Commit-ID: 0fb9a1abc8c97f858997e962694eb36b4517144e
Gitweb: https://git.kernel.org/tip/0fb9a1abc8c97f858997e962694eb36b4517144e
Author: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
AuthorDate: Mon, 9 Jul 2018 15:51:52 -0400
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Tue, 10 Jul 2018 22:18:52 +0200
rseq: uapi: Update uapi comments
Update rseq uapi header comments to reflect that user-space need to do
thread-local loads/stores from/to the struct rseq fields.
As a consequence of this added requirement, the kernel does not need
to perform loads/stores with single-copy atomicity.
Update the comment associated to the "flags" fields to describe
more accurately that it's only useful to facilitate single-stepping
through rseq critical sections with debuggers.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-api@xxxxxxxxxxxxxxx
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: "Paul E . McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
Cc: Dave Watson <davejwatson@xxxxxx>
Cc: Paul Turner <pjt@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: Andi Kleen <andi@xxxxxxxxxxxxxx>
Cc: Chris Lameter <cl@xxxxxxxxx>
Cc: Ben Maurer <bmaurer@xxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Link: https://lkml.kernel.org/r/20180709195155.7654-4-mathieu.desnoyers@xxxxxxxxxxxx
---
include/uapi/linux/rseq.h | 69 ++++++++++++++++++++++++-----------------------
kernel/rseq.c | 2 +-
2 files changed, 37 insertions(+), 34 deletions(-)
diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index 519ad6e176d1..bf4188c13bec 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h
@@ -67,28 +67,30 @@ struct rseq_cs {
struct rseq {
/*
* Restartable sequences cpu_id_start field. Updated by the
- * kernel, and read by user-space with single-copy atomicity
- * semantics. 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.
+ * 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,
- * and read by user-space with single-copy atomicity semantics.
- * 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.
+ * 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;
/*
@@ -105,27 +107,28 @@ struct rseq {
* 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 with single-copy atomicity semantics.
- * Set by user-space with single-copy atomicity semantics. Aligned
- * on 64-bit.
+ * 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.
*/
LINUX_FIELD_u32_u64(rseq_cs);
/*
- * - RSEQ_DISABLE flag:
+ * 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.
*
- * Fallback fast-track flag for single-stepping.
- * Set by user-space if lack of progress is detected.
- * Cleared by user-space after rseq finish.
- * Read by the kernel.
* - RSEQ_CS_FLAG_NO_RESTART_ON_PREEMPT
- * Inhibit instruction sequence block restart and event
- * counter increment on preemption for this thread.
+ * Inhibit instruction sequence block restart on preemption
+ * for this thread.
* - RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL
- * Inhibit instruction sequence block restart and event
- * counter increment on signal delivery for this thread.
+ * Inhibit instruction sequence block restart on signal
+ * delivery for this thread.
* - RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE
- * Inhibit instruction sequence block restart and event
- * counter increment on migration for this thread.
+ * Inhibit instruction sequence block restart on migration for
+ * this thread.
*/
__u32 flags;
} __attribute__((aligned(4 * sizeof(__u64))));
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 2c8463acb50d..2a7748675be7 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c
@@ -201,7 +201,7 @@ static int clear_rseq_cs(struct task_struct *t)
* of code outside of the rseq assembly block. This performs
* a lazy clear of the rseq_cs field.
*
- * Set rseq_cs to NULL with single-copy atomicity.
+ * Set rseq_cs to NULL.
*/
return put_user(0UL, &t->rseq->rseq_cs);
}
--
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