[PATCH 2/2] LoongArch: KVM: Add paravirt qspinlock in guest side

Bibo Mao
2024-07-23T07:38:30Z

Option PARAVIRT_SPINLOCKS is added on LoongArch system, and
pv_lock_ops template is added here. If option PARAVIRT_SPINLOCKS
is enabled, the native ops works on host machine.

Two functions kvm_wait() and kvm_kick_cpu() are added specicial for
VM, if VM detects hypervisor supports pv spinlock. With kvm_wait()
vCPU thread will exit to hypervisor and give up scheduleing on pCPU,
and with function kvm_kick_cpu() one hypercall function is used
to notify hypervisor to wakeup previously waited vCPU.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
---
arch/loongarch/Kconfig | 14 +++
arch/loongarch/include/asm/Kbuild | 1 -
arch/loongarch/include/asm/paravirt.h | 47 ++++++++++
arch/loongarch/include/asm/qspinlock.h | 39 ++++++++
.../include/asm/qspinlock_paravirt.h | 6 ++
arch/loongarch/kernel/paravirt.c | 88 +++++++++++++++++++
arch/loongarch/kernel/smp.c | 4 +-
7 files changed, 197 insertions(+), 2 deletions(-)
create mode 100644 arch/loongarch/include/asm/qspinlock.h
create mode 100644 arch/loongarch/include/asm/qspinlock_paravirt.h

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index b81d0eba5c7e..7ad63db2fafd 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -660,6 +660,20 @@ config PARAVIRT_TIME_ACCOUNTING

If in doubt, say N here.

+config PARAVIRT_SPINLOCKS
+ bool "Paravirtual queued spinlocks"
+ select PARAVIRT
+ depends on SMP
+ help
+ Paravirtualized spinlocks allow a pvops backend to replace the
+ spinlock implementation with something virtualization-friendly
+ (for example, block the virtual CPU rather than spinning).
+
+ It has a minimal impact on native kernels and gives a nice performance
+ benefit on paravirtualized kernels.
+
+ If you are unsure how to answer this question, answer Y.
+
endmenu

config ARCH_SELECT_MEMORY_MODEL
diff --git a/arch/loongarch/include/asm/Kbuild b/arch/loongarch/include/asm/Kbuild
index 2bb3676429c0..4635b755b2b4 100644
--- a/arch/loongarch/include/asm/Kbuild
+++ b/arch/loongarch/include/asm/Kbuild
@@ -6,7 +6,6 @@ generic-y += mcs_spinlock.h
generic-y += parport.h
generic-y += early_ioremap.h
generic-y += qrwlock.h
-generic-y += qspinlock.h
generic-y += user.h
generic-y += ioctl.h
generic-y += statfs.h
diff --git a/arch/loongarch/include/asm/paravirt.h b/arch/loongarch/include/asm/paravirt.h
index dddec49671ae..2617d635171b 100644
--- a/arch/loongarch/include/asm/paravirt.h
+++ b/arch/loongarch/include/asm/paravirt.h
@@ -20,6 +20,47 @@ static inline u64 paravirt_steal_clock(int cpu)
int __init pv_ipi_init(void);
int __init pv_time_init(void);

+#if defined(CONFIG_PARAVIRT_SPINLOCKS)
+struct qspinlock;
+struct pv_lock_ops {
+ void (*queued_spin_lock_slowpath)(struct qspinlock *lock, u32 val);
+ void (*queued_spin_unlock)(struct qspinlock *lock);
+ void (*wait)(u8 *ptr, u8 val);
+ void (*kick)(int cpu);
+ bool (*vcpu_is_preempted)(int cpu);
+};
+
+extern struct pv_lock_ops pv_lock_ops;
+
+void __init kvm_spinlock_init(void);
+bool pv_is_native_spin_unlock(void);
+
+static __always_inline void pv_queued_spin_lock_slowpath(struct qspinlock *lock,
+ u32 val)
+{
+ pv_lock_ops.queued_spin_lock_slowpath(lock, val);
+}
+
+static __always_inline void pv_queued_spin_unlock(struct qspinlock *lock)
+{
+ pv_lock_ops.queued_spin_unlock(lock);
+}
+
+static __always_inline void pv_wait(u8 *ptr, u8 val)
+{
+ pv_lock_ops.wait(ptr, val);
+}
+
+static __always_inline void pv_kick(int cpu)
+{
+ pv_lock_ops.kick(cpu);
+}
+
+static __always_inline bool pv_vcpu_is_preempted(long cpu)
+{
+ return pv_lock_ops.vcpu_is_preempted(cpu);
+}
+#endif /* PARAVIRT_SPINLOCKS */
#else

static inline int pv_ipi_init(void)
@@ -32,4 +73,10 @@ static inline int pv_time_init(void)
return 0;
}
#endif // CONFIG_PARAVIRT
+
+#ifndef CONFIG_PARAVIRT_SPINLOCKS
+static inline void kvm_spinlock_init(void)
+{
+}
+#endif
#endif
diff --git a/arch/loongarch/include/asm/qspinlock.h b/arch/loongarch/include/asm/qspinlock.h
new file mode 100644
index 000000000000..8e1b14c9e906
--- /dev/null
+++ b/arch/loongarch/include/asm/qspinlock.h
@@ -0,0 +1,39 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_LOONGARCH_QSPINLOCK_H
+#define _ASM_LOONGARCH_QSPINLOCK_H
+
+#include <asm/paravirt.h>
+
+#define _Q_PENDING_LOOPS (1 << 9)
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+/* How long a lock should spin before we consider blocking */
+#define SPIN_THRESHOLD (1 << 15)
+
+extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __pv_init_lock_hash(void);
+extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
+extern void __pv_queued_spin_unlock(struct qspinlock *lock);
+extern bool nopvspin;
+
+static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
+{
+ pv_queued_spin_lock_slowpath(lock, val);
+}
+
+#define queued_spin_unlock queued_spin_unlock
+static inline void queued_spin_unlock(struct qspinlock *lock)
+{
+ pv_queued_spin_unlock(lock);
+}
+
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(long cpu)
+{
+ return pv_vcpu_is_preempted(cpu);
+}
+#endif
+
+#include <asm-generic/qspinlock.h>
+
+#endif // _ASM_LOONGARCH_QSPINLOCK_H
diff --git a/arch/loongarch/include/asm/qspinlock_paravirt.h b/arch/loongarch/include/asm/qspinlock_paravirt.h
new file mode 100644
index 000000000000..d6d7f487daea
--- /dev/null
+++ b/arch/loongarch/include/asm/qspinlock_paravirt.h
@@ -0,0 +1,6 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_QSPINLOCK_PARAVIRT_H
+#define __ASM_QSPINLOCK_PARAVIRT_H
+
+void __lockfunc __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked);
+#endif
diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
index aee44610007d..758039eabdde 100644
--- a/arch/loongarch/kernel/paravirt.c
+++ b/arch/loongarch/kernel/paravirt.c
@@ -298,3 +298,91 @@ int __init pv_time_init(void)

return 0;
}
+
+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+static bool native_vcpu_is_preempted(int cpu)
+{
+ return false;
+}
+
+/**
+ * queued_spin_unlock - release a queued spinlock
+ * @lock : Pointer to queued spinlock structure
+ */
+static void native_queued_spin_unlock(struct qspinlock *lock)
+{
+ /*
+ * unlock() needs release semantics:
+ */
+ smp_store_release(&lock->locked, 0);
+}
+
+static void paravirt_nop_kick(int cpu)
+{
+}
+
+static void paravirt_nop_wait(u8 *ptr, u8 val)
+{
+}
+
+static void kvm_wait(u8 *ptr, u8 val)
+{
+ if (READ_ONCE(*ptr) != val)
+ return;
+
+ __asm__ __volatile__("idle 0\n\t" : : : "memory");
+}
+
+/* Kick a cpu. Used to wake up a halted vcpu */
+static void kvm_kick_cpu(int cpu)
+{
+ kvm_hypercall1(KVM_HCALL_FUNC_KICK, cpu_logical_map(cpu));
+}
+
+bool pv_is_native_spin_unlock(void)
+{
+ return pv_lock_ops.queued_spin_unlock == native_queued_spin_unlock;
+}
+
+/*
+ * Setup pv_lock_ops for guest kernel.
+ */
+void __init kvm_spinlock_init(void)
+{
+ int feature;
+
+ /*
+ * pv_hash()/pv_unhas() need it whatever pv spinlock is
+ * enabled or not
+ */
+ __pv_init_lock_hash();
+
+ if (!kvm_para_available())
+ return;
+
+ /* Don't use the pvqspinlock code if there is only 1 vCPU. */
+ if (num_possible_cpus() == 1)
+ return;
+
+ feature = kvm_arch_para_features();
+ if (!(feature & KVM_FEATURE_PARAVIRT_SPINLOCK))
+ return;
+
+ if (nopvspin)
+ return;
+
+ pr_info("Using paravirt qspinlock\n");
+ pv_lock_ops.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
+ pv_lock_ops.queued_spin_unlock = __pv_queued_spin_unlock;
+ pv_lock_ops.wait = kvm_wait;
+ pv_lock_ops.kick = kvm_kick_cpu;
+}
+
+struct pv_lock_ops pv_lock_ops = {
+ .queued_spin_lock_slowpath = native_queued_spin_lock_slowpath,
+ .queued_spin_unlock = native_queued_spin_unlock,
+ .wait = paravirt_nop_wait,
+ .kick = paravirt_nop_kick,
+ .vcpu_is_preempted = native_vcpu_is_preempted,
+};
+#endif /* CONFIG_PARAVIRT_SPINLOCKS */
diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c
index 1436d2465939..6bc0b182a2ce 100644
--- a/arch/loongarch/kernel/smp.c
+++ b/arch/loongarch/kernel/smp.c
@@ -463,7 +463,7 @@ core_initcall(ipi_pm_init);
#endif

/* Preload SMP state for boot cpu */
-void smp_prepare_boot_cpu(void)
+void __init smp_prepare_boot_cpu(void)
{
unsigned int cpu, node, rr_node;

@@ -496,6 +496,8 @@ void smp_prepare_boot_cpu(void)
rr_node = next_node_in(rr_node, node_online_map);
}
}
+
+ kvm_spinlock_init();
}

/* called from main before smp_init() */
--
2.39.3