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

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Date: Wed, 13 Mar 2024 06:33:41 -0700
From: Christoph Hellwig <hch@...radead.org>
To: David Stevens <stevensd@...omium.org>
Cc: Christoph Hellwig <hch@...radead.org>,
	Christian Koenig <christian.koenig@....com>,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.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 Wed, Mar 13, 2024 at 01:55:20PM +0900, David Stevens wrote:
> On Thu, Feb 29, 2024 at 10:36 PM Christoph Hellwig <hch@...radead.org> wrote:
> >
> > On Thu, Feb 29, 2024 at 11:57:51AM +0900, David Stevens wrote:
> > > Our use case is virtio-gpu blob resources [1], which directly map host
> > > graphics buffers into the guest as "vram" for the virtio-gpu device.
> > > This feature currently does not work on systems using the amdgpu driver,
> > > as that driver allocates non-compound higher order pages via
> > > ttm_pool_alloc_page().
> >
> > .. and just as last time around that is still the problem that needs
> > to be fixed instead of creating a monster like this to map
> > non-refcounted pages.
> >
> 
> Patches to amdgpu to have been NAKed [1] with the justification that
> using non-refcounted pages is working as intended and KVM is in the
> wrong for wanting to take references to pages mapped with VM_PFNMAP
> [2].

So make them not work for KVM as they should to kick the amdgpu
maintainers a***es.