Add a utility 'lsdexcr' to print the current DEXCR status. Useful for
quickly checking the status such as when debugging test failures or
verifying the new default DEXCR does what you want (for userspace at
least). Example output:

    # ./lsdexcr
       uDEXCR: 04000000 (NPHIE)
       HDEXCR: 00000000
    Effective: 04000000 (NPHIE)

            SBHE   (0): clear  	(Speculative branch hint enable)
          IBRTPD   (3): clear  	(Indirect branch recurrent target ...)
           SRAPD   (4): clear  	(Subroutine return address ...)
           NPHIE * (5): set  	(Non-privileged hash instruction enable)
            PHIE   (6): clear  	(Privileged hash instruction enable)

    DEXCR[NPHIE] enabled: hashst/hashchk working

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230616034846.311705-12-bgray@linux.ibm.com

Test the kernel DEXCR[NPHIE] interface and hashchk exception handling.

Introduces with it a DEXCR utils library for common DEXCR operations.

Volatile is used to prevent the compiler optimising away the signal
tests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230616034846.311705-11-bgray@linux.ibm.com

Adds _MSG assertion variants to provide more context behind why a
failure occurred. Also include unistd.h for _exit() and stdio.h for
fprintf(), and move ARRAY_SIZE macro to utils.h.

The _MSG variants and ARRAY_SIZE will be used by the following
DEXCR selftests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Reviewed-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230616034846.311705-10-bgray@linux.ibm.com

Reducing the time taken by dscr_sysfs_test.c allows restoring the
default timeout, which was removed in
commit 850507f30c38 ("selftests/powerpc: Turn off timeout setting for
benchmarks, dscr, signal, tm") because that test took too long.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-8-bgray@linux.ibm.com

This test case is extremely slow, taking around a minute compared to
most of the other DSCR tests taking a second at most. Perf shows most
time is spent by the kernel switching to each CPU it reads in
/sys/devices/system/cpu. This switching is an unavoidable consequnce
of reading all the .../cpuN/dscr values.

Remove the outer iteration loop from this test case, reducing the reads
from 1600 to 16. This still updates the DSCR 16 times and verifies on
every CPU each time, so I do not expect the lower coverage to be
meaningful. The speedup is significant: back down to ~1 second like the
other tests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-7-bgray@linux.ibm.com

The tests currently have a single writer thread updating the system
DSCR with a 1/1000 chance looped only 100 times. So only around one in
10 runs actually do anything.

* Add multiple threads to the dscr_explicit_random_test case.
* Use a barrier to make all the threads start work as simultaneously as
  possible.
* Use a rwlock and make all threads have a reasonable chance to write to
  the DSCR on each iteration.
  PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP is used to prevent
  writers from starving while all the other threads keep reading.
  Logging the reads/writes shows a decent mix across the whole test.
* Allow all threads a chance to write.
* Make the chance of writing more likely.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-6-bgray@linux.ibm.com

Add new cases to the relevant tests that use explicitly synchronized
threads to test the behaviour across context switches with less
randomness. By locking the participants to the same CPU we guarantee a
context switch occurs each time they make progress, which is a likely
failure point if the kernel is not tracking the thread local DSCR
correctly.

The random case is left in to keep exercising potential edge cases.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-5-bgray@linux.ibm.com

All current users of bind_to_cpu() don't care _which_ CPU they get, just
that they are bound to a single free one. So alter the interface to

	1. Accept a BIND_CPU_ANY value that tells it to automatically
	   pick a CPU
	2. Return the picked CPU

And convert all these users to bind_to_cpu(BIND_CPU_ANY).

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-4-bgray@linux.ibm.com

This function will be useful in the DSCR test patches later in this
series, so promote it to be shared by all powerpc selftests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-3-bgray@linux.ibm.com

Correct a couple of typos while working on other improvements to the
DSCR tests.

Signed-off-by: Benjamin Gray <bgray@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230406043320.125138-2-bgray@linux.ibm.com