On Tue, Jul 05, 2022 at 11:27:58PM -0700, Nicolin Chen wrote: > A PFN is not secure enough to promise that the memory is not IO. And > direct access via memcpy() that only handles CPU memory will crash on > S390 if the PFN is an IO PFN, as we have to use the memcpy_to/fromio() > that uses the special S390 IO access instructions. On the other hand, > a "struct page *" is always a CPU coherent thing that fits memcpy(). > > Also, casting a PFN to "void *" for memcpy() is not a proper practice, > kmap_local_page() is the correct API to call here, though S390 doesn't > use highmem, which means kmap_local_page() is a NOP. > > There's a following patch changing the vfio_pin_pages() API to return > a list of "struct page *" instead of PFNs. It will block any IO memory > from ever getting into this call path, for such a security purpose. In > this patch, add kmap_local_page() to prepare for that. > > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx> > Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx> > --- > drivers/s390/cio/vfio_ccw_cp.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Jason
