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

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Date: Wed, 3 Jan 2024 12:18:35 -0800
From: Nicolin Chen <nicolinc@...dia.com>
To: Jason Gunthorpe <jgg@...dia.com>
CC: Yi Liu <yi.l.liu@...el.com>, "Tian, Kevin" <kevin.tian@...el.com>,
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	<yan.y.zhao@...el.com>
Subject: Re: [PATCH v7 1/3] iommufd: Add data structure for Intel VT-d
 stage-1 cache invalidation

On Wed, Jan 03, 2024 at 01:52:02PM -0400, Jason Gunthorpe wrote:
> On Wed, Jan 03, 2024 at 09:06:23AM -0800, Nicolin Chen wrote:
> > On Wed, Jan 03, 2024 at 12:58:48PM -0400, Jason Gunthorpe wrote:
> > > On Wed, Jan 03, 2024 at 08:48:46AM -0800, Nicolin Chen wrote:
> > > > > You can pass the ctx to the invalidate op, it is already implied
> > > > > because the passed iommu_domain is linked to a single iommufd ctx.
> > > > 
> > > > The device virtual id lookup API needs something similar, yet it
> > > > likely needs a viommu pointer (or its id) instead? As the table
> > > > is attached to a viommu while an ictx can have multiple viommus,
> > > > right?
> > > 
> > > Yes, when we get to an API for that it will have to be some op
> > > 'invalidate_viommu(..)' and it can get the necessary pointers.
> > 
> > OK! I will try that first.
> > 
> > > The viommu object will have to be some driver object like the
> > > iommu_domain.
> > 
> > I drafted something like this, linking it to struct iommu_device:
> > 
> > +struct iommufd_viommu {
> > +       struct iommufd_object obj;
> > +       struct iommufd_ctx *ictx;
> > +       struct iommu_device *iommu_dev;
> > +       struct iommufd_hwpt_paging *hwpt;
> > +       /* array of struct iommufd_device, indexed by device virtual id */
> > +       struct xarray device_ids;
> > +};
> 
> The driver would have to create it and there would be some driver
> specific enclosing struct to go with it
> 
> Perhaps device_ids goes in the driver specific struct, I don't know.

+struct iommufd_viommu {
+	struct iommufd_object obj;
+	struct iommufd_ctx *ictx;
+	struct iommu_device *iommu_dev;
+	struct iommufd_hwpt_paging *hwpt;	/* maybe unneeded */
+
+	int vmid;
+
+	union iommu_driver_user_data {
+		struct iommu_driver_user_vtd;
+		struct iommu_driver_user_arm_smmuv3;
+		struct iommu_driver_user_amd_viommu;
+	};
+};

Then iommu_ops would need something like:
	iommu_user_alloc/free(struct iommu_device *iommu_dev,
			      union *iommu_driver_user_data, int *vmid);
	iommu_user_set/unset_dev_id(union iommu_driver_user_data,
				    struct device* dev. u32/u64 id);
	iommu_user_invalidate(union iommu_driver_user_data *iommu,
			      struct iommu_user_data_array *array);

Comments and ideas on better naming convention?

> Not sure it should have hwpt at all, probably vmid should come from
> the driver specific struct in some driver specific way

The idea having a hwpt pointer is to share the paging hwpt among
the viommu objects. I don't think it "shouldn't have", yet likely
we can avoid it depending on whether it will have some use or not
in the context.

Nicolin