linux-kernel - Re: [PATCH v11 0/8] KVM: allow mapping non-refcounted pages

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Date: Mon, 18 Mar 2024 16:20:39 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Paolo Bonzini <pbonzini@...hat.com>
Cc: Christoph Hellwig <hch@...radead.org>,
	Christian König <christian.koenig@....com>,
	David Stevens <stevensd@...omium.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Yu Zhang <yu.c.zhang@...ux.intel.com>,
	Isaku Yamahata <isaku.yamahata@...il.com>,
	Zhi Wang <zhi.wang.linux@...il.com>,
	Maxim Levitsky <mlevitsk@...hat.com>, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v11 0/8] KVM: allow mapping non-refcounted pages

On Mon, Mar 18, 2024 at 02:10:55PM +0100, Paolo Bonzini wrote:
> Another possibility is to have a double-underscore version that allows
> FOLL_GET, and have the "clean" kvm_follow_pfn() forbid it. So you
> would still have the possibility to convert to __kvm_follow_pfn() with
> FOLL_GET first, and then when you remove the refcount you switch to
> kvm_follow_pfn().

That does sound much better.  Then again anything that actually wants
pages (either for a good reason or historic reasons) really should be
using get/pin_user_pages anyway and not use follow_pte.