Re: [GIT PULL] KVM changes for Linux 6.14

Linus Torvalds
2025-01-25T18:32:08Z

On Sat, 25 Jan 2025 at 10:12, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Arguably the user space oddity is just strange and Paolo even calls it
> a bug, but at the same time, I do think user space can and should
> reasonably expect that it only has children that it created
> explicitly [..]

Note that I think that doing things like "io_uring" and getting IO
helper threads that way would very much count as "explicit children",
so I don't argue that all kernel helper threads would fall under this
category.

And I suspect that the normal vhost workers fall under that same kind
of "it's like io_uring". If you use VHOST_NEW_WORKER to create a
worker thread, then that's a pretty explicit "I have a child process".

So it's really just that hugepage recovery thread that seems to be a
bit "too" much of an implicit kernel helper thread that user space
kind of gets accidentally and implicitly just because of a kernel
implementation detail.

I'm sure the kvm hack to just start it later (at KVM_RUN time?) is
sufficient in practice, but it still feels conceptually iffy to me.

Linus