linux-kernel - [tip:locking/core] locking/paravirt: Use new static key for controlling call of virt_spin

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Date:   Tue, 10 Oct 2017 04:03:07 -0700
From:   tip-bot for Juergen Gross <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, hpa@...or.com, mingo@...nel.org,
        longman@...hat.com, jgross@...e.com, tglx@...utronix.de
Subject: [tip:locking/core] locking/paravirt: Use new static key for
 controlling call of virt_spin_lock()

Commit-ID:  9043442b43b1fddf202591b84702863286700c1a
Gitweb:     https://git.kernel.org/tip/9043442b43b1fddf202591b84702863286700c1a
Author:     Juergen Gross <jgross@...e.com>
AuthorDate: Wed, 6 Sep 2017 19:36:24 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Tue, 10 Oct 2017 11:50:12 +0200

locking/paravirt: Use new static key for controlling call of virt_spin_lock()

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@...e.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Waiman Long <longman@...hat.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: akataria@...are.com
Cc: boris.ostrovsky@...cle.com
Cc: chrisw@...s-sol.org
Cc: hpa@...or.com
Cc: jeremy@...p.org
Cc: rusty@...tcorp.com.au
Cc: virtualization@...ts.linux-foundation.org
Cc: xen-devel@...ts.xenproject.org
Link: http://lkml.kernel.org/r/20170906173625.18158-2-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/include/asm/qspinlock.h | 11 ++++++++++-
 arch/x86/kernel/paravirt.c       | 14 ++++++++++++--
 arch/x86/kernel/smpboot.c        |  2 ++
 3 files changed, 24 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 48a706f..308dfd0 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.c b/arch/x86/kernel/paravirt.c
index 19a3e8f..041096b 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -115,8 +115,18 @@ unsigned paravirt_patch_jmp(void *insnbuf, const void *target,
 	return 5;
 }
 
-/* Neat trick to map patch type back to the call within the
- * corresponding structure. */
+DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key);
+
+void __init native_pv_lock_init(void)
+{
+	if (!static_cpu_has(X86_FEATURE_HYPERVISOR))
+		static_branch_disable(&virt_spin_lock_key);
+}
+
+/*
+ * Neat trick to map patch type back to the call within the
+ * corresponding structure.
+ */
 static void *get_call_destination(u8 type)
 {
 	struct paravirt_patch_template tmpl = {
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index ad59edd..361f916 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;
@@ -1384,6 +1385,7 @@ 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)