linux-kernel - Re: Rename restrictedmem => guardedmem? (was: Re: [PATCH v10 0/9] KVM: mm: fd-based approach for supporting KVM)

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Message-ID: <ZEAGIe7m4lWW5mV+@google.com>
Date:   Wed, 19 Apr 2023 08:17:53 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     Chao Peng <chao.p.peng@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "Maciej S . Szmigiero" <mail@...iej.szmigiero.name>,
        Vlastimil Babka <vbabka@...e.cz>,
        Vishal Annapurve <vannapurve@...gle.com>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        dhildenb@...hat.com, Quentin Perret <qperret@...gle.com>,
        tabba@...gle.com, Michael Roth <michael.roth@....com>,
        wei.w.wang@...el.com, Mike Rapoport <rppt@...nel.org>,
        Liam Merwick <liam.merwick@...cle.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Ackerley Tng <ackerleytng@...gle.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Rename restrictedmem => guardedmem? (was: Re: [PATCH v10 0/9]
 KVM: mm: fd-based approach for supporting KVM)

On Wed, Apr 19, 2023, David Hildenbrand wrote:
> On 19.04.23 02:47, Sean Christopherson wrote:
> > On Tue, Apr 18, 2023, David Hildenbrand wrote:
> > > "memfd_vm" / "vm_mem" would be sooo (feel free to add some more o's here)
> > > much easier to get. It's a special fd to be used to back VM memory. Depending
> > > on the VM type (encrypted/protected/whatever), restrictions might apply (not
> > > able to mmap, not able to read/write ...). For example, there really is no
> > > need to disallow mmap/read/write when using that memory to back a simple VM
> > > where all we want to do is avoid user-space page tables.
> > 
> > In seriousness, I do agree with Jason's very explicit objection[2] against naming
> > a non-KVM uAPI "guest", or any variation thereof.
> 
> While I agree, it's all better than the naming we use right now ...
> 
> 
> Let me throw "tee_mem" / "memfd_tee" into the picture. That could eventually
> catch what we want to have.
> 
> Or "coco_mem" / "memfd_coco".
> 
> Of course, both expect that people know the terminology (just like what "vm"
> stands for), but it's IMHO significantly better than
> restricted/guarded/opaque/whatsoever.
> 
> Again, expresses what it's used for, not why it behaves in weird ways.

I don't want to explicitly tie this to trusted execution or confidential compute,
as there is value in backing "normal" guests with memory that cannot be accessed
by the host userspace without jumping through a few extra hoops, e.g. to add a
layer of protection against data corruption due to host userspace bugs.

> > (b) if another use case comes along, e.g. the Gunyah hypervisor[4][5], we risk
> > someone reinventing a similar solution.
> 
> I agree. But if it's as simple as providing an ioctl for that hypervisor
> that simply wires up the existing implementation, it's not too bad.

Yeah, my mind was wandering in this direction too.  The absolute worst case
scenario seems to be that we do end up creating a generic syscall that is a
superset of KVM's functionality, in which case KVM would end up with an ioctl()
that is just a redirect/wrapper.