[PATCH v6 06/11] x86, paravirt: Add interface to support kvm/xen vcpu preempted check

Pan Xinhui
2016-10-28T08:11:22Z

This is to fix some lock holder preemption issues. Some other locks
implementation do a spin loop before acquiring the lock itself.
Currently kernel has an interface of bool vcpu_is_preempted(int cpu). It
takes the cpu as parameter and return true if the cpu is preempted.
Then kernel can break the spin loops upon on the retval of
vcpu_is_preempted.

As kernel has used this interface, So lets support it.

To deal with kernel and kvm/xen, add vcpu_is_preempted into struct
pv_lock_ops.

Then kvm or xen could provide their own implementation to support
vcpu_is_preempted.

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
---
arch/x86/include/asm/paravirt_types.h | 2 ++
arch/x86/include/asm/spinlock.h | 8 ++++++++
arch/x86/kernel/paravirt-spinlocks.c | 6 ++++++
3 files changed, 16 insertions(+)

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 0f400c0..38c3bb7 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -310,6 +310,8 @@ struct pv_lock_ops {

void (*wait)(u8 *ptr, u8 val);
void (*kick)(int cpu);
+
+ bool (*vcpu_is_preempted)(int cpu);
};

/* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 921bea7..0526f59 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -26,6 +26,14 @@
extern struct static_key paravirt_ticketlocks_enabled;
static __always_inline bool static_key_false(struct static_key *key);

+#ifdef CONFIG_PARAVIRT_SPINLOCKS
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+ return pv_lock_ops.vcpu_is_preempted(cpu);
+}
+#endif
+
#include <asm/qspinlock.h>

/*
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 2c55a00..2f204dd 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -21,12 +21,18 @@ bool pv_is_native_spin_unlock(void)
__raw_callee_save___native_queued_spin_unlock;
}

+static bool native_vcpu_is_preempted(int cpu)
+{
+ return 0;
+}
+
struct pv_lock_ops pv_lock_ops = {
#ifdef CONFIG_SMP
.queued_spin_lock_slowpath = native_queued_spin_lock_slowpath,
.queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock),
.wait = paravirt_nop,
.kick = paravirt_nop,
+ .vcpu_is_preempted = native_vcpu_is_preempted,
#endif /* SMP */
};
EXPORT_SYMBOL(pv_lock_ops);
--
2.4.11