[PATCH 22/24] drm/amdkfd: Adding new IOCTL for scratch memory v2

[Jerome Glisse]

On Tue, Aug 15, 2017 at 11:00:20PM -0400, Felix Kuehling wrote:
> From: Moses Reuben <moses.reuben at amd.com>
> 
> v2:
> * Renamed ALLOC_MEMORY_OF_SCRATCH to SET_SCRATCH_BACKING_VA
> * Removed size parameter from the ioctl, it was unused
> * Removed hole in ioctl number space
> * No more call to write_config_static_mem
> * Return correct error code from ioctl

What kind of memory is suppose to back this virtual address
range ? How big is the range suppose to be ? Can it be any
valid virtual address ?

My worry here is to ascertain that one can not abuse this
ioctl say to set the virtual address to some mmaped shared
library code/data section and write something malicious
there.

I am assuming that if it has to go through ATS/PASID of the
IOMMUv2 then the write protection will be asserted and we
will see proper COW (copy on write) due to mmap PRIVATE flags.


Idealy this area should be a special vma and the driver
should track its lifetime and cancel GPU jobs if it is
unmap. But i am unsure on how dynamic is that scratch
memory suppose to be (ie do you allocate new scratch memory
with every GPU job or is it allocated once and reuse for
every jobs).

Bigger commit message would be nice too. Like i had tons
of i believe valid questions.

Cheers,
Jérôme