On Tue, Dec 19, 2017 at 09:31:22AM +0100, Gabriel Paubert wrote: > On Mon, Dec 18, 2017 at 03:15:51PM -0800, Ram Pai wrote: > > On Mon, Dec 18, 2017 at 02:28:14PM -0800, Dave Hansen wrote: > > > On 12/18/2017 02:18 PM, Ram Pai wrote: > > > ....snip... > > > > I think on x86 you look for some hardware registers to determine > > > > which hardware features are enabled by the kernel. > > > > > > No, we use CPUID. It's a part of the ISA that's designed for > > > enumerating CPU and (sometimes) OS support for CPU features. > > > > > > > We do not have generic support for something like that on ppc. The > > > > kernel looks at the device tree to determine what hardware features > > > > are available. But does not have mechanism to tell the hardware to > > > > track which of its features are currently enabled/used by the > > > > kernel; atleast not for the memory-key feature. > > > > > > Bummer. You're missing out. > > > > > > But, you could still do this with a syscall. "Hey, kernel, do you > > > support this feature?" > > > > or do powerpc specific sysfs interface. > > or a debugfs interface. > > getauxval(3) ? > > With AT_HWCAP or HWCAP2 as parameter already gives information about > features supported by the hardware and the kernel. > > Taking one bit to expose the availability of protection keys to > applications does not look impossible. > > Do I miss something obvious? No. I am told this is possible aswell. RP
