On Fri, Jun 24, 2022 at 10:56:15AM -0300, Jason Gunthorpe wrote: > > How about the updated commit log below? Thanks. > > > > The pinned PFN list returned from vfio_pin_pages() is converted using > > page_to_pfn(), so direct access via memcpy() will crash on S390 if the > > PFN is an IO PFN, as we have to use the memcpy_to/fromio(), which uses > > the special s390 IO access instructions. > > > > As a standard practice for security purpose, add kmap_local_page() to > > block any IO memory from ever getting into this call path. > > The kmap_local_page is not about the IO memory, the switch to struct > page is what is protecting against IO memory. > > Use kmap_local_page() is just the correct way to convert a struct page > into a CPU address to use with memcpy and it is a NOP on S390 because > it doesn't use highmem/etc. I thought the whole purpose of switching to "struct page *" was to use kmap_local_page() for the memcpy call, and the combination of these two does the protection. Do you mind explaining how the switching part does the protection? Thanks!
