linux-kernel - Re: [RFC PATCH 10/30] vfio/pci: Export vfio dma-buf specific info for importers

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Message-ID: <20250602133009.GC233377@nvidia.com>
Date: Mon, 2 Jun 2025 10:30:09 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: Xu Yilun <yilun.xu@...ux.intel.com>
Cc: kvm@...r.kernel.org, sumit.semwal@...aro.org, christian.koenig@....com,
	pbonzini@...hat.com, seanjc@...gle.com, alex.williamson@...hat.com,
	dan.j.williams@...el.com, aik@....com, linux-coco@...ts.linux.dev,
	dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, vivek.kasireddy@...el.com,
	yilun.xu@...el.com, linux-kernel@...r.kernel.org, lukas@...ner.de,
	yan.y.zhao@...el.com, daniel.vetter@...ll.ch, leon@...nel.org,
	baolu.lu@...ux.intel.com, zhenzhong.duan@...el.com,
	tao1.su@...el.com, linux-pci@...r.kernel.org, zhiw@...dia.com,
	simona.vetter@...ll.ch, shameerali.kolothum.thodi@...wei.com,
	aneesh.kumar@...nel.org, iommu@...ts.linux.dev,
	kevin.tian@...el.com
Subject: Re: [RFC PATCH 10/30] vfio/pci: Export vfio dma-buf specific info
 for importers

On Thu, May 29, 2025 at 01:34:53PM +0800, Xu Yilun wrote:
> Export vfio dma-buf specific info by attaching vfio_dma_buf_data in
> struct dma_buf::priv. Provide a helper vfio_dma_buf_get_data() for
> importers to fetch these data. Exporters identify VFIO dma-buf by
> successfully getting these data.
> 
> VFIO dma-buf supports disabling host access to these exported MMIO
> regions when the device is converted to private. Exporters like KVM
> need to identify this type of dma-buf to decide if it is good to use.
> KVM only allows host unaccessible MMIO regions been mapped in private
> roots.
> 
> Export struct kvm * handler attached to the vfio device. This
> allows KVM to do another sanity check. MMIO should only be assigned to
> a CoCo VM if its owner device is already assigned to the same VM.

This doesn't seem right, it should be encapsulated into the standard
DMABUF API in some way.

Jason