item.
> 
> 
> 
> 
> >
> > > TDX VM type can possibly serve as a specialized type of protected VM
> > > with additional arch specific capabilities enabled.
> > >
> > > [1] - https://github.com/sean-jc/linux/commits/x86/kvm_gmem_solo
> >

On Wed, Jun 21, 2023 at 11:20 AM Dong, Eddie <eddie.dong@intel.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Vishal Annapurve <vannapurve@google.com>
> > Sent: Monday, June 19, 2023 2:55 PM
> > To: Zhi Wang <zhi.wang.linux@gmail.com>
> > Cc: Yamahata, Isaku <isaku.yamahata@intel.com>; kvm@vger.kernel.org;
> > linux-kernel@vger.kernel.org; isaku.yamahata@gmail.com; Paolo Bonzini
> > <pbonzini@redhat.com>; Aktas, Erdem <erdemaktas@google.com>;
> > Christopherson,, Sean <seanjc@google.com>; Shahar, Sagi
> > <sagis@google.com>; David Matlack <dmatlack@google.com>; Huang, Kai
> > <kai.huang@intel.com>; Chen, Bo2 <chen.bo@intel.com>; linux-
> > coco@lists.linux.dev; Chao Peng <chao.p.peng@linux.intel.com>; Ackerley
> > Tng <ackerleytng@google.com>; Michael Roth <michael.roth@amd.com>
> > Subject: Re: [RFC PATCH 0/6] KVM: guest memory: Misc enhacnement
> >
> > On Mon, Jun 19, 2023 at 1:11 PM Zhi Wang <zhi.wang.linux@gmail.com>
> > wrote:
> > >
> > > On Mon, 19 Jun 2023 12:11:50 -0700
> ...
> >
> > Protected VM effort is about being able to have guest memory ranges not
> > mapped into Userspace VMM and so are unreachable for most of the cases
> > from KVM as well. Non-CC VMs can use this support to mitigate any
> > unintended accesses from userspace VMM/KVM possibly using enlightened
> > kernels.
>
> "PROTECTED" seems to be not very close to what you mean here. "PROTECTED_MEM" ?
> What case of non-CC VMs may use this feature in reality?  Or do you have any expected cases?
>

Similar to pKvm efforts [1], PROTECTED_VM functionality may be used to
unmap guest memory ranges from the host and userspace VMM on x86
platforms. If the KVM/host kernel and the guest VMs are enlightened
for this usecase, then it should be possible to deploy this feature
for normal VMs irrespective of the platforms they are running on.

Primary usecase here would be to prevent unintended accesses from
KVM/userspace VMM which would normally go undetected at runtime or are
hard to trace back to the original culprit.

[1] https://source.android.com/docs/core/virtualization/architecture#hypervisor