Re: [PATCH v7 00/14] KVM: mm: fd-based approach for supporting KVM guest private memory

[Andy Lutomirski]

On 8/18/22 06:24, Kirill A . Shutemov wrote:
> On Wed, Aug 17, 2022 at 10:40:12PM -0700, Hugh Dickins wrote:
> > On Wed, 6 Jul 2022, Chao Peng wrote:
> > > This is the v7 of this series which tries to implement the fd-based KVM
> > > guest private memory.
> >
> > Here at last are my reluctant thoughts on this patchset.
> >
> > fd-based approach for supporting KVM guest private memory: fine.
> >
> > Use or abuse of memfd and shmem.c: mistaken.
> >
> > memfd_create() was an excellent way to put together the initial prototype.
> >
> > But since then, TDX in particular has forced an effort into preventing
> > (by flags, seals, notifiers) almost everything that makes it shmem/tmpfs.
> >
> > Are any of the shmem.c mods useful to existing users of shmem.c? No.
> > Is MFD_INACCESSIBLE useful or comprehensible to memfd_create() users? No.
> >
> > What use do you have for a filesystem here?  Almost none.
> > IIUC, what you want is an fd through which QEMU can allocate kernel
> > memory, selectively free that memory, and communicate fd+offset+length
> > to KVM.  And perhaps an interface to initialize a little of that memory
> > from a template (presumably copied from a real file on disk somewhere).
> >
> > You don't need shmem.c or a filesystem for that!
> >
> > If your memory could be swapped, that would be enough of a good reason
> > to make use of shmem.c: but it cannot be swapped; and although there
> > are some references in the mailthreads to it perhaps being swappable
> > in future, I get the impression that will not happen soon if ever.
> >
> > If your memory could be migrated, that would be some reason to use
> > filesystem page cache (because page migration happens to understand
> > that type of memory): but it cannot be migrated.
>
> Migration support is in pipeline. It is part of TDX 1.5 [1]. And swapping
> theoretically possible, but I'm not aware of any plans as of now.
>
> [1] https://www.intel.com/content/www/us/en/developer/articles/technical/intel-trust-domain-extensions.html

This thing?

https://cdrdv2.intel.com/v1/dl/getContent/733578

That looks like migration between computers, not between NUMA nodes.  Or 
am I missing something?