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

[Liu, Yi L]

> From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> Sent: Friday, August 4, 2023 10:04 PM
> 
> 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

Yes.

> 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;

Sure. The way in patch 09 is a bit tricky. The above is better and clearer. 😊

> 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..

Yes. should fail. It should be failed in copy_struct_from_user() as I use
it to copy the struct iommu_hwpt_vtd_s1_invalidate_desc.

* -E2BIG:  (@usize > @ksize) and there are non-zero trailing bytes in @src.

Regards,
Yi Liu