IBM AIX Continuous Availability Features - IBM Redbooks

added a protection gate for the interface) and the hardware keyset established by module
configuration. Future calls to a configuration entry point can execute an explicit protection
gate, but this requires logic in the module configuration point to differentiate the first and
subsequent calls.
When a new (key-safe) thread/k-proc is created, it starts execution at an initialization function
passed to kthread_start()/initp(). For key-safe extensions, the kernel calls this entry point with
a keyset that contains only the KKEY_PUBLIC kernel key. The k-thread/k-proc initialization
function is an entry point, so it is the callee’s responsibility to add a protection gate if another
keyset is required.
In these two cases, the kernel is required to load the legacy keyset before calling an
initialization function contained in a key-unsafe extension.
Multiple page sizes
Significant work has been done to exploit medium (64 K) and large (16 M) pages in the
kernel. Medium pages continue to be usable with kernel keys. Kernel heaps can continue to
be backed by medium-size pages when kernel keys are enabled. There will be a heap per
hardware key, and that will increase the kernel’s working set. Code setting storage keys on all
kernel memory must be aware of the page size.
3.7.6 Example using kernel keys
This example tries to load a kernel extension that has the ability to use kernel protection keys.
It will provide a system call kkey_test() that will be called by user program myprog.c (shown in
Example 3-24 on page 93). The make file for this program is shown in Example 3-21.
Note: The kernel must be built using bosboot -aD to include the kernel debugger. Without
this, you will not see the kernel printfs, and the dsi will not pop you into kdb, but will just
take a dump.
When system call kkey_test() is called with parameter=0, it tries to access private heap with
KKEY_VMM in its protection gate (as shown in Example 3-28 on page 96).
When system call kkey_test() is called with parameter>0, it tries to access private heap
without KKEY_VMM in its protection gate (as shown in Example 3-29 on page 96).
Example 3-21 Make file for kernel key example
CC=/usr/vac/bin/cc
LD=/usr/bin/ld
LIB= -bI:kkey_set.exp
UTIL=.
all: myprog service kkey_set64
kkey_set64: kkey_set.c kkey_set.exp
$(CC) -q64 -D_KERNEL -D_KERNSYS -D_64BIT_KERNEL -D__64BIT__ -o kkey_set64.o -c
kkey_set.c
$(LD) -b64 -o kkey_set64 kkey_set64.o -e kkey_test_init -bE:kkey_set.exp
-bI:/usr/lib/kernex.exp -lcsys
service: service.c
$(CC) -o service service.c
90 IBM AIX Continuous Availability Features