linux-kernel - Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL

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Date:   Fri, 19 Nov 2021 15:47:46 -0400
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     David Hildenbrand <david@...hat.com>,
        Chao Peng <chao.p.peng@...ux.intel.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, qemu-devel@...gnu.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Hugh Dickins <hughd@...gle.com>,
        Jeff Layton <jlayton@...nel.org>,
        "J . Bruce Fields" <bfields@...ldses.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Yu Zhang <yu.c.zhang@...ux.intel.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        luto@...nel.org, john.ji@...el.com, susie.li@...el.com,
        jun.nakajima@...el.com, dave.hansen@...el.com, ak@...ux.intel.com
Subject: Re: [RFC v2 PATCH 01/13] mm/shmem: Introduce F_SEAL_GUEST

On Fri, Nov 19, 2021 at 07:18:00PM +0000, Sean Christopherson wrote:
> On Fri, Nov 19, 2021, David Hildenbrand wrote:
> > On 19.11.21 16:19, Jason Gunthorpe wrote:
> > > As designed the above looks useful to import a memfd to a VFIO
> > > container but could you consider some more generic naming than calling
> > > this 'guest' ?
> > 
> > +1 the guest terminology is somewhat sob-optimal.
> 
> For the F_SEAL part, maybe F_SEAL_UNMAPPABLE?

Perhaps INACCESSIBLE?

> No ideas for the kernel API, but that's also less concerning since
> it's not set in stone.  I'm also not sure that dedicated APIs for
> each high-ish level use case would be a bad thing, as the semantics
> are unlikely to be different to some extent.  E.g. for the KVM use
> case, there can be at most one guest associated with the fd, but
> there can be any number of VFIO devices attached to the fd.

Even the kvm thing is not a hard restriction when you take away
confidential compute.

Why can't we have multiple KVMs linked to the same FD if the memory
isn't encrypted? Sure it isn't actually useful but it should work
fine.

Supporting only one thing is just a way to avoid having a linked list
of clients to broadcast invalidations too - for instance by using a
standard notifier block...

Also, how does dirty tracking work on this memory?

Jason