On 10/21/2015 11:55 AM, Andy Lutomirski wrote: > On Fri, Oct 16, 2015 at 8:12 AM, Dave Hansen <dave@xxxxxxxx> wrote: >> On 10/03/2015 12:27 AM, Ingo Molnar wrote: >>> - Along similar considerations, also add a sys_pkey_query() system call to query >>> the mapping of a specific pkey. (returns -EBADF or so if the key is not mapped >>> at the moment.) This too could be vDSO accelerated in the future. >>> >>> I.e. something like: >>> >>> unsigned long sys_pkey_alloc (unsigned long flags, unsigned long init_val) >>> unsigned long sys_pkey_set (int pkey, unsigned long new_val) >>> unsigned long sys_pkey_get (int pkey) >>> unsigned long sys_pkey_free (int pkey) >> >> The pkey_set() operation is going to get a wee bit interesting with signals. >> >> pkey_set() will modify the _current_ context's PKRU which includes the >> register itself and the kernel XSAVE buffer (if active). But, since the >> PKRU state is saved/restored with the XSAVE state, we will blow away any >> state set during the signal. >> >> I _think_ the right move here is to either keep a 'shadow' version of >> PKRU inside the kernel (for each thread) and always update the task's >> XSAVE PKRU state when returning from a signal handler. Or, _copy_ the >> signal's PKRU state in to the main process's PKRU state when returning >> from a signal. > > Ick. Or we could just declare that signals don't affect the PKRU > state by default and mask it off in sigreturn. Yeah, I've been messing with it in a few forms and it's pretty ugly. I think it will be easier if we say the PKRU rights are not inherited by signals and changes during a signal are tossed out. Signal handlers are special anyway and folks have to be careful writing them. > In fact, maybe we should add a general xfeature (or whatever it's > called these days) to the xstate in the signal context that controls > which pieces are restored. Then user code can tweak it if needed in > signal handlers. Yeah, that's probably a good idea long-term. We're only getting more and more things managed by XSAVE and it's going to be increasingly interesting to glue real semantics back on top. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>