selftests/powerpc: Skip PROT_SAO test in guests/LPARS

In commit 9b725a90 ("powerpc/64s: Disallow PROT_SAO in LPARs by
default") PROT_SAO was disabled in guests/LPARs by default. So skip
the test if we are running in a guest to avoid a spurious failure.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200901124653.523182-1-mpe@ellerman.id.au

tools/testing/selftests/powerpc/mm/prot_sao.c

@@ -7,6 +7,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <sys/mman.h>
+#include <unistd.h>
 
 #include <asm/cputable.h>
 
@@ -18,9 +19,13 @@ int test_prot_sao(void)
 {
 	char *p;
 
-	/* SAO was introduced in 2.06 and removed in 3.1 */
+	/*
+	 * SAO was introduced in 2.06 and removed in 3.1. It's disabled in
+	 * guests/LPARs by default, so also skip if we are running in a guest.
+	 */
 	SKIP_IF(!have_hwcap(PPC_FEATURE_ARCH_2_06) ||
-		have_hwcap2(PPC_FEATURE2_ARCH_3_1));
+		have_hwcap2(PPC_FEATURE2_ARCH_3_1) ||
+		access("/proc/device-tree/rtas/ibm,hypertas-functions", F_OK) == 0);
 
 	/*
 	 * Ensure we can ask for PROT_SAO.