linux-kernel - Re: [PATCH v9 0/6] KVM: allow mapping non-refcounted pages

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Date: Mon, 5 Feb 2024 19:29:32 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: David Stevens <stevensd@...omium.org>, Yu Zhang <yu.c.zhang@...ux.intel.com>, 
	Isaku Yamahata <isaku.yamahata@...il.com>, Zhi Wang <zhi.wang.linux@...il.com>, 
	kvmarm@...ts.linux.dev, linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v9 0/6] KVM: allow mapping non-refcounted pages

On Sun, Oct 01, 2023, Christoph Hellwig wrote:
> On Fri, Sep 29, 2023 at 09:06:34AM -0700, Sean Christopherson wrote:
> > With the cleanups done, playing nice with non-refcounted paged instead of outright
> > rejecting them is a wash in terms of lines of code, complexity, and ongoing
> > maintenance cost.
> 
> I tend to strongly disagree with that, though.  We can't just let these
> non-refcounted pages spread everywhere and instead need to fix their
> usage.

Sorry for the horrifically slow reply.

Is there a middle ground somewhere between allowing this willy nilly, and tainting
the kernel?  I too would love to get the TTM stuff fixed up, but every time I look
at that code I am less and less confident that it will happen anytime soon.  It's
not even clear to me what all code needs to be touched.

In other words, is there a way we can unblock David and friends, while still
providing a forcing function of some kind to motivate/heckle the TTM (or whatever
is making the allocations) to change?