linux-kernel - Re: [RFC PATCH 19/30] vfio/pci: Add TSM TDI bind/unbind IOCTLs for TEE-IO support

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Message-ID: <20250605163339.GE19710@nvidia.com>
Date: Thu, 5 Jun 2025 13:33:39 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>
Cc: Xu Yilun <yilun.xu@...ux.intel.com>, 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,
	iommu@...ts.linux.dev, kevin.tian@...el.com
Subject: Re: [RFC PATCH 19/30] vfio/pci: Add TSM TDI bind/unbind IOCTLs for
 TEE-IO support

On Thu, Jun 05, 2025 at 09:47:01PM +0530, Aneesh Kumar K.V wrote:
> Jason Gunthorpe <jgg@...dia.com> writes:
> 
> > On Thu, Jun 05, 2025 at 05:33:52PM +0530, Aneesh Kumar K.V wrote:
> >
> >> > +
> >> > +	/* To ensure no host side MMIO access is possible */
> >> > +	ret = pci_request_regions_exclusive(pdev, "vfio-pci-tsm");
> >> > +	if (ret)
> >> > +		goto out_unlock;
> >> > +
> >> >
> >> 
> >> I am hitting failures here with similar changes. Can you share the Qemu
> >> changes needed to make this pci_request_regions_exclusive successful.
> >> Also after the TDI is unbound, we want the region ownership backto
> >> "vfio-pci" so that things continue to work as non-secure device. I don't
> >> see we doing that. I could add a pci_bar_deactivate/pci_bar_activate in
> >> userspace which will result in vfio_unmap()/vfio_map(). But that doesn't
> >> release the region ownership.
> >
> > Again, IMHO, we should not be doing this dynamically. VFIO should do
> > pci_request_regions_exclusive() once at the very start and it should
> > stay that way.
> >
> > There is no reason to change it dynamically.
> >
> > The only decision to make is if all vfio should switch to exclusive
> > mode or if we need to make it optional for userspace.
> 
> We only need the exclusive mode when the device is operating in secure
> mode, correct? That suggests we’ll need to dynamically toggle this
> setting based on the device’s security state.

No, if the decision is that VFIO should allow this to be controlled by
userspace then userspace will tell iommufd to run in regions_exclusive
mode prior to opening the vfio cdev and VFIO will still do it once at
open time and never change it.

The only thing request_regions does is block other drivers outside
vfio from using this memory space. There is no reason at all to change
this dynamically. A CC VMM using VFIO will never use a driver outside
VFIO to touch the VFIO controlled memory.

Jason