From: Guo Ren <guo...@linux.alibaba.com>
Add a static key controlling whether virt_spin_lock() should be
called or not. When running on bare metal set the new key to
false.
The VM guests should fall back to a Test-and-Set spinlock,
because fair locks have horrible lock 'holder' preemption issues.
The virt_spin_lock_key would shortcut for the queued_spin_lock_-
slowpath() function that allow virt_spin_lock to hijack it.
Signed-off-by: Guo Ren <guo...@linux.alibaba.com>
Signed-off-by: Guo Ren <guo...@kernel.org>
---
.../admin-guide/kernel-parameters.txt | 4 +++
arch/riscv/include/asm/spinlock.h | 22 ++++++++++++++++
arch/riscv/kernel/setup.c | 26 +++++++++++++++++++
3 files changed, 52 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 2ac9f1511774..b7794c96d91e 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3997,6 +3997,10 @@
no_uaccess_flush
[PPC] Don't flush the L1-D cache after accessing user
data.
+ no_virt_spin [RISC-V] Disable virt_spin_lock in VM guest to use
+ native_queued_spinlock when the nopvspin option is
enabled.
+ This would help vcpu=pcpu scenarios.
+
novmcoredd [KNL,KDUMP]
Disable device dump. Device dump allows drivers to
append dump data to vmcore so you can collect driver
diff --git a/arch/riscv/include/asm/spinlock.h
b/arch/riscv/include/asm/spinlock.h
index d07643c07aae..7bbcf3d9fff0 100644
--- a/arch/riscv/include/asm/spinlock.h
+++ b/arch/riscv/include/asm/spinlock.h
@@ -4,6 +4,28 @@
#define __ASM_RISCV_SPINLOCK_H
#ifdef CONFIG_QUEUED_SPINLOCKS
+/*
+ * The KVM guests fall back to a Test-and-Set spinlock, because fair locks
+ * have horrible lock 'holder' preemption issues. The virt_spin_lock_key
+ * would shortcut for the queued_spin_lock_slowpath() function that allow
+ * virt_spin_lock to hijack it.
+ */
+DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+#define virt_spin_lock virt_spin_lock
+static inline bool virt_spin_lock(struct qspinlock *lock)
+{
+ if (!static_branch_likely(&virt_spin_lock_key))
+ return false;
+
+ do {
+ while (atomic_read(&lock->val) != 0)
+ cpu_relax();
+ } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0);
+
+ return true;
+}
+
#define _Q_PENDING_LOOPS (1 << 9)
#endif
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index d9072a59831c..0bafb9fd6ea3 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -27,6 +27,7 @@
#include <asm/cacheflush.h>
#include <asm/cpufeature.h>
#include <asm/cpu_ops.h>
+#include <asm/cpufeature.h>
#include <asm/early_ioremap.h>
#include <asm/pgtable.h>
#include <asm/setup.h>
@@ -266,6 +267,27 @@ early_param("qspinlock", queued_spinlock_setup);
DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key);
EXPORT_SYMBOL(combo_qspinlock_key);
+#ifdef CONFIG_QUEUED_SPINLOCKS
+static bool no_virt_spin __ro_after_init;
+static int __init no_virt_spin_setup(char *p)
+{
+ no_virt_spin = true;
+
+ return 0;
+}
+early_param("no_virt_spin", no_virt_spin_setup);
+
+DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+static void __init virt_spin_lock_init(void)
+{
+ if (no_virt_spin)
+ static_branch_disable(&virt_spin_lock_key);
+ else
+ pr_info("Enable virt_spin_lock\n");
+}
+#endif
+
static void __init riscv_spinlock_init(void)
{
if (!enable_qspinlock) {
@@ -274,6 +296,10 @@ static void __init riscv_spinlock_init(void)
} else {
pr_info("Queued spinlock: enabled\n");
}
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+ virt_spin_lock_init();
+#endif
}
#endif
--
2.40.1
