selftests/powerpc/dexcr: Add DEXCR status utility lsdexcr

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

tools/testing/selftests/powerpc/dexcr/.gitignore

@@ -1 +1,2 @@
 hashchk_test
+lsdexcr

tools/testing/selftests/powerpc/dexcr/Makefile

@@ -1,7 +1,9 @@
 TEST_GEN_PROGS := hashchk_test
+TEST_GEN_FILES := lsdexcr
 
 include ../../lib.mk
 
 $(OUTPUT)/hashchk_test: CFLAGS += -fno-pie $(call cc-option,-mno-rop-protect)
 
 $(TEST_GEN_PROGS): ../harness.c ../utils.c ./dexcr.c
+$(TEST_GEN_FILES): ../utils.c ./dexcr.c

tools/testing/selftests/powerpc/dexcr/lsdexcr.c

@@ -0,0 +1,141 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+#include "dexcr.h"
+#include "utils.h"
+
+static unsigned int dexcr;
+static unsigned int hdexcr;
+static unsigned int effective;
+
+struct dexcr_aspect {
+	const char *name;
+	const char *desc;
+	unsigned int index;
+};
+
+static const struct dexcr_aspect aspects[] = {
+	{
+		.name = "SBHE",
+		.desc = "Speculative branch hint enable",
+		.index = 0,
+	},
+	{
+		.name = "IBRTPD",
+		.desc = "Indirect branch recurrent target prediction disable",
+		.index = 3,
+	},
+	{
+		.name = "SRAPD",
+		.desc = "Subroutine return address prediction disable",
+		.index = 4,
+	},
+	{
+		.name = "NPHIE",
+		.desc = "Non-privileged hash instruction enable",
+		.index = 5,
+	},
+	{
+		.name = "PHIE",
+		.desc = "Privileged hash instruction enable",
+		.index = 6,
+	},
+};
+
+static void print_list(const char *list[], size_t len)
+{
+	for (size_t i = 0; i < len; i++) {
+		printf("%s", list[i]);
+		if (i + 1 < len)
+			printf(", ");
+	}
+}
+
+static void print_dexcr(char *name, unsigned int bits)
+{
+	const char *enabled_aspects[ARRAY_SIZE(aspects) + 1] = {NULL};
+	size_t j = 0;
+
+	printf("%s: %08x", name, bits);
+
+	if (bits == 0) {
+		printf("\n");
+		return;
+	}
+
+	for (size_t i = 0; i < ARRAY_SIZE(aspects); i++) {
+		unsigned int mask = DEXCR_PR_BIT(aspects[i].index);
+
+		if (bits & mask) {
+			enabled_aspects[j++] = aspects[i].name;
+			bits &= ~mask;
+		}
+	}
+
+	if (bits)
+		enabled_aspects[j++] = "unknown";
+
+	printf(" (");
+	print_list(enabled_aspects, j);
+	printf(")\n");
+}
+
+static void print_aspect(const struct dexcr_aspect *aspect)
+{
+	const char *attributes[8] = {NULL};
+	size_t j = 0;
+	unsigned long mask;
+
+	mask = DEXCR_PR_BIT(aspect->index);
+	if (dexcr & mask)
+		attributes[j++] = "set";
+	if (hdexcr & mask)
+		attributes[j++] = "set (hypervisor)";
+	if (!(effective & mask))
+		attributes[j++] = "clear";
+
+	printf("%12s %c (%d): ", aspect->name, effective & mask ? '*' : ' ', aspect->index);
+	print_list(attributes, j);
+	printf("  \t(%s)\n", aspect->desc);
+}
+
+int main(int argc, char *argv[])
+{
+	if (!dexcr_exists()) {
+		printf("DEXCR not detected on this hardware\n");
+		return 1;
+	}
+
+	dexcr = get_dexcr(DEXCR);
+	hdexcr = get_dexcr(HDEXCR);
+	effective = dexcr | hdexcr;
+
+	print_dexcr("    DEXCR", dexcr);
+	print_dexcr("   HDEXCR", hdexcr);
+	print_dexcr("Effective", effective);
+	printf("\n");
+
+	for (size_t i = 0; i < ARRAY_SIZE(aspects); i++)
+		print_aspect(&aspects[i]);
+	printf("\n");
+
+	if (effective & DEXCR_PR_NPHIE) {
+		printf("DEXCR[NPHIE] enabled: hashst/hashchk ");
+		if (hashchk_triggers())
+			printf("working\n");
+		else
+			printf("failed to trigger\n");
+	} else {
+		printf("DEXCR[NPHIE] disabled: hashst/hashchk ");
+		if (hashchk_triggers())
+			printf("unexpectedly triggered\n");
+		else
+			printf("ignored\n");
+	}
+
+	return 0;
+}