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Subject[PATCH v3 1/2] paravirt/locks: use new static key for controlling call of virt_spin_lock()
Date
There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" boot parameter). Today this
has the downside of falling back to unfair test and set scheme for
qspinlocks due to virt_spin_lock() detecting the virtualized
environment.

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.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
arch/x86/include/asm/qspinlock.h | 11 ++++++++++-
arch/x86/kernel/paravirt-spinlocks.c | 6 ++++++
arch/x86/kernel/smpboot.c | 2 ++
kernel/locking/qspinlock.c | 4 ++++
4 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 48a706f641f2..308dfd0714c7 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -1,6 +1,7 @@
#ifndef _ASM_X86_QSPINLOCK_H
#define _ASM_X86_QSPINLOCK_H

+#include <linux/jump_label.h>
#include <asm/cpufeature.h>
#include <asm-generic/qspinlock_types.h>
#include <asm/paravirt.h>
@@ -46,10 +47,14 @@ static inline void queued_spin_unlock(struct qspinlock *lock)
#endif

#ifdef CONFIG_PARAVIRT
+DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+void native_pv_lock_init(void) __init;
+
#define virt_spin_lock virt_spin_lock
static inline bool virt_spin_lock(struct qspinlock *lock)
{
- if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+ if (!static_branch_likely(&virt_spin_lock_key))
return false;

/*
@@ -65,6 +70,10 @@ static inline bool virt_spin_lock(struct qspinlock *lock)

return true;
}
+#else
+static inline void native_pv_lock_init(void)
+{
+}
#endif /* CONFIG_PARAVIRT */

#include <asm-generic/qspinlock.h>
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 8f2d1c9d43a8..2fc65ddea40d 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -42,3 +42,9 @@ struct pv_lock_ops pv_lock_ops = {
#endif /* SMP */
};
EXPORT_SYMBOL(pv_lock_ops);
+
+void __init native_pv_lock_init(void)
+{
+ if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+ static_branch_disable(&virt_spin_lock_key);
+}
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 54b9e89d4d6b..21500d3ba359 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -77,6 +77,7 @@
#include <asm/i8259.h>
#include <asm/realmode.h>
#include <asm/misc.h>
+#include <asm/qspinlock.h>

/* Number of siblings per CPU package */
int smp_num_siblings = 1;
@@ -1381,6 +1382,7 @@ void __init native_smp_prepare_boot_cpu(void)
/* already set me in cpu_online_mask in boot_cpu_init() */
cpumask_set_cpu(me, cpu_callout_mask);
cpu_set_state_online(me);
+ native_pv_lock_init();
}

void __init native_smp_cpus_done(unsigned int max_cpus)
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 294294c71ba4..838d235b87ef 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -76,6 +76,10 @@
#define MAX_NODES 4
#endif

+#ifdef CONFIG_PARAVIRT
+DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
+#endif
+
/*
* Per-CPU queue node structures; we can never have more than 4 nested
* contexts: task, softirq, hardirq, nmi.
--
2.12.3
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