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Date:   Wed, 9 Aug 2023 12:12:25 -0700
From:   Nicolin Chen <nicolinc@nvidia.com>
To:     Jason Gunthorpe <jgg@nvidia.com>
CC:     "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 01:24:56PM -0300, Jason Gunthorpe wrote:
> 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));

OK. So, IIUIC, the opaque should be:

struct iommu_user_data {
	void __user *data_uptr;
	size_t data_len;
}user_data;

And core does basic sanity of data_uptr != NULL and data_len !=0
before passing this to driver, and then do a full sanity during
the iommufd_get_args (or iommufd_get_user_data?) call.

> 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.

OK. I will rework this part today.

> Similarly for managing the array of invalidation commands.

You mean an embedded uptr inside a driver user data struct right?
Sure, that should go through the new helper too.

Thanks
Nicolin