Re: [PATCH 03/25] powerpc: track allocation status of all pkeys

On Mon, Oct 23, 2017 at 03:11:28PM +0530, Aneesh Kumar K.V wrote:

Ram Pai [off-list ref] writes:

quoted

Total 32 keys are available on power7 and above. However
pkey 0,1 are reserved. So effectively we  have  30 pkeys.

When you say reserved, reserved by whom? Is that part of ISA or PAPR ?
Also do you expect that to change. If not why all these indirection?
Can we have the mask as a #define for 4K and 64K page size
config?

The reserved keys cannot be determined
statically. It depends on the platform and the key info exported to us
by the device-tree.  Hence it cannot be macro'd.

One of the subsequent patch, reads the device tree and sets pkeys_total
appropriately. FYI.

BTW: key 0 is reserved by the ISA.  key 1 is reserved, but its nebulous.
There is a programming note in the ISA to avoid key 1. Also testing
and experimentation with key 1 lead to unpredicatable behavior on
powervm. Key 31 may or may not be used by the hypervisor. The device
tree has to be referred to determine that.

Bottomline, the mask can be determined only during runtime.

RP