Re: [PATCH 3/4] paravirt: add virt_spin_lock pvops function

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.

Make virt_spin_lock() a paravirt operation in order to enable users
to select an explicit behavior like bare metal.

Signed-off-by: Juergen Gross <jgross@suse.com>
---
 arch/x86/include/asm/paravirt.h       |  5 ++++
 arch/x86/include/asm/paravirt_types.h |  1 +
 arch/x86/include/asm/qspinlock.h      | 48 ++++++++++++++++++++++++-----------
 arch/x86/kernel/paravirt-spinlocks.c  | 14 ++++++++++
 arch/x86/kernel/smpboot.c             |  2 ++
 5 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index c25dd22f7c70..d9e954fb37df 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h

@@ -725,6 +725,11 @@ static __always_inline bool pv_vcpu_is_preempted(long cpu)
 	return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu);
 }
 
+static __always_inline bool pv_virt_spin_lock(struct qspinlock *lock)
+{
+	return PVOP_CALLEE1(bool, pv_lock_ops.virt_spin_lock, lock);
+}
+
 #endif /* SMP && PARAVIRT_SPINLOCKS */
 
 #ifdef CONFIG_X86_32

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 19efefc0e27e..928f5e7953a7 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h

@@ -319,6 +319,7 @@ struct pv_lock_ops {
 	void (*kick)(int cpu);
 
 	struct paravirt_callee_save vcpu_is_preempted;
+	struct paravirt_callee_save virt_spin_lock;
 } __no_randomize_layout;
 
 /* This contains all the paravirt structures: we get a convenient

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 48a706f641f2..fbd98896385c 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h

@@ -17,6 +17,25 @@ static inline void native_queued_spin_unlock(struct qspinlock *lock)
 	smp_store_release((u8 *)lock, 0);
 }
 
+static inline bool native_virt_spin_lock(struct qspinlock *lock)
+{
+	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+		return false;
+