netdev - Re: [PATCH net-next v6 08/12] net: homa: create homa

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Message-ID: <CAGXJAmzEn=pGfRcR+xA41pYLUZb8kU0o_4WHvf=dw9t=W6rQ_A@mail.gmail.com>
Date: Tue, 4 Feb 2025 13:20:15 -0800
From: John Ousterhout <ouster@...stanford.edu>
To: Andrew Lunn <andrew@...n.ch>
Cc: Paolo Abeni <pabeni@...hat.com>, Netdev <netdev@...r.kernel.org>, 
	Eric Dumazet <edumazet@...gle.com>, Simon Horman <horms@...nel.org>, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net-next v6 08/12] net: homa: create homa_incoming.c

On Tue, Feb 4, 2025 at 11:41 AM Andrew Lunn <andrew@...n.ch> wrote:
>
> > > If unprivileged applications could use unlimited amount of kernel
> > > memory, they could hurt the whole system stability, possibly causing
> > > functional issue of core kernel due to ENOMEM.
> > >
> > > The we always try to bound/put limits on amount of kernel memory
> > > user-space application can use.
> >
> > Homa's receive buffer space is *not kernel memory*; it's just a large
> > mmapped region created by the application., no different from an
> > application allocating a large region of memory for its internal
> > computation.
>
> ulimit -v should be able to limit this, if user space is doing the
> mmap(). It should be easy to test. Set a low enough limit the mmap()
> should fail, and i guess you get MAP_FAILED and errno = ENOMEM?

I just tried this, and yes, if ulimt -v is set low enough, user apps
can't mmap buffer space to pass to Homa.

-John-