[PATCH v4 12/15] arm64: Detect async PF para-virtualization feature

[Gavin Shan]

This implements kvm_para_available() to check if para-virtualization
features are available or not. Besides, kvm_para_has_feature() is
enhanced to detect the asynchronous page fault para-virtualization
feature. These two functions are going to be used by guest kernel
to enable the asynchronous page fault.

This also adds kernel option (CONFIG_KVM_GUEST), which is the umbrella
for the optimizations related to KVM para-virtualization.

Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
 arch/arm64/Kconfig                     | 11 +++++++++++
 arch/arm64/include/asm/kvm_para.h      | 12 +++++++++++-
 arch/arm64/include/uapi/asm/kvm_para.h |  2 ++
 3 files changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index fdcd54d39c1e..6dceae6ed7d3 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1081,6 +1081,17 @@ config PARAVIRT_TIME_ACCOUNTING
 
 	  If in doubt, say N here.
 
+config KVM_GUEST
+	bool "KVM Guest Support"
+	depends on PARAVIRT
+	default y
+	help
+	  This option enables various optimizations for running under the KVM
+	  hypervisor. Overhead for the kernel when not running inside KVM should
+	  be minimal.
+
+	  In case of doubt, say Y
+
 config KEXEC
 	depends on PM_SLEEP_SMP
 	select KEXEC_CORE
diff --git a/arch/arm64/include/asm/kvm_para.h b/arch/arm64/include/asm/kvm_para.h
index 0ea481dd1c7a..8f39c60a6619 100644
--- a/arch/arm64/include/asm/kvm_para.h
+++ b/arch/arm64/include/asm/kvm_para.h
@@ -3,6 +3,8 @@
 #define _ASM_ARM_KVM_PARA_H
 
 #include <uapi/asm/kvm_para.h>
+#include <linux/of.h>
+#include <asm/hypervisor.h>
 
 static inline bool kvm_check_and_clear_guest_paused(void)
 {
@@ -11,7 +13,12 @@ static inline bool kvm_check_and_clear_guest_paused(void)
 
 static inline unsigned int kvm_arch_para_features(void)
 {
-	return 0;
+	unsigned int features = 0;
+
+	if (kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_ASYNC_PF))
+		features |= (1 << KVM_FEATURE_ASYNC_PF);
+
+	return features;
 }
 
 static inline unsigned int kvm_arch_para_hints(void)
@@ -21,6 +28,9 @@ static inline unsigned int kvm_arch_para_hints(void)
 
 static inline bool kvm_para_available(void)
 {
+	if (IS_ENABLED(CONFIG_KVM_GUEST))
+		return true;
+
 	return false;
 }
 
diff --git a/arch/arm64/include/uapi/asm/kvm_para.h b/arch/arm64/include/uapi/asm/kvm_para.h
index 162325e2638f..70bbc7d1ec75 100644
--- a/arch/arm64/include/uapi/asm/kvm_para.h
+++ b/arch/arm64/include/uapi/asm/kvm_para.h
@@ -4,6 +4,8 @@
 
 #include <linux/types.h>
 
+#define KVM_FEATURE_ASYNC_PF		0
+
 /* Async PF */
 #define KVM_ASYNC_PF_ENABLED		(1 << 0)
 #define KVM_ASYNC_PF_SEND_ALWAYS	(1 << 1)
-- 
2.23.0