We ripped out PV and virtualization related bits from rqspinlock in an
earlier commit, however, a fair lock performs poorly within a virtual
machine when the lock holder is preempted. As such, retain the
virt_spin_lock fallback to test and set lock, but with timeout and
deadlock detection.
We don't integrate support for CONFIG_PARAVIRT_SPINLOCKS yet, as that
requires more involved algorithmic changes and introduces more
complexity. It can be done when the need arises in the future.
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
---
arch/x86/include/asm/rqspinlock.h | 20 ++++++++++++++++
include/asm-generic/rqspinlock.h | 7 ++++++
kernel/locking/rqspinlock.c | 38 +++++++++++++++++++++++++++++++
3 files changed, 65 insertions(+)
create mode 100644 arch/x86/include/asm/rqspinlock.h
diff --git a/arch/x86/include/asm/rqspinlock.h b/arch/x86/include/asm/rqspinlock.h
new file mode 100644
index 000000000000..ecfb7dfe6370
--- /dev/null
+++ b/arch/x86/include/asm/rqspinlock.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_RQSPINLOCK_H
+#define _ASM_X86_RQSPINLOCK_H
+
+#include <asm/paravirt.h>
+
+#ifdef CONFIG_PARAVIRT
+DECLARE_STATIC_KEY_FALSE(virt_spin_lock_key);
+
+#define resilient_virt_spin_lock_enabled resilient_virt_spin_lock_enabled
+static __always_inline bool resilient_virt_spin_lock_enabled(void)
+{
+ return static_branch_likely(&virt_spin_lock_key);
+}
+
+#endif /* CONFIG_PARAVIRT */
+
+#include <asm-generic/rqspinlock.h>
+
+#endif /* _ASM_X86_RQSPINLOCK_H */
diff --git a/include/asm-generic/rqspinlock.h b/include/asm-generic/rqspinlock.h
index c7e33ccc57a6..dc436ab01471 100644
--- a/include/asm-generic/rqspinlock.h
+++ b/include/asm-generic/rqspinlock.h
@@ -17,6 +17,13 @@ struct qspinlock;
extern int resilient_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val, u64 timeout);
+#ifndef resilient_virt_spin_lock_enabled
+static __always_inline bool resilient_virt_spin_lock_enabled(void)
+{
+ return false;
+}
+#endif
+
/*
* Default timeout for waiting loops is 0.5 seconds
*/
diff --git a/kernel/locking/rqspinlock.c b/kernel/locking/rqspinlock.c
index b7c86127d288..e397f91ebcf6 100644
--- a/kernel/locking/rqspinlock.c
+++ b/kernel/locking/rqspinlock.c
@@ -247,6 +247,41 @@ static noinline int check_timeout(struct qspinlock *lock, u32 mask,
*/
#define RES_RESET_TIMEOUT(ts) ({ (ts).timeout_end = 0; })
+#ifdef CONFIG_PARAVIRT
+
+static inline int resilient_virt_spin_lock(struct qspinlock *lock, struct rqspinlock_timeout *ts)
+{
+ int val, ret = 0;
+
+ RES_RESET_TIMEOUT(*ts);
+ grab_held_lock_entry(lock);
+retry:
+ val = atomic_read(&lock->val);
+
+ if (val || !atomic_try_cmpxchg(&lock->val, &val, _Q_LOCKED_VAL)) {
+ if (RES_CHECK_TIMEOUT(*ts, ret, ~0u)) {
+ lockevent_inc(rqspinlock_lock_timeout);
+ goto timeout;
+ }
+ cpu_relax();
+ goto retry;
+ }
+
+ return 0;
+timeout:
+ release_held_lock_entry();
+ return ret;
+}
+
+#else
+
+static __always_inline int resilient_virt_spin_lock(struct qspinlock *lock, struct rqspinlock_timeout *ts)
+{
+ return 0;
+}
+
+#endif /* CONFIG_PARAVIRT */
+
/*
* Per-CPU queue node structures; we can never have more than 4 nested
* contexts: task, softirq, hardirq, nmi.
@@ -287,6 +322,9 @@ int __lockfunc resilient_queued_spin_lock_slowpath(struct qspinlock *lock, u32 v
RES_INIT_TIMEOUT(ts, timeout);
+ if (resilient_virt_spin_lock_enabled())
+ return resilient_virt_spin_lock(lock, &ts);
+
/*
* Wait for in-progress pending->locked hand-overs with a bounded
* number of spins so that we guarantee forward progress.
--
2.43.5
