[PATCH v2 3/4] powerpc: Reintroduce is_kvm_guest in a new avatar

[Srikar Dronamraju]

Introduce a static branch that would be set during boot if the OS
happens to be a KVM guest. Subsequent checks to see if we are on KVM
will rely on this static branch. This static branch would be used in
vcpu_is_preempted in a subsequent patch.

Cc: linuxppc-dev <linuxppc-dev@xxxxxxxxxxxxxxxx>
Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>
Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Cc: Nicholas Piggin <npiggin@xxxxxxxxx>
Cc: Nathan Lynch <nathanl@xxxxxxxxxxxxx>
Cc: Gautham R Shenoy <ego@xxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Valentin Schneider <valentin.schneider@xxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: Waiman Long <longman@xxxxxxxxxx>
Cc: Phil Auld <pauld@xxxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Signed-off-by: Srikar Dronamraju <srikar@xxxxxxxxxxxxxxxxxx>
---
 arch/powerpc/include/asm/kvm_guest.h | 10 ++++++++++
 arch/powerpc/include/asm/kvm_para.h  |  2 +-
 arch/powerpc/kernel/firmware.c       |  2 ++
 3 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
index ba8291e02ba9..627ba272e781 100644
--- a/arch/powerpc/include/asm/kvm_guest.h
+++ b/arch/powerpc/include/asm/kvm_guest.h
@@ -7,8 +7,18 @@
 #define __POWERPC_KVM_GUEST_H__
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+#include <linux/jump_label.h>
+
+DECLARE_STATIC_KEY_FALSE(kvm_guest);
+
+static inline bool is_kvm_guest(void)
+{
+	return static_branch_unlikely(&kvm_guest);
+}
+
 bool check_kvm_guest(void);
 #else
+static inline bool is_kvm_guest(void) { return false; }
 static inline bool check_kvm_guest(void) { return false; }
 #endif
 
diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
index 6fba06b6cfdb..abe1b5e82547 100644
--- a/arch/powerpc/include/asm/kvm_para.h
+++ b/arch/powerpc/include/asm/kvm_para.h
@@ -14,7 +14,7 @@
 
 static inline int kvm_para_available(void)
 {
-	return IS_ENABLED(CONFIG_KVM_GUEST) && check_kvm_guest();
+	return IS_ENABLED(CONFIG_KVM_GUEST) && is_kvm_guest();
 }
 
 static inline unsigned int kvm_arch_para_features(void)
diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
index 0aeb6a5b1a9e..28498fc573f2 100644
--- a/arch/powerpc/kernel/firmware.c
+++ b/arch/powerpc/kernel/firmware.c
@@ -22,6 +22,7 @@ EXPORT_SYMBOL_GPL(powerpc_firmware_features);
 #endif
 
 #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
+DEFINE_STATIC_KEY_FALSE(kvm_guest);
 bool check_kvm_guest(void)
 {
 	struct device_node *hyper_node;
@@ -33,6 +34,7 @@ bool check_kvm_guest(void)
 	if (!of_device_is_compatible(hyper_node, "linux,kvm"))
 		return 0;
 
+	static_branch_enable(&kvm_guest);
 	return 1;
 }
 #endif
-- 
2.18.4