From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
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 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.
Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
.../admin-guide/kernel-parameters.txt | 4 +++
arch/riscv/include/asm/sbi.h | 8 +++++
arch/riscv/include/asm/spinlock.h | 22 ++++++++++++++
arch/riscv/kernel/sbi.c | 2 +-
arch/riscv/kernel/setup.c | 30 ++++++++++++++++++-
5 files changed, 64 insertions(+), 2 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 61cacb8dfd0e..f75bedc50e00 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3927,6 +3927,10 @@
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 KVM 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/sbi.h b/arch/riscv/include/asm/sbi.h
index 501e06e52078..e0233b3d7a5f 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -50,6 +50,13 @@ enum sbi_ext_base_fid {
SBI_EXT_BASE_GET_MIMPID,
};
+enum sbi_ext_base_impl_id {
+ SBI_EXT_BASE_IMPL_ID_BBL = 0,
+ SBI_EXT_BASE_IMPL_ID_OPENSBI,
+ SBI_EXT_BASE_IMPL_ID_XVISOR,
+ SBI_EXT_BASE_IMPL_ID_KVM,
+};
+
enum sbi_ext_time_fid {
SBI_EXT_TIME_SET_TIMER = 0,
};
@@ -269,6 +276,7 @@ int sbi_console_getchar(void);
long sbi_get_mvendorid(void);
long sbi_get_marchid(void);
long sbi_get_mimpid(void);
+long sbi_get_firmware_id(void);
void sbi_set_timer(uint64_t stime_value);
void sbi_shutdown(void);
void sbi_send_ipi(unsigned int cpu);
diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
index 8ea0fee80652..6b38d6616f14 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/sbi.c b/arch/riscv/kernel/sbi.c
index 88eea3a99ee0..cdd45edc8db4 100644
--- a/arch/riscv/kernel/sbi.c
+++ b/arch/riscv/kernel/sbi.c
@@ -555,7 +555,7 @@ static inline long sbi_get_spec_version(void)
return __sbi_base_ecall(SBI_EXT_BASE_GET_SPEC_VERSION);
}
-static inline long sbi_get_firmware_id(void)
+long sbi_get_firmware_id(void)
{
return __sbi_base_ecall(SBI_EXT_BASE_GET_IMP_ID);
}
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 0f084f037651..c57d15b05160 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -26,6 +26,7 @@
#include <asm/alternative.h>
#include <asm/cacheflush.h>
#include <asm/cpu_ops.h>
+#include <asm/cpufeature.h>
#include <asm/early_ioremap.h>
#include <asm/pgtable.h>
#include <asm/setup.h>
@@ -283,16 +284,43 @@ DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key);
EXPORT_SYMBOL(combo_qspinlock_key);
#endif
+#ifdef CONFIG_QUEUED_SPINLOCKS
+static bool no_virt_spin_key = false;
+DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+static int __init no_virt_spin_setup(char *p)
+{
+ no_virt_spin_key = true;
+
+ return 0;
+}
+early_param("no_virt_spin", no_virt_spin_setup);
+
+static void __init virt_spin_lock_init(void)
+{
+ if (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM ||
+ no_virt_spin_key)
+ static_branch_disable(&virt_spin_lock_key);
+ else
+ pr_info("Enable virt_spin_lock\n");
+}
+#endif
+
static void __init riscv_spinlock_init(void)
{
#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
- if (!enable_qspinlock_key) {
+ if (!enable_qspinlock_key &&
+ (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)) {
static_branch_disable(&combo_qspinlock_key);
pr_info("Ticket spinlock: enabled\n");
} else {
pr_info("Queued spinlock: enabled\n");
}
#endif
+
+#ifdef CONFIG_QUEUED_SPINLOCKS
+ virt_spin_lock_init();
+#endif
}
extern void __init init_rt_signal_env(void);
--
2.36.1
