linux-kernel - RE: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

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Date: Fri, 5 Jan 2024 02:16:31 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Jason Gunthorpe <jgg@...dia.com>, "Liu, Yi L" <yi.l.liu@...el.com>
CC: "joro@...tes.org" <joro@...tes.org>, "alex.williamson@...hat.com"
	<alex.williamson@...hat.com>, "robin.murphy@....com" <robin.murphy@....com>,
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>, "cohuck@...hat.com"
	<cohuck@...hat.com>, "eric.auger@...hat.com" <eric.auger@...hat.com>,
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	<kvm@...r.kernel.org>, "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
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	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
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	"linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>, "Duan,
 Zhenzhong" <zhenzhong.duan@...el.com>, "joao.m.martins@...cle.com"
	<joao.m.martins@...cle.com>, "Zeng, Xin" <xin.zeng@...el.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
Subject: RE: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d stage-1
 cache invalidation

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Thursday, January 4, 2024 10:37 PM
> 
> On Thu, Dec 14, 2023 at 07:26:39PM +0800, Yi Liu wrote:
> > Per the prior discussion[1], we agreed to move the error reporting into the
> > driver specific part. On Intel side, we want to report two devTLB
> > invalidation errors: ICE (invalid completion error) and ITE (invalidation
> > timeout error). Such errors have an additional SID information to tell
> > which device failed the devTLB invalidation. I've got the below structure.
> 
> IMHO all of this complexity is a consequence of the decision to hide
> the devtlb invalidation from the VM..
> 
> On the other hand I guess you want to do this because of the SIOV
> troubles where the vPCI function in the VM is entirely virtual and
> can't be trivially mapped to a real PCI function for ATC invalidation
> like ARM and AMD can do (but they also can't support SIOV because of
> this). :(
> 
> However it also makes it very confusing about how the VM would
> perceive an error - eg if it invalidates an SIOV device single PASID
> and that devtlb fails then the error should be connected back to the
> vPCI function for the SIOV's specific PASID and not back to the
> physical PCI function for the SIOV owner.
> 
> As the iommu driver itself has no idea about the vPCI functions this
> seems like it is going to get really confusing. The API I suggested in
> the other email is not entirely going to work as the vPCI function for
> SIOV cases will have to be identified by the (struct device, PASID) -
> while it would be easy enough for the iommu driver to provide the
> PASID, I'm not sure how the iommufd core will relate the PASID back to
> the iommu_device to understand SIOV without actually being aware of
> SIOV to some degree :\

we plan to add such awareness with a new binding helper:

https://lore.kernel.org/lkml/20231009085123.463179-4-yi.l.liu@intel.com/

and with metadata to track association between PASID's and iommufd vdev.

but in reality the relation could be identified in an easy way due to a SIOV
restriction which we discussed before - shared PASID space of PF disallows
assigning sibling vdev's to a same VM (otherwise no way to identify which
sibling vdev triggering an iopf when a pasid is used on both vdev's). That
restriction implies that within an iommufd context every iommufd_device
object should contain a unique struct device pointer. So PASID can be
instead ignored in the lookup then just always do iommufd_get_dev_id()
using struct device.