On 07/07/2016 07:45 AM, Mel Gorman wrote: > On Thu, Jul 07, 2016 at 05:47:28AM -0700, Dave Hansen wrote: >> > >> > From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> >> > >> > This establishes two more system calls for protection key management: >> > >> > unsigned long pkey_get(int pkey); >> > int pkey_set(int pkey, unsigned long access_rights); >> > >> > The return value from pkey_get() and the 'access_rights' passed >> > to pkey_set() are the same format: a bitmask containing >> > PKEY_DENY_WRITE and/or PKEY_DENY_ACCESS, or nothing set at all. >> > >> > These can replace userspace's direct use of the new rdpkru/wrpkru >> > instructions. ... > This one feels like something that can or should be implemented in > glibc. I generally agree, except that glibc doesn't have any visibility into whether a pkey is currently valid or not. > There is no real enforcement of the values yet looking them up or > setting them takes mmap_sem for write. There are checks for mm_pkey_is_allocated(). That's the main thing these syscalls add on top of the raw instructions. > Applications that frequently get > called will get hammed into the ground with serialisation on mmap_sem > not to mention the cost of the syscall entry/exit. I think we can do both of them without mmap_sem, as long as we resign ourselves to this just being fundamentally racy (which it is already, I think). But, is it worth performance-tuning things that we don't expect performance-sensitive apps to be using in the first place? They'll just use the RDPKRU/WRPKRU instructions directly. Ingo, do you still feel strongly that these syscalls (pkey_set/get()) should be included? Of the 5, they're definitely the two with the weakest justification. -- 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>