RE: [PATCH rc 1/2] iommufd: Do not allow creating areas without READ or WRITE

From: Jason Gunthorpe <jgg@nvidia.com>
Sent: Thursday, August 22, 2024 10:46 PM

This results in passing 0 or just IOMMU_CACHE to iommu_map(). Most of
the page table formats don't like this:

  amdv1 - -EINVAL
  armv7s - returns 0, doesn't update mapped
  arm-lpae - returns 0 doesn't update mapped
  dart - returns 0, doesn't update mapped
  VT-D - returns -EINVAL

Unfortunately the three formats that return 0 cause serious problems:

 - Returning ret = but not uppdating mapped from domain->map_pages()
   causes an infinite loop in __iommu_map()

 - Not writing ioptes means that VFIO/iommufd have no way to recover them
   and we will have memory leaks and worse during unmap

Since almost nothing can support this, and it is a useless thing to do,
block it early in iommufd.

Cc: stable@kernel.org
Fixes: aad37e71d5c4 ("iommufd: IOCTLs for the io_pagetable")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Reviewed-by: Kevin Tian <kevin.tian@intel.com>