linux-kernel - Re: [RFC PATCH 08/12] vfio/pci: Create host unaccessible dma-buf for private device

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Message-ID: <20250120132843.GI5556@nvidia.com>
Date: Mon, 20 Jan 2025 09:28:43 -0400
From: Jason Gunthorpe <jgg@...dia.com>
To: Alexey Kardashevskiy <aik@....com>
Cc: Baolu Lu <baolu.lu@...ux.intel.com>,
	Xu Yilun <yilun.xu@...ux.intel.com>, kvm@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-media@...r.kernel.org,
	linaro-mm-sig@...ts.linaro.org, sumit.semwal@...aro.org,
	christian.koenig@....com, pbonzini@...hat.com, seanjc@...gle.com,
	alex.williamson@...hat.com, vivek.kasireddy@...el.com,
	dan.j.williams@...el.com, yilun.xu@...el.com,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
	lukas@...ner.de, yan.y.zhao@...el.com, daniel.vetter@...ll.ch,
	leon@...nel.org, zhenzhong.duan@...el.com, tao1.su@...el.com
Subject: Re: [RFC PATCH 08/12] vfio/pci: Create host unaccessible dma-buf for
 private device

On Mon, Jan 20, 2025 at 08:45:51PM +1100, Alexey Kardashevskiy wrote:

> > For CC I'm expecting the KVM fd to be the handle for the cVM, so any
> > RPCs that want to call into the secure world need the KVM FD to get
> > the cVM's identifier. Ie a "bind to cVM" RPC will need the PCI
> > information and the cVM's handle.
> 
> And keep KVM fd open until unbind? Or just for the short time to call the
> PSP?

iommufd will keep the KVM fd alive so long as the vIOMMU object
exists. Other uses for kvm require it to work like this.

> > But it also seems to me that VFIO should be able to support putting
> > the device into the RUN state without involving KVM or cVMs.
> 
> AMD's TDI bind handler in the PSP wants a guest handle ("GCTX") and a guest
> device BDFn, and VFIO has no desire to dive into this KVM business beyond
> IOMMUFD.

As in my other email, VFIO is not restricted to running VMs, useful
things should be available to apps like DPDK.

There is a use case for using TDISP and getting devices up into an
ecrypted/attested state on pure bare metal without any KVM, VFIO
should work in that use case too.

Jason