[RFC PATCH for 5.8 3/4] rseq: Introduce RSEQ_FLAG_RELIABLE_CPU_ID
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: 2020-07-06 20:49:49
Also in:
lkml
Subsystem:
restartable sequences support, the rest · Maintainers:
Mathieu Desnoyers, Peter Zijlstra, "Paul E. McKenney", Boqun Feng, Linus Torvalds
commit 93b585c08d16 ("Fix: sched: unreliable rseq cpu_id for new tasks")
addresses an issue with cpu_id field of newly created processes. Expose
a flag which can be used by user-space to query whether the kernel
implements this fix.
Considering that this issue can cause corruption of user-space per-cpu
data updated with rseq, it is recommended that user-space detects
availability of this fix by using the RSEQ_FLAG_RELIABLE_CPU_ID flag
either combined with registration or on its own before using rseq.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Thomas Gleixner <redacted>
Cc: Florian Weimer <redacted>
Cc: "Paul E. McKenney" <redacted>
Cc: Boqun Feng <redacted>
Cc: "H . Peter Anvin" <hpa@zytor.com>
Cc: Paul Turner <redacted>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Neel Natu <redacted>
Cc: linux-api@vger.kernel.org
---
include/uapi/linux/rseq.h | 5 +++++
kernel/rseq.c | 4 ++++
2 files changed, 9 insertions(+)
diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h
index 3b5fba25461a..a548b77c9520 100644
--- a/include/uapi/linux/rseq.h
+++ b/include/uapi/linux/rseq.h@@ -21,13 +21,18 @@ enum rseq_cpu_id_state { /* * RSEQ_FLAG_UNREGISTER: Unregister rseq ABI for caller thread. * RSEQ_FLAG_REGISTER: Register rseq ABI for caller thread. + * RSEQ_FLAG_RELIABLE_CPU_ID: rseq provides a reliable cpu_id field. * * Flag value 0 has the same behavior as RSEQ_FLAG_REGISTER, but cannot be * combined with other flags. This behavior is kept for backward compatibility. + * + * The flag RSEQ_FLAG_REGISTER can be combined with the RSEQ_FLAG_RELIABLE_CPU_ID + * flag. */ enum rseq_flags { RSEQ_FLAG_UNREGISTER = (1 << 0), RSEQ_FLAG_REGISTER = (1 << 1), + RSEQ_FLAG_RELIABLE_CPU_ID = (1 << 2), }; enum rseq_cs_flags_bit {
diff --git a/kernel/rseq.c b/kernel/rseq.c
index 47ce221cd6f9..32cc2e0d961f 100644
--- a/kernel/rseq.c
+++ b/kernel/rseq.c@@ -333,6 +333,8 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, current->rseq_sig = 0; break; case RSEQ_FLAG_REGISTER: + fallthrough; + case RSEQ_FLAG_REGISTER | RSEQ_FLAG_RELIABLE_CPU_ID: if (current->rseq) { /* * If rseq is already registered, check whether
@@ -365,6 +367,8 @@ SYSCALL_DEFINE4(rseq, struct rseq __user *, rseq, u32, rseq_len, */ rseq_set_notify_resume(current); break; + case RSEQ_FLAG_RELIABLE_CPU_ID: + break; default: return -EINVAL; }
--
2.17.1