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Message-Id: <20220124171253.22072-2-mathieu.desnoyers@efficios.com>
Date: Mon, 24 Jan 2022 12:12:39 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org,
Peter Zijlstra <peterz@...radead.org>,
"Paul E . McKenney" <paulmck@...nel.org>,
Boqun Feng <boqun.feng@...il.com>,
"H . Peter Anvin" <hpa@...or.com>, Paul Turner <pjt@...gle.com>,
linux-api@...r.kernel.org, Shuah Khan <shuah@...nel.org>,
linux-kselftest@...r.kernel.org,
Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Subject: [RFC PATCH 01/15] selftests/rseq: introduce own copy of rseq uapi header
The Linux kernel rseq uapi header has a broken layout for the
rseq_cs.ptr field on 32-bit little endian architectures. The entire
rseq_cs.ptr field is planned for removal, leaving only the 64-bit
rseq_cs.ptr64 field available.
Both glibc and librseq use their own copy of the Linux kernel uapi
header, where they introduce proper union fields to access to the 32-bit
low order bits of the rseq_cs pointer on 32-bit architectures.
Introduce a copy of the Linux kernel uapi headers in the Linux kernel
selftests.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
---
tools/testing/selftests/rseq/rseq-abi.h | 151 ++++++++++++++++++++++++
tools/testing/selftests/rseq/rseq.c | 14 +--
tools/testing/selftests/rseq/rseq.h | 10 +-
3 files changed, 161 insertions(+), 14 deletions(-)
create mode 100644 tools/testing/selftests/rseq/rseq-abi.h
diff --git a/tools/testing/selftests/rseq/rseq-abi.h b/tools/testing/selftests/rseq/rseq-abi.h
new file mode 100644
index 000000000000..a8c44d9af71f
--- /dev/null
+++ b/tools/testing/selftests/rseq/rseq-abi.h
@@ -0,0 +1,151 @@
+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+#ifndef _RSEQ_ABI_H
+#define _RSEQ_ABI_H
+
+/*
+ * rseq-abi.h
+ *
+ * Restartable sequences system call API
+ *
+ * Copyright (c) 2015-2022 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
+ */
+
+#include <linux/types.h>
+#include <asm/byteorder.h>
+
+enum rseq_abi_cpu_id_state {
+ RSEQ_ABI_CPU_ID_UNINITIALIZED = -1,
+ RSEQ_ABI_CPU_ID_REGISTRATION_FAILED = -2,
+};
+
+enum rseq_abi_flags {
+ RSEQ_ABI_FLAG_UNREGISTER = (1 << 0),
+};
+
+enum rseq_abi_cs_flags_bit {
+ RSEQ_ABI_CS_FLAG_NO_RESTART_ON_PREEMPT_BIT = 0,
+ RSEQ_ABI_CS_FLAG_NO_RESTART_ON_SIGNAL_BIT = 1,
+ RSEQ_ABI_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT = 2,
+};
+
+enum rseq_abi_cs_flags {
+ RSEQ_ABI_CS_FLAG_NO_RESTART_ON_PREEMPT =
+ (1U << RSEQ_ABI_CS_FLAG_NO_RESTART_ON_PREEMPT_BIT),
+ RSEQ_ABI_CS_FLAG_NO_RESTART_ON_SIGNAL =
+ (1U << RSEQ_ABI_CS_FLAG_NO_RESTART_ON_SIGNAL_BIT),
+ RSEQ_ABI_CS_FLAG_NO_RESTART_ON_MIGRATE =
+ (1U << RSEQ_ABI_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT),
+};
+
+/*
+ * struct rseq_abi_cs is aligned on 4 * 8 bytes to ensure it is always
+ * contained within a single cache-line. It is usually declared as
+ * link-time constant data.
+ */
+struct rseq_abi_cs {
+ /* Version of this structure. */
+ __u32 version;
+ /* enum rseq_abi_cs_flags */
+ __u32 flags;
+ __u64 start_ip;
+ /* Offset from start_ip. */
+ __u64 post_commit_offset;
+ __u64 abort_ip;
+} __attribute__((aligned(4 * sizeof(__u64))));
+
+/*
+ * struct rseq_abi is aligned on 4 * 8 bytes to ensure it is always
+ * contained within a single cache-line.
+ *
+ * A single struct rseq_abi per thread is allowed.
+ */
+struct rseq_abi {
+ /*
+ * Restartable sequences cpu_id_start field. Updated by the
+ * kernel. Read by user-space with single-copy atomicity
+ * semantics. This field should only be read by the thread which
+ * registered this data structure. Aligned on 32-bit. Always
+ * contains a value in the range of possible CPUs, although the
+ * value may not be the actual current CPU (e.g. if rseq is not
+ * initialized). This CPU number value should always be compared
+ * against the value of the cpu_id field before performing a rseq
+ * commit or returning a value read from a data structure indexed
+ * using the cpu_id_start value.
+ */
+ __u32 cpu_id_start;
+ /*
+ * Restartable sequences cpu_id field. Updated by the kernel.
+ * Read by user-space with single-copy atomicity semantics. This
+ * field should only be read by the thread which registered this
+ * data structure. Aligned on 32-bit. Values
+ * RSEQ_CPU_ID_UNINITIALIZED and RSEQ_CPU_ID_REGISTRATION_FAILED
+ * have a special semantic: the former means "rseq uninitialized",
+ * and latter means "rseq initialization failed". This value is
+ * meant to be read within rseq critical sections and compared
+ * with the cpu_id_start value previously read, before performing
+ * the commit instruction, or read and compared with the
+ * cpu_id_start value before returning a value loaded from a data
+ * structure indexed using the cpu_id_start value.
+ */
+ __u32 cpu_id;
+ /*
+ * Restartable sequences rseq_cs field.
+ *
+ * Contains NULL when no critical section is active for the current
+ * thread, or holds a pointer to the currently active struct rseq_cs.
+ *
+ * Updated by user-space, which sets the address of the currently
+ * active rseq_cs at the beginning of assembly instruction sequence
+ * block, and set to NULL by the kernel when it restarts an assembly
+ * instruction sequence block, as well as when the kernel detects that
+ * it is preempting or delivering a signal outside of the range
+ * targeted by the rseq_cs. Also needs to be set to NULL by user-space
+ * before reclaiming memory that contains the targeted struct rseq_cs.
+ *
+ * Read and set by the kernel. Set by user-space with single-copy
+ * atomicity semantics. This field should only be updated by the
+ * thread which registered this data structure. Aligned on 64-bit.
+ */
+ union {
+ __u64 ptr64;
+
+ /*
+ * The "arch" field provides architecture accessor for
+ * the ptr field based on architecture pointer size and
+ * endianness.
+ */
+ struct {
+#ifdef __LP64__
+ __u64 ptr;
+#elif defined(__BYTE_ORDER) ? (__BYTE_ORDER == __BIG_ENDIAN) : defined(__BIG_ENDIAN)
+ __u32 padding; /* Initialized to zero. */
+ __u32 ptr;
+#else
+ __u32 ptr;
+ __u32 padding; /* Initialized to zero. */
+#endif
+ } arch;
+ } rseq_cs;
+
+ /*
+ * Restartable sequences flags field.
+ *
+ * This field should only be updated by the thread which
+ * registered this data structure. Read by the kernel.
+ * Mainly used for single-stepping through rseq critical sections
+ * with debuggers.
+ *
+ * - RSEQ_ABI_CS_FLAG_NO_RESTART_ON_PREEMPT
+ * Inhibit instruction sequence block restart on preemption
+ * for this thread.
+ * - RSEQ_ABI_CS_FLAG_NO_RESTART_ON_SIGNAL
+ * Inhibit instruction sequence block restart on signal
+ * delivery for this thread.
+ * - RSEQ_ABI_CS_FLAG_NO_RESTART_ON_MIGRATE
+ * Inhibit instruction sequence block restart on migration for
+ * this thread.
+ */
+ __u32 flags;
+} __attribute__((aligned(4 * sizeof(__u64))));
+
+#endif /* _RSEQ_ABI_H */
diff --git a/tools/testing/selftests/rseq/rseq.c b/tools/testing/selftests/rseq/rseq.c
index fb440dfca158..bfe1b2692ffc 100644
--- a/tools/testing/selftests/rseq/rseq.c
+++ b/tools/testing/selftests/rseq/rseq.c
@@ -30,8 +30,8 @@
#include "../kselftest.h"
#include "rseq.h"
-__thread volatile struct rseq __rseq_abi = {
- .cpu_id = RSEQ_CPU_ID_UNINITIALIZED,
+__thread volatile struct rseq_abi __rseq_abi = {
+ .cpu_id = RSEQ_ABI_CPU_ID_UNINITIALIZED,
};
/*
@@ -66,7 +66,7 @@ static void signal_restore(sigset_t oldset)
abort();
}
-static int sys_rseq(volatile struct rseq *rseq_abi, uint32_t rseq_len,
+static int sys_rseq(volatile struct rseq_abi *rseq_abi, uint32_t rseq_len,
int flags, uint32_t sig)
{
return syscall(__NR_rseq, rseq_abi, rseq_len, flags, sig);
@@ -86,13 +86,13 @@ int rseq_register_current_thread(void)
}
if (__rseq_refcount++)
goto end;
- rc = sys_rseq(&__rseq_abi, sizeof(struct rseq), 0, RSEQ_SIG);
+ rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi), 0, RSEQ_SIG);
if (!rc) {
assert(rseq_current_cpu_raw() >= 0);
goto end;
}
if (errno != EBUSY)
- __rseq_abi.cpu_id = RSEQ_CPU_ID_REGISTRATION_FAILED;
+ __rseq_abi.cpu_id = RSEQ_ABI_CPU_ID_REGISTRATION_FAILED;
ret = -1;
__rseq_refcount--;
end:
@@ -114,8 +114,8 @@ int rseq_unregister_current_thread(void)
}
if (--__rseq_refcount)
goto end;
- rc = sys_rseq(&__rseq_abi, sizeof(struct rseq),
- RSEQ_FLAG_UNREGISTER, RSEQ_SIG);
+ rc = sys_rseq(&__rseq_abi, sizeof(struct rseq_abi),
+ RSEQ_ABI_FLAG_UNREGISTER, RSEQ_SIG);
if (!rc)
goto end;
__rseq_refcount = 1;
diff --git a/tools/testing/selftests/rseq/rseq.h b/tools/testing/selftests/rseq/rseq.h
index 3f63eb362b92..cb6bbc53b586 100644
--- a/tools/testing/selftests/rseq/rseq.h
+++ b/tools/testing/selftests/rseq/rseq.h
@@ -16,7 +16,7 @@
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
-#include <linux/rseq.h>
+#include "rseq-abi.h"
/*
* Empty code injection macros, override when testing.
@@ -43,7 +43,7 @@
#define RSEQ_INJECT_FAILED
#endif
-extern __thread volatile struct rseq __rseq_abi;
+extern __thread volatile struct rseq_abi __rseq_abi;
extern int __rseq_handled;
#define rseq_likely(x) __builtin_expect(!!(x), 1)
@@ -139,11 +139,7 @@ static inline uint32_t rseq_current_cpu(void)
static inline void rseq_clear_rseq_cs(void)
{
-#ifdef __LP64__
- __rseq_abi.rseq_cs.ptr = 0;
-#else
- __rseq_abi.rseq_cs.ptr.ptr32 = 0;
-#endif
+ __rseq_abi.rseq_cs.arch.ptr = 0;
}
/*
--
2.17.1
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