[PATCH v4 4/6] LoongArch: Add paravirt interface for guest kernel

[Bibo Mao]

The patch adds paravirt interface for guest kernel, function
pv_guest_initi() firstly checks whether system runs on VM mode. If kernel
runs on VM mode, it will call function kvm_para_available() to detect
whether current VMM is KVM hypervisor. And the paravirt function can work
only if current VMM is KVM hypervisor, since there is only KVM hypervisor
supported on LoongArch now.

This patch only adds paravirt interface for guest kernel, however there
is not effective pv functions added here.

Signed-off-by: Bibo Mao <maobibo@xxxxxxxxxxx>
---
 arch/loongarch/Kconfig                        |  9 ++++
 arch/loongarch/include/asm/kvm_para.h         |  7 ++++
 arch/loongarch/include/asm/paravirt.h         | 27 ++++++++++++
 .../include/asm/paravirt_api_clock.h          |  1 +
 arch/loongarch/kernel/Makefile                |  1 +
 arch/loongarch/kernel/paravirt.c              | 41 +++++++++++++++++++
 arch/loongarch/kernel/setup.c                 |  2 +
 7 files changed, 88 insertions(+)
 create mode 100644 arch/loongarch/include/asm/paravirt.h
 create mode 100644 arch/loongarch/include/asm/paravirt_api_clock.h
 create mode 100644 arch/loongarch/kernel/paravirt.c

diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 10959e6c3583..817a56dff80f 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -585,6 +585,15 @@ config CPU_HAS_PREFETCH
 	bool
 	default y
 
+config PARAVIRT
+	bool "Enable paravirtualization code"
+	depends on AS_HAS_LVZ_EXTENSION
+	help
+          This changes the kernel so it can modify itself when it is run
+	  under a hypervisor, potentially improving performance significantly
+	  over full virtualization.  However, when run without a hypervisor
+	  the kernel is theoretically slower and slightly larger.
+
 config ARCH_SUPPORTS_KEXEC
 	def_bool y
 
diff --git a/arch/loongarch/include/asm/kvm_para.h b/arch/loongarch/include/asm/kvm_para.h
index 9425d3b7e486..41200e922a82 100644
--- a/arch/loongarch/include/asm/kvm_para.h
+++ b/arch/loongarch/include/asm/kvm_para.h
@@ -2,6 +2,13 @@
 #ifndef _ASM_LOONGARCH_KVM_PARA_H
 #define _ASM_LOONGARCH_KVM_PARA_H
 
+/*
+ * Hypcall code field
+ */
+#define HYPERVISOR_KVM			1
+#define HYPERVISOR_VENDOR_SHIFT		8
+#define HYPERCALL_CODE(vendor, code)	((vendor << HYPERVISOR_VENDOR_SHIFT) + code)
+
 /*
  * LoongArch hypcall return code
  */
diff --git a/arch/loongarch/include/asm/paravirt.h b/arch/loongarch/include/asm/paravirt.h
new file mode 100644
index 000000000000..b64813592ba0
--- /dev/null
+++ b/arch/loongarch/include/asm/paravirt.h
@@ -0,0 +1,27 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_LOONGARCH_PARAVIRT_H
+#define _ASM_LOONGARCH_PARAVIRT_H
+
+#ifdef CONFIG_PARAVIRT
+#include <linux/static_call_types.h>
+struct static_key;
+extern struct static_key paravirt_steal_enabled;
+extern struct static_key paravirt_steal_rq_enabled;
+
+u64 dummy_steal_clock(int cpu);
+DECLARE_STATIC_CALL(pv_steal_clock, dummy_steal_clock);
+
+static inline u64 paravirt_steal_clock(int cpu)
+{
+	return static_call(pv_steal_clock)(cpu);
+}
+
+int pv_guest_init(void);
+#else
+static inline int pv_guest_init(void)
+{
+	return 0;
+}
+
+#endif // CONFIG_PARAVIRT
+#endif
diff --git a/arch/loongarch/include/asm/paravirt_api_clock.h b/arch/loongarch/include/asm/paravirt_api_clock.h
new file mode 100644
index 000000000000..65ac7cee0dad
--- /dev/null
+++ b/arch/loongarch/include/asm/paravirt_api_clock.h
@@ -0,0 +1 @@
+#include <asm/paravirt.h>
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 3c808c680370..662e6e9de12d 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -48,6 +48,7 @@ obj-$(CONFIG_MODULES)		+= module.o module-sections.o
 obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 
 obj-$(CONFIG_PROC_FS)		+= proc.o
+obj-$(CONFIG_PARAVIRT)		+= paravirt.o
 
 obj-$(CONFIG_SMP)		+= smp.o
 
diff --git a/arch/loongarch/kernel/paravirt.c b/arch/loongarch/kernel/paravirt.c
new file mode 100644
index 000000000000..21d01d05791a
--- /dev/null
+++ b/arch/loongarch/kernel/paravirt.c
@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/export.h>
+#include <linux/types.h>
+#include <linux/jump_label.h>
+#include <linux/kvm_para.h>
+#include <asm/paravirt.h>
+#include <linux/static_call.h>
+
+struct static_key paravirt_steal_enabled;
+struct static_key paravirt_steal_rq_enabled;
+
+static u64 native_steal_clock(int cpu)
+{
+	return 0;
+}
+
+DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
+
+static bool kvm_para_available(void)
+{
+	static int hypervisor_type;
+	int config;
+
+	if (!hypervisor_type) {
+		config = read_cpucfg(CPUCFG_KVM_SIG);
+		if (!memcmp(&config, KVM_SIGNATURE, 4))
+			hypervisor_type = HYPERVISOR_KVM;
+	}
+
+	return hypervisor_type == HYPERVISOR_KVM;
+}
+
+int __init pv_guest_init(void)
+{
+	if (!cpu_has_hypervisor)
+		return 0;
+	if (!kvm_para_available())
+		return 0;
+
+	return 1;
+}
diff --git a/arch/loongarch/kernel/setup.c b/arch/loongarch/kernel/setup.c
index edf2bba80130..de5c36dccc49 100644
--- a/arch/loongarch/kernel/setup.c
+++ b/arch/loongarch/kernel/setup.c
@@ -43,6 +43,7 @@
 #include <asm/efi.h>
 #include <asm/loongson.h>
 #include <asm/numa.h>
+#include <asm/paravirt.h>
 #include <asm/pgalloc.h>
 #include <asm/sections.h>
 #include <asm/setup.h>
@@ -367,6 +368,7 @@ void __init platform_init(void)
 	pr_info("The BIOS Version: %s\n", b_info.bios_version);
 
 	efi_runtime_init();
+	pv_guest_init();
 }
 
 static void __init check_kernel_sections_mem(void)
-- 
2.39.3