On Mon, Dec 18, 2017 at 02:28:14PM -0800, Dave Hansen wrote: > On 12/18/2017 02:18 PM, Ram Pai wrote: > > b) minimum number of keys available to the application. > > if libraries consumes a few, they could provide a library > > interface to the application informing the number available to > > the application. The library interface can leverage (b) to > > provide the information. > > OK, let's see a real user of this including a few libraries. Then we'll > put it in the kernel. > > > c) types of disable-rights supported by keys. > > Helps the application to determine the types of disable-features > > available. This is helpful, otherwise the app has to > > make pkey_alloc() call with the corresponding parameter set > > and see if it suceeds or fails. Painful from an application > > point of view, in my opinion. > > Again, let's see a real-world use of this. How does it look? How does > an app "fall back" if it can't set a restriction the way it wants to? > > Are we *sure* that such an interface makes sense? For instance, will it > be possible for some keys to be execute-disable while other are only > write-disable? Can it be on x86? its not possible on ppc. the keys can *all* be the-same-attributes-disable all the time. However you are right. Its conceivable that some arch could provide a feature where it can be x-attribute-disable for key 'a' and y-attribute-disable for key 'b'. But than its a bit of a headache for an application to consume such a feature. Ben: I recall you requesting this feature. Thoughts? > > > 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. RP -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
