Mshare is a developing feature proposed by Anthony Yznaga and Khalid Aziz
that enables sharing of PTEs across processes. The V3 patch set has been
posted for review:
https://lore.kernel.org/linux-mm/20250820010415.699353-1-anthony.yznaga@ora…
This patch set adds selftests to exercise and demonstrate basic
functionality of mshare.
The initial tests use open, ioctl, and mmap syscalls to establish a shared
memory mapping between two processes and verify the expected behavior.
Additional tests are included to check interoperability with swap and
Transparent Huge Pages.
Future work will extend coverage to other use cases such as integration
with KVM and more advanced scenarios.
This series is intended to be applied on top of mshare V3, which is
based on mm-new (2025-08-15).
Yongting Lin (8):
mshare: Add selftests
mshare: selftests: Adding config fragment
mshare: selftests: Add some helper function for mshare filesystem
mshare: selftests: Add test case shared memory
mshare: selftests: Add test case ioctl unmap
mshare: selftests: Add some helper functions for reading and
controlling cgroup
mshare: selftests: Add test case to demostrate the swaping of mshare
memory
mshare: selftests: Add test case to demostrate that mshare doesn't
support THP
tools/testing/selftests/mshare/.gitignore | 3 +
tools/testing/selftests/mshare/Makefile | 7 +
tools/testing/selftests/mshare/basic.c | 108 ++++++++++
tools/testing/selftests/mshare/config | 1 +
tools/testing/selftests/mshare/memory.c | 82 +++++++
tools/testing/selftests/mshare/util.c | 251 ++++++++++++++++++++++
6 files changed, 452 insertions(+)
create mode 100644 tools/testing/selftests/mshare/.gitignore
create mode 100644 tools/testing/selftests/mshare/Makefile
create mode 100644 tools/testing/selftests/mshare/basic.c
create mode 100644 tools/testing/selftests/mshare/config
create mode 100644 tools/testing/selftests/mshare/memory.c
create mode 100644 tools/testing/selftests/mshare/util.c
--
2.20.1
One fix for occasional failures I found while testing and a bunch of
cleanups that should make that test easier to digest.
Tested on x86-64, the test seems to reliably pass.
Cc: Andrew Morton <akpm(a)linux-foundation.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes(a)oracle.com>
Cc: Zi Yan <ziy(a)nvidia.com>
Cc: Baolin Wang <baolin.wang(a)linux.alibaba.com>
Cc: "Liam R. Howlett" <Liam.Howlett(a)oracle.com>
Cc: Nico Pache <npache(a)redhat.com>
Cc: Ryan Roberts <ryan.roberts(a)arm.com>
Cc: Dev Jain <dev.jain(a)arm.com>
Cc: Barry Song <baohua(a)kernel.org>
Cc: Wei Yang <richard.weiyang(a)gmail.com>
David Hildenbrand (2):
selftests/mm: split_huge_page_test: fix occasional
is_backed_by_folio() wrong results
selftests/mm: split_huge_page_test: cleanups for split_pte_mapped_thp
test
.../selftests/mm/split_huge_page_test.c | 138 ++++++++++--------
1 file changed, 81 insertions(+), 57 deletions(-)
base-commit: b73c6f2b5712809f5f386780ac46d1d78c31b2e6
--
2.50.1
The BTF dumper code currently displays arrays of characters as just that -
arrays, with each character formatted individually. Sometimes this is what
makes sense, but it's nice to be able to treat that array as a string.
This change adds a special case to the btf_dump functionality to allow
0-terminated arrays of single-byte integer values to be printed as
character strings. Characters for which isprint() returns false are
printed as hex-escaped values. This is enabled when the new ".emit_strings"
is set to 1 in the btf_dump_type_data_opts structure.
As an example, here's what it looks like to dump the string "hello" using
a few different field values for btf_dump_type_data_opts (.compact = 1):
- .emit_strings = 0, .skip_names = 0: (char[6])['h','e','l','l','o',]
- .emit_strings = 0, .skip_names = 1: ['h','e','l','l','o',]
- .emit_strings = 1, .skip_names = 0: (char[6])"hello"
- .emit_strings = 1, .skip_names = 1: "hello"
Here's the string "h\xff", dumped with .compact = 1 and .skip_names = 1:
- .emit_strings = 0: ['h',-1,]
- .emit_strings = 1: "h\xff"
Signed-off-by: Blake Jones <blakejones(a)google.com>
---
tools/lib/bpf/btf.h | 3 ++-
tools/lib/bpf/btf_dump.c | 55 +++++++++++++++++++++++++++++++++++++++-
2 files changed, 56 insertions(+), 2 deletions(-)
diff --git a/tools/lib/bpf/btf.h b/tools/lib/bpf/btf.h
index 4392451d634b..ccfd905f03df 100644
--- a/tools/lib/bpf/btf.h
+++ b/tools/lib/bpf/btf.h
@@ -326,9 +326,10 @@ struct btf_dump_type_data_opts {
bool compact; /* no newlines/indentation */
bool skip_names; /* skip member/type names */
bool emit_zeroes; /* show 0-valued fields */
+ bool emit_strings; /* print char arrays as strings */
size_t :0;
};
-#define btf_dump_type_data_opts__last_field emit_zeroes
+#define btf_dump_type_data_opts__last_field emit_strings
LIBBPF_API int
btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 460c3e57fadb..7c2f1f13f958 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -68,6 +68,7 @@ struct btf_dump_data {
bool compact;
bool skip_names;
bool emit_zeroes;
+ bool emit_strings;
__u8 indent_lvl; /* base indent level */
char indent_str[BTF_DATA_INDENT_STR_LEN];
/* below are used during iteration */
@@ -2028,6 +2029,52 @@ static int btf_dump_var_data(struct btf_dump *d,
return btf_dump_dump_type_data(d, NULL, t, type_id, data, 0, 0);
}
+static int btf_dump_string_data(struct btf_dump *d,
+ const struct btf_type *t,
+ __u32 id,
+ const void *data)
+{
+ const struct btf_array *array = btf_array(t);
+ const char *chars = data;
+ __u32 i;
+
+ /* Make sure it is a NUL-terminated string. */
+ for (i = 0; i < array->nelems; i++) {
+ if ((void *)(chars + i) >= d->typed_dump->data_end)
+ return -E2BIG;
+ if (chars[i] == '\0')
+ break;
+ }
+ if (i == array->nelems) {
+ /* The caller will print this as a regular array. */
+ return -EINVAL;
+ }
+
+ btf_dump_data_pfx(d);
+ btf_dump_printf(d, "\"");
+
+ for (i = 0; i < array->nelems; i++) {
+ char c = chars[i];
+
+ if (c == '\0') {
+ /*
+ * When printing character arrays as strings, NUL bytes
+ * are always treated as string terminators; they are
+ * never printed.
+ */
+ break;
+ }
+ if (isprint(c))
+ btf_dump_printf(d, "%c", c);
+ else
+ btf_dump_printf(d, "\\x%02x", (__u8)c);
+ }
+
+ btf_dump_printf(d, "\"");
+
+ return 0;
+}
+
static int btf_dump_array_data(struct btf_dump *d,
const struct btf_type *t,
__u32 id,
@@ -2055,8 +2102,13 @@ static int btf_dump_array_data(struct btf_dump *d,
* char arrays, so if size is 1 and element is
* printable as a char, we'll do that.
*/
- if (elem_size == 1)
+ if (elem_size == 1) {
+ if (d->typed_dump->emit_strings &&
+ btf_dump_string_data(d, t, id, data) == 0) {
+ return 0;
+ }
d->typed_dump->is_array_char = true;
+ }
}
/* note that we increment depth before calling btf_dump_print() below;
@@ -2544,6 +2596,7 @@ int btf_dump__dump_type_data(struct btf_dump *d, __u32 id,
d->typed_dump->compact = OPTS_GET(opts, compact, false);
d->typed_dump->skip_names = OPTS_GET(opts, skip_names, false);
d->typed_dump->emit_zeroes = OPTS_GET(opts, emit_zeroes, false);
+ d->typed_dump->emit_strings = OPTS_GET(opts, emit_strings, false);
ret = btf_dump_dump_type_data(d, NULL, t, id, data, 0, 0);
--
2.49.0.1204.g71687c7c1d-goog
Some C libraries may not define the ulong typedef that is commonly
available as a BSD/GNU extension. Add a fallback typedef to ensure ulong
is available across all selftest environments.
Signed-off-by: Aqib Faruqui <aqibaf(a)amazon.com>
---
tools/testing/selftests/kselftest.h | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/tools/testing/selftests/kselftest.h b/tools/testing/selftests/kselftest.h
index f362c6766..a1088a2af 100644
--- a/tools/testing/selftests/kselftest.h
+++ b/tools/testing/selftests/kselftest.h
@@ -58,6 +58,11 @@
#include <stdio.h>
#include <sys/utsname.h>
#include <sys/syscall.h>
+#include <sys/types.h>
+#endif
+
+#ifndef ulong
+typedef unsigned long ulong;
#endif
#ifndef ARRAY_SIZE
--
2.47.3
The original stdbuf use only checked if /usr/bin/stdbuf exists in the
host's system but failed to verify compatibility between stdbuf and the
target test binary.
The issue occurs when:
- Host system has glibc-based stdbuf from coreutils
- Selftest binaries are compiled with a non-glibc toolchain (cross
compilation)
The fix adds a runtime compatibility test against the target test binary
before enabling stdbuf, enabling cross-compiled selftests to run
successfully.
Signed-off-by: Aqib Faruqui <aqibaf(a)amazon.com>
---
tools/testing/selftests/kselftest/runner.sh | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/tools/testing/selftests/kselftest/runner.sh b/tools/testing/selftests/kselftest/runner.sh
index 2c3c58e65..8d4e33bd5 100644
--- a/tools/testing/selftests/kselftest/runner.sh
+++ b/tools/testing/selftests/kselftest/runner.sh
@@ -107,7 +107,7 @@ run_one()
echo "# Warning: file $TEST is missing!"
echo "not ok $test_num $TEST_HDR_MSG"
else
- if [ -x /usr/bin/stdbuf ]; then
+ if [ -x /usr/bin/stdbuf ] && [ -x "$TEST" ] && /usr/bin/stdbuf --output=L ldd "$TEST" >/dev/null 2>&1; then
stdbuf="/usr/bin/stdbuf --output=L "
fi
eval kselftest_cmd_args="\$${kselftest_cmd_args_ref:-}"
--
2.47.3
The rseq selftests rely on features provided by glibc that may not be
available in non-glibc C libraries:
1. The __GNU_PREREQ macro and glibc's thread pointer implementation are
not available in non-glibc libraries
2. The __NR_rseq syscall number may not be defined in non-glibc headers
Add a fallback thread pointer implementation for non-glibc systems using
the pre-existing inline assembly to access thread-local storage directly
via %fs/%gs registers. Also provide a fallback definition for __NR_rseq
when not already defined by the C library headers: 527 for alpha and 293
for other architectures.
Signed-off-by: Aqib Faruqui <aqibaf(a)amazon.com>
---
.../selftests/rseq/rseq-x86-thread-pointer.h | 14 ++++++++++++++
tools/testing/selftests/rseq/rseq.c | 8 ++++++++
2 files changed, 22 insertions(+)
diff --git a/tools/testing/selftests/rseq/rseq-x86-thread-pointer.h b/tools/testing/selftests/rseq/rseq-x86-thread-pointer.h
index d3133587d..a7c402926 100644
--- a/tools/testing/selftests/rseq/rseq-x86-thread-pointer.h
+++ b/tools/testing/selftests/rseq/rseq-x86-thread-pointer.h
@@ -14,6 +14,7 @@
extern "C" {
#endif
+#ifdef __GLIBC__
#if __GNUC_PREREQ (11, 1)
static inline void *rseq_thread_pointer(void)
{
@@ -32,6 +33,19 @@ static inline void *rseq_thread_pointer(void)
return __result;
}
#endif /* !GCC 11 */
+#else
+static inline void *rseq_thread_pointer(void)
+{
+ void *__result;
+
+# ifdef __x86_64__
+ __asm__ ("mov %%fs:0, %0" : "=r" (__result));
+# else
+ __asm__ ("mov %%gs:0, %0" : "=r" (__result));
+# endif
+ return __result;
+}
+#endif /* !__GLIBC__ */
#ifdef __cplusplus
}
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index 663a9cef1..1a6f73c98 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -36,6 +36,14 @@
#include "../kselftest.h"
#include "rseq.h"
+#ifndef __NR_rseq
+#ifdef __alpha__
+#define __NR_rseq 527
+#else
+#define __NR_rseq 293
+#endif
+#endif
+
/*
* Define weak versions to play nice with binaries that are statically linked
* against a libc that doesn't support registering its own rseq.
--
2.47.3
The backtrace() function is a GNU extension available in glibc but may
not be present in non-glibc libraries. KVM selftests use backtrace() for
error reporting and debugging.
Add conditional inclusion of execinfo.h only for glibc builds and
provide a weak stub implementation of backtrace() that returns 0 (stack
trace empty) for non-glibc systems.
Signed-off-by: Aqib Faruqui <aqibaf(a)amazon.com>
---
tools/testing/selftests/kvm/lib/assert.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/kvm/lib/assert.c b/tools/testing/selftests/kvm/lib/assert.c
index b49690658..c9778dc6c 100644
--- a/tools/testing/selftests/kvm/lib/assert.c
+++ b/tools/testing/selftests/kvm/lib/assert.c
@@ -6,11 +6,19 @@
*/
#include "test_util.h"
-#include <execinfo.h>
#include <sys/syscall.h>
+#ifdef __GLIBC__
+#include <execinfo.h> /* backtrace */
+#endif
+
#include "kselftest.h"
+int __attribute__((weak)) backtrace(void **buffer, int size)
+{
+ return 0;
+}
+
/* Dumps the current stack trace to stderr. */
static void __attribute__((noinline)) test_dump_stack(void);
static void test_dump_stack(void)
--
2.47.3
The kselftest harness uses pidfd_open() for test timeout handling but
may not have access to the syscall definitions in non-glibc
environments. Include pidfd.h to ensure the syscall numbers are
available.
Signed-off-by: Aqib Faruqui <aqibaf(a)amazon.com>
---
tools/testing/selftests/kselftest_harness.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/tools/testing/selftests/kselftest_harness.h b/tools/testing/selftests/kselftest_harness.h
index 2925e47db..1dd3e5a1b 100644
--- a/tools/testing/selftests/kselftest_harness.h
+++ b/tools/testing/selftests/kselftest_harness.h
@@ -69,6 +69,7 @@
#include <unistd.h>
#include "kselftest.h"
+#include "pidfd/pidfd.h"
#define TEST_TIMEOUT_DEFAULT 30
--
2.47.3