Re: [PATCH v4 07/12] iommufd: Add data structure for Intel VT-d stage-1 cache invalidation

[Jason Gunthorpe]

On Fri, Aug 04, 2023 at 01:04:57PM +0000, Liu, Yi L wrote:
> > > Having the driver copy in a loop might be better
> > >
> > 
> > Can you elaborate?
> 
> I think Jason means the way in patch 09.

Yeah, you can't reuse the stack buffer for an array, so patch 9 copies
each element uniquely.

This is more calls to copy_to_user, which has some cost

But we avoid a memory allocation

Patch 9 should not abuse the user_data, cast it to the inv_info and
just put req on the stack:

	struct iommu_hwpt_vtd_s1_invalidate *inv_info = user_data;
	struct iommu_hwpt_vtd_s1_invalidate_desc req;

But I'm not sure about this entry_size logic, what happens if the
entry_size is larger than the kernel supports? I think it should
fail..

Jason