On Tue, Dec 19, 2017 at 09:50:24PM +1100, Michael Ellerman wrote: > Dave Hansen <dave.hansen@xxxxxxxxx> writes: > > > On 11/06/2017 12:57 AM, Ram Pai wrote: > >> Expose useful information for programs using memory protection keys. > >> Provide implementation for powerpc and x86. > >> > >> On a powerpc system with pkeys support, here is what is shown: > >> > >> $ head /sys/kernel/mm/protection_keys/* > >> ==> /sys/kernel/mm/protection_keys/disable_access_supported <== > >> true > > > > This is cute, but I don't think it should be part of the ABI. Put it in > > debugfs if you want it for cute tests. The stuff that this tells you > > can and should come from pkey_alloc() for the ABI. > > Yeah I agree this is not sysfs material. > > In particular the total/usable numbers are completely useless vs other > threads allocating pkeys out from under you. The usable number is the minimum number of keys available for use by the application, not the number of keys **currently** available. Its a static number. I am dropping this patch. We can revisit this when a clear request for such a feature emerges. > > > > >> Any application wanting to use protection keys needs to be able to > >> function without them. They might be unavailable because the > >> hardware that the application runs on does not support them, the > >> kernel code does not contain support, the kernel support has been > >> disabled, or because the keys have all been allocated, perhaps by a > >> library the application is using. It is recommended that > >> applications wanting to use protection keys should simply call > >> pkey_alloc(2) and test whether the call succeeds, instead of > >> attempting to detect support for the feature in any other way. > > > > Do you really not have standard way on ppc to say whether hardware > > features are supported by the kernel? For instance, how do you know if > > a given set of registers are known to and are being context-switched by > > the kernel? > > Yes we do, we emit feature bits in the AT_HWCAP entry of the aux vector, > same as some other architectures. Ah. I was not aware of this. Thanks, RP -- 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>
