powerpc/64s: Improve RFI L1-D cache flush fallback

BugLink: https://bugs.launchpad.net/bugs/1830176

commit bdcb1aef upstream.

The fallback RFI flush is used when firmware does not provide a way
to flush the cache. It's a "displacement flush" that evicts useful
data by displacing it with an uninteresting buffer.

The flush has to take care to work with implementation specific cache
replacment policies, so the recipe has been in flux. The initial
slow but conservative approach is to touch all lines of a congruence
class, with dependencies between each load. It has since been
determined that a linear pattern of loads without dependencies is
sufficient, and is significantly faster.

Measuring the speed of a null syscall with RFI fallback flush enabled
gives the relative improvement:

P8 - 1.83x
P9 - 1.75x

The flush also becomes simpler and more adaptable to different cache
geometries.
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[juergh: Adjusted context.]
Signed-off-by: Juerg Haefliger <juergh@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/powerpc/xmon/xmon.c

@@ -2151,8 +2151,6 @@ static void dump_one_paca(int cpu)
 		printf(" slb_cache[%d]:        = 0x%016lx\n", i, p->slb_cache[i]);
 
 	DUMP(p, rfi_flush_fallback_area, "px");
-	DUMP(p, l1d_flush_congruence, "llx");
-	DUMP(p, l1d_flush_sets, "llx");
 #endif
 	DUMP(p, dscr_default, "llx");
 #ifdef CONFIG_PPC_BOOK3E