linux-kernel - Re: [PATCH] KVM: x86: switch hugepage recovery thread to vhost

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Message-ID: <CABgObfYUztpGfBep4ewQXUVJ2vqG_BLrn7c19srBoiXbV+O3+w@mail.gmail.com>
Date: Thu, 19 Dec 2024 21:30:16 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Keith Busch <kbusch@...nel.org>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org, 
	michael.christie@...cle.com, Tejun Heo <tj@...nel.org>, 
	Luca Boccassi <bluca@...ian.org>
Subject: Re: [PATCH] KVM: x86: switch hugepage recovery thread to vhost_task

On Thu, Dec 19, 2024 at 7:09 PM Keith Busch <kbusch@...nel.org> wrote:
> > Is crosvm trying to do anything but exec?  If not, it should probably use the
> > flag.
>
> Good point, and I'm not sure right now. I don't think I know any crosvm
> developer experts but I'm working on that to get a better explanation of
> what's happening,

Ok, I found the code and it doesn't exec (e.g.
https://github.com/google/crosvm/blob/b339d3d7/src/crosvm/sys/linux/jail_warden.rs#L122),
so that's not an option. Well, if I understand correctly from a
cursory look at the code, crosvm is creating a jailed child process
early, and then spawns further jails through it; so it's just this
first process that has to cheat.

One possibility on the KVM side is to delay creating the vhost_task
until the first KVM_RUN. I don't like it but...

I think we should nevertheless add something to the status file in
procfs, that makes it easy to detect kernel tasks (PF_KTHREAD |
PF_IO_WORKER | PF_USER_WORKER).

Paolo