[RFC PATCH v4 4/4] x86/acrn: Add hypercall for ACRN guest

[Zhao Yakui <yakui.zhao@intel.com>]

When ACRN hypervisor is detected, the hypercall is needed so that the
ACRN guest can query/config some settings. For example: it can be used
to query the resources in hypervisor and manage the CPU/memory/device/
interrupt for guest operating system.

Add the hypercall so that the kernel can communicate with the low-level
ACRN hypervisor. It is implemented with vmacll instruction.

Co-developed-by: Jason Chen CJ <jason.cj.chen@intel.com>
Signed-off-by: Jason Chen CJ <jason.cj.chen@intel.com>
Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
---
V1->V2: Refine the comments for the function of acrn_hypercall0/1/2
v2->v3: Use the "vmcall" mnemonic to replace hard-code byte definition
v3->v4: refine the commit log(minor change)
---
 arch/x86/include/asm/acrn_hypercall.h | 81 +++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)
 create mode 100644 arch/x86/include/asm/acrn_hypercall.h

diff --git a/arch/x86/include/asm/acrn_hypercall.h b/arch/x86/include/asm/acrn_hypercall.h
new file mode 100644
index 0000000..30e256e
--- /dev/null
+++ b/arch/x86/include/asm/acrn_hypercall.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_X86_ACRNHYPERCALL_H
+#define _ASM_X86_ACRNHYPERCALL_H
+
+#include <linux/errno.h>
+
+#ifdef CONFIG_ACRN_GUEST
+
+/*
+ * Hypercalls for ACRN Guest
+ *
+ * Hypercall number is passed in r8 register.
+ * Return value will be placed in rax.
+ * Up to 2 arguments are passed in rdi, rsi.
+ */
+
+static inline long acrn_hypercall0(unsigned long hcall_id)
+{
+	register unsigned long r8 asm("r8") = hcall_id;
+	register long result asm("rax");
+
+	/* the hypercall is implemented with vmcall instruction.
+	 * asm volatile is used to avoid that it is dropped because of
+	 * compiler optimization.
+	 */
+	asm volatile("vmcall"
+			: "=r"(result)
+			: "r"(r8));
+
+	return result;
+}
+
+static inline long acrn_hypercall1(unsigned long hcall_id,
+				   unsigned long param1)
+{
+	register unsigned long r8 asm("r8") = hcall_id;
+	register long result asm("rax");
+
+	asm volatile("vmcall"
+			: "=r"(result)
+			: "D"(param1), "r"(r8));
+
+	return result;
+}
+
+static inline long acrn_hypercall2(unsigned long hcall_id,
+				   unsigned long param1,
+				   unsigned long param2)
+{
+	register unsigned long r8 asm("r8") = hcall_id;
+	register long result asm("rax");
+
+	asm volatile("vmcall"
+			: "=r"(result)
+			: "D"(param1), "S"(param2), "r"(r8));
+
+	return result;
+}
+
+#else
+
+static inline long acrn_hypercall0(unsigned long hcall_id)
+{
+	return -ENOTSUPP;
+}
+
+static inline long acrn_hypercall1(unsigned long hcall_id,
+				   unsigned long param1)
+{
+	return -ENOTSUPP;
+}
+
+static inline long acrn_hypercall2(unsigned long hcall_id,
+				   unsigned long param1,
+				   unsigned long param2)
+{
+	return -ENOTSUPP;
+}
+#endif /* CONFIG_ACRN_GUEST */
+#endif /* _ASM_X86_ACRNHYPERCALL_H */
-- 
2.7.4