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

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Date:   Sun, 1 Oct 2023 23:25:34 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        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 Fri, Sep 29, 2023 at 09:06:34AM -0700, Sean Christopherson wrote:
> KVM needs to be aware of non-refcounted struct page memory no matter what; see
> CVE-2021-22543 and, commit f8be156be163 ("KVM: do not allow mapping valid but
> non-reference-counted pages").  I don't think it makes any sense whatsoever to
> remove that code and assume every driver in existence will do the right thing.

Agreed.

> 
> 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.