[PATCH v2 14/17] 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 <gs...@redhat.com>
---
 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 f39568b28ec1..792ae09aa690 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -1078,6 +1078,17 @@ 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