Re: [PATCH V4 1/1] KVM: TDX: Add sub-ioctl KVM_TDX_TERMINATE_VM

[Vishal Annapurve]

On Fri, Jun 20, 2025 at 11:59 AM Edgecombe, Rick P
<rick.p.edgecombe@xxxxxxxxx> wrote:
>
> On Fri, 2025-06-20 at 07:24 -0700, Sean Christopherson wrote:
> > > The patch was tested with QEMU which AFAICT does not touch  memslots when
> > > shutting down.  Is there a reason to?
> >
> > In this case, the VMM process is not shutting down.  To emulate a reboot, the
> > VMM destroys the VM, but reuses the guest_memfd files for the "new" VM.
> > Because guest_memfd takes a reference to "struct kvm", through memslot
> > bindings, memslots need to be manually destroyed so that all references are
> > put and the VM is freed by the kernel.
>
> Sorry if I'm being dumb, but why does it do this? It saves freeing/allocating
> the guestmemfd pages? Or the in-place data gets reused somehow?

The goal is just to be able to reuse the same physical memory for the
next boot of the guest. Freeing and faulting-in the same amount of
memory is redundant and time-consuming for large VM sizes.

>
> The series Vishal linked has some kind of SEV state transfer thing. How is it
> intended to work for TDX?

The series[1] unblocks intrahost-migration [2] and reboot usecases.

[1] https://lore.kernel.org/lkml/cover.1747368092.git.afranji@xxxxxxxxxx/#t
[2] https://lore.kernel.org/lkml/cover.1749672978.git.afranji@xxxxxxxxxx/#t

>
> >   E.g. otherwise multiple reboots would manifest as memory leakds and
> > eventually OOM the host.
>
> This is in the case of future guestmemfd functionality? Or today?

Intrahost-migration and guest reboot are important usecases for Google
to support guest VM lifecycles.