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Date: Thu, 28 Sep 2023 22:19:36 -0700
From: Christoph Hellwig <hch@infradead.org>
To: David Stevens <stevensd@chromium.org>
Cc: Sean Christopherson <seanjc@google.com>,
	Yu Zhang <yu.c.zhang@linux.intel.com>,
	Isaku Yamahata <isaku.yamahata@gmail.com>,
	Zhi Wang <zhi.wang.linux@gmail.com>, kvmarm@lists.linux.dev,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH v9 0/6] KVM: allow mapping non-refcounted pages
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On Mon, Sep 11, 2023 at 11:16:30AM +0900, David Stevens wrote:
> From: David Stevens <stevensd@chromium.org>
> 
> This patch series adds support for mapping VM_IO and VM_PFNMAP memory
> that is backed by struct pages that aren't currently being refcounted
> (e.g. tail pages of non-compound higher order allocations) into the
> guest.
> 
> 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.
> 
> First, this series replaces the __gfn_to_pfn_memslot API with a more
> extensible __kvm_faultin_pfn API. The updated API rearranges
> __gfn_to_pfn_memslot's args into a struct and where possible packs the
> bool arguments into a FOLL_ flags argument. The refactoring changes do
> not change any behavior.

Instead of adding hacks to kvm you really should fix the driver / TTM
to not do weird memory allocations.