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Date:   Wed, 9 Aug 2023 13:24:56 -0300
From:   Jason Gunthorpe <jgg@nvidia.com>
To:     "Liu, Yi L" <yi.l.liu@intel.com>
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Subject: Re: [PATCH v4 09/12] iommu/vt-d: Add iotlb flush for nested domain
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On Wed, Aug 09, 2023 at 09:30:12AM +0000, Liu, Yi L wrote:

> Yeah, adding new structures to ucmd_buffer may increase the size as
> well if the new one is larger. While for an array, if there is new entry,
> it is for sure to increase the size. I remember there is one tricky thing
> when handling the selftest type. E.g. it is defined as 0xbadbeef, if using
> it to index array, it would expire. So we have some special handling on
> it. If defining the things in iommu_ops, it is simpler. Selftest may be
> not so critical to determining the direction though.

Maybe we are trying too hard to make it "easy" on the driver.

Can't we just have the driver invoke some:

driver_iommufd_invalidate_op(??? *opaque)
{
	struct driver_base_struct args;

        rc = iommufd_get_args(opaque, &args, sizeof(args),
	     offsetof(args, last));
	if (rc)
	   return rc;
}

The whole point of this excercise was to avoid the mistake where
drivers code the uapi checks incorrectly. We can achieve the same
outcome by providing a mandatory helper.

Similarly for managing the array of invalidation commands.

Jason