linux-kernel - Re: [RFC PATCH 00/12] Private MMIO support for private assigned dev

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Message-ID: <aB4tQHmHzHooDeTE@yilunxu-OptiPlex-7050>
Date: Sat, 10 May 2025 00:28:48 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Alexey Kardashevskiy <aik@....com>
Cc: 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,
	jgg@...dia.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, baolu.lu@...ux.intel.com,
	zhenzhong.duan@...el.com, tao1.su@...el.com
Subject: Re: [RFC PATCH 00/12] Private MMIO support for private assigned dev

On Fri, May 09, 2025 at 07:12:46PM +0800, Xu Yilun wrote:
> On Fri, May 09, 2025 at 01:04:58PM +1000, Alexey Kardashevskiy wrote:
> > Ping?
> 
> Sorry for late reply from vacation.
> 
> > Also, since there is pushback on 01/12 "dma-buf: Introduce dma_buf_get_pfn_unlocked() kAPI", what is the plan now? Thanks,
> 
> As disscussed in the thread, this kAPI is not well considered but IIUC
> the concept of "importer mapping" is still valid. We need more
> investigation about all the needs - P2P, CC memory, private bus
> channel, and work out a formal API.
> 
> However in last few months I'm focusing on high level TIO flow - TSM
> framework, IOMMUFD based bind/unbind, so no much progress here and is
> still using this temporary kAPI. But as long as "importer mapping" is
> alive, the dmabuf fd for KVM is still valid and we could enable TIO
> based on that.

Oh I forgot to mention I moved the dmabuf creation from VFIO to IOMMUFD
recently, the IOCTL is against iommufd_device. According to Jason's
opinion [1], TSM bind/unbind should be called against iommufd_device,
then I need to do the same for dmabuf.  This is because Intel TDX
Connect enforces a specific operation sequence between TSM unbind & MMIO
unmap:

  1. STOP TDI via TDISP message STOP_INTERFACE
  2. Private MMIO unmap from Secure EPT
  3. Trusted Device Context Table cleanup for the TDI
  4. TDI ownership reclaim and metadata free

That makes TSM unbind & dmabuf closely correlated and should be managed
by the same kernel component.

IIUC, the suggested flow is VFIO receives a CC capable flag and propagate
to IOMMUFD, which means VFIO hand over device's MMIO management & CC
management to IOMMUFD.

[1]: https://lore.kernel.org/all/20250306182614.GF354403@ziepe.ca/

Thanks,
Yilun