On Tue, Mar 27, 2018 at 2:48 PM, Michael Ellerman <mpe@xxxxxxxxxxxxxx> wrote: > Ram Pai <linuxram@xxxxxxxxxx> writes: > >> On Fri, Mar 16, 2018 at 10:02:22PM +1100, Balbir Singh wrote: >>> On Fri, Mar 16, 2018 at 9:33 PM, Ram Pai <linuxram@xxxxxxxxxx> wrote: >>> > Applications need the ability to associate an address-range with some >>> > key and latter revert to its initial default key. Pkey-0 comes close to >>> > providing this function but falls short, because the current >>> > implementation disallows applications to explicitly associate pkey-0 to >>> > the address range. >>> > >>> > Clarify the semantics of pkey-0 and provide the corresponding >>> > implementation. >>> > >>> > Pkey-0 is special with the following semantics. >>> > (a) it is implicitly allocated and can never be freed. It always exists. >>> > (b) it is the default key assigned to any address-range. >>> > (c) it can be explicitly associated with any address-range. >>> > >>> > Tested on powerpc only. Could not test on x86. >>> >>> Ram, >>> >>> I was wondering if we should check the AMOR values on the ppc side to make sure >>> that pkey0 is indeed available for use as default. I am still of the >>> opinion that we >> >> AMOR cannot be read/written by the OS in priviledge-non-hypervisor-mode. >> We could try testing if key-0 is available to the OS by temproarily >> changing the bits key-0 bits of AMR or IAMR register. But will be >> dangeorous to do, for you might disable read,execute of all the pages, >> since all pages are asscoiated with key-0 bydefault. > > No we should do what firmware tells us. If it says key 0 is available we > use it, otherwise we don't. > > Now if you notice the way the firmware API (device tree property) is > defined, it tells us how many keys are available, counting from 0. > I could not find counting from 0 anywhere, are we expected to look at the AMOR and figure out what we have access to? Why do we assume they'll be contiguous, it makes our life easy, but I really could not find any documentation on it > So for pkey 0 to be reserved there must be 0 keys available. > > End of story. > > cheers Cheers, Balbir Singh.
