linux-kernel - [PATCH 5.9 01/14] selftests/powerpc: rfi_flush: disable entry flush if present

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Date:   Fri, 20 Nov 2020 12:03:39 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>, dja@...ens.net,
        Spoorthy S <spoorts2@...ibm.com>,
        Russell Currey <ruscur@...sell.cc>
Subject: [PATCH 5.9 01/14] selftests/powerpc: rfi_flush: disable entry flush if present

From: Russell Currey <ruscur@...sell.cc>

commit fcb48454c23c5679d1a2e252f127642e91b05cbe upstream.

We are about to add an entry flush. The rfi (exit) flush test measures
the number of L1D flushes over a syscall with the RFI flush enabled and
disabled. But if the entry flush is also enabled, the effect of enabling
and disabling the RFI flush is masked.

If there is a debugfs entry for the entry flush, disable it during the RFI
flush and restore it later.

Reported-by: Spoorthy S <spoorts2@...ibm.com>
Signed-off-by: Russell Currey <ruscur@...sell.cc>
Signed-off-by: Daniel Axtens <dja@...ens.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 tools/testing/selftests/powerpc/security/rfi_flush.c |   35 +++++++++++++++----
 1 file changed, 29 insertions(+), 6 deletions(-)

--- a/tools/testing/selftests/powerpc/security/rfi_flush.c
+++ b/tools/testing/selftests/powerpc/security/rfi_flush.c
@@ -50,16 +50,30 @@ int rfi_flush_test(void)
 	__u64 l1d_misses_total = 0;
 	unsigned long iterations = 100000, zero_size = 24 * 1024;
 	unsigned long l1d_misses_expected;
-	int rfi_flush_org, rfi_flush;
+	int rfi_flush_orig, rfi_flush;
+	int have_entry_flush, entry_flush_orig;
 
 	SKIP_IF(geteuid() != 0);
 
-	if (read_debugfs_file("powerpc/rfi_flush", &rfi_flush_org)) {
+	if (read_debugfs_file("powerpc/rfi_flush", &rfi_flush_orig) < 0) {
 		perror("Unable to read powerpc/rfi_flush debugfs file");
 		SKIP_IF(1);
 	}
 
-	rfi_flush = rfi_flush_org;
+	if (read_debugfs_file("powerpc/entry_flush", &entry_flush_orig) < 0) {
+		have_entry_flush = 0;
+	} else {
+		have_entry_flush = 1;
+
+		if (entry_flush_orig != 0) {
+			if (write_debugfs_file("powerpc/entry_flush", 0) < 0) {
+				perror("error writing to powerpc/entry_flush debugfs file");
+				return 1;
+			}
+		}
+	}
+
+	rfi_flush = rfi_flush_orig;
 
 	fd = perf_event_open_counter(PERF_TYPE_RAW, /* L1d miss */ 0x400f0, -1);
 	FAIL_IF(fd < 0);
@@ -68,6 +82,7 @@ int rfi_flush_test(void)
 
 	FAIL_IF(perf_event_enable(fd));
 
+	// disable L1 prefetching
 	set_dscr(1);
 
 	iter = repetitions;
@@ -109,8 +124,8 @@ again:
 		       repetitions * l1d_misses_expected / 2,
 		       passes, repetitions);
 
-	if (rfi_flush == rfi_flush_org) {
-		rfi_flush = !rfi_flush_org;
+	if (rfi_flush == rfi_flush_orig) {
+		rfi_flush = !rfi_flush_orig;
 		if (write_debugfs_file("powerpc/rfi_flush", rfi_flush) < 0) {
 			perror("error writing to powerpc/rfi_flush debugfs file");
 			return 1;
@@ -126,11 +141,19 @@ again:
 
 	set_dscr(0);
 
-	if (write_debugfs_file("powerpc/rfi_flush", rfi_flush_org) < 0) {
+	if (write_debugfs_file("powerpc/rfi_flush", rfi_flush_orig) < 0) {
 		perror("unable to restore original value of powerpc/rfi_flush debugfs file");
 		return 1;
 	}
 
+	if (have_entry_flush) {
+		if (write_debugfs_file("powerpc/entry_flush", entry_flush_orig) < 0) {
+			perror("unable to restore original value of powerpc/entry_flush "
+			       "debugfs file");
+			return 1;
+		}
+	}
+
 	return rc;
 }