Dave Hansen <dave.hansen@xxxxxxxxx> writes: > On 7/23/20 10:08 AM, Andy Lutomirski wrote: >> Suppose some kernel code (a syscall or kernel thread) changes PKRS >> then takes a page fault. The page fault handler needs a fresh PKRS. >> Then the page fault handler (say a VMA’s .fault handler) changes >> PKRS. The we get an interrupt. The interrupt *also* needs a fresh >> PKRS and the page fault value needs to be saved somewhere. >> >> So we have more than one saved value per thread, and thread_struct >> isn’t going to solve this problem. > > Taking a step back... This is all true only if we decide that we want > protection keys to provide protection during exceptions and interrupts. > Right now, the code supports nesting: > > kmap(foo); > kmap(bar); > kunmap(bar); > kunmap(foo); > > with a reference count. So, the nested kmap() will see the count > elevated and do nothing. Hopefully with a big fat warning if the nested map requires a different key than the outer one.
