linux-kernel - Re: [PATCH v2 06/19] iommufd/viommu: Add IOMMU_VIOMMU_SET/UNSET_VDEV

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Message-ID: <Zvu4rZosYFjCuEC/@Asurada-Nvidia>
Date: Tue, 1 Oct 2024 01:54:05 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Dan Williams <dan.j.williams@...el.com>, <kevin.tian@...el.com>,
	<will@...nel.org>, <joro@...tes.org>, <suravee.suthikulpanit@....com>,
	<robin.murphy@....com>, <dwmw2@...radead.org>, <baolu.lu@...ux.intel.com>,
	<shuah@...nel.org>, <linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>,
	<linux-arm-kernel@...ts.infradead.org>, <linux-kselftest@...r.kernel.org>,
	<eric.auger@...hat.com>, <jean-philippe@...aro.org>, <mdf@...nel.org>,
	<mshavit@...gle.com>, <shameerali.kolothum.thodi@...wei.com>,
	<smostafa@...gle.com>, <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 06/19] iommufd/viommu: Add
 IOMMU_VIOMMU_SET/UNSET_VDEV_ID ioctl

On Thu, Sep 05, 2024 at 10:38:23AM -0700, Nicolin Chen wrote:
> On Thu, Sep 05, 2024 at 01:03:53PM -0300, Jason Gunthorpe wrote:
> > On Tue, Aug 27, 2024 at 09:59:43AM -0700, Nicolin Chen wrote:
> > > Introduce a pair of new ioctls to set/unset a per-viommu virtual device id
> > > that should be linked to a physical device id via an idev pointer.
> > 
> > Given some of the other discussions around CC I suspect we should
> > rename these to 'create/destroy virtual device' with an eye that
> > eventually they would be extended like other ops with per-CC platform
> > data.
> > 
> > ie this would be the interface to tell the CC trusted world that a
> > secure device is being added to a VM with some additional flags..
> > 
> > Right now it only conveys the vRID parameter of the virtual device
> > being created.
> >
> > A following question is if these objects should have their own IDs in
> > the iommufd space too, and then unset is not unset but just a normal
> > destroy object. If so then the thing you put in the ids xarray would
> > also just be a normal object struct.

I found that adding it as a new object makes things a lot of easier
since a vdevice can take refcounts of both viommu and idev. So both
destroy() callbacks wouldn't be bothered.

While confirming if I am missing something from the review comments,
I am not quite sure what is "the thing you put in the ids xarray"..
I only added a vRID xarray per viommu, yet that doesn't seem to be
able to merge into the normal object struct. Mind elaborating?

Thanks
Nicolin

> > This is probably worth doing if this is going to grow more CC stuff
> > later.
> 
> Having to admit that I have been struggling to find a better name
> than set_vdev_id, I also thought about something similar to that
> "create/destroy virtual device', yet was not that confident since
> we only have virtual device ID in its data structure. Also, the
> virtual device sounds a bit confusing, given we already have idev.
> 
> That being said, if we have a clear picture that in the long term
> we would extend it to hold more information, I think it could be
> a smart move.
> 
> Perhaps virtual device can have its own "attach" to vIOMMU? Or
> would you still prefer attaching via proxy hwpt_nested?
> 
> Thanks
> Nicolin