[RFC PATCH v5 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 the guest operating system.

So add the hypercall so that ACRN guest can communicate with the
low-level ACRN hypervisor. It is implemented with the VMCALL 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
v4->v5: Use _ASM_X86_ACRN_HYPERCALL_H instead of _ASM_X86_ACRNHYPERCALL_H to
align the header file of acrn_hypercall.h
        Use the "VMCALL" mnemonic in comment/commit log.
        Uppercase r8/rdi/rsi/rax for hypercall parameter registers in comment.
---
 arch/x86/include/asm/acrn_hypercall.h | 82 +++++++++++++++++++++++++++++++++++
 1 file changed, 82 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..3594436
--- /dev/null
+++ b/arch/x86/include/asm/acrn_hypercall.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _ASM_X86_ACRN_HYPERCALL_H
+#define _ASM_X86_ACRN_HYPERCALL_H
+
+#include <linux/errno.h>
+
+#ifdef CONFIG_ACRN_GUEST
+
+/*
+ * Hypercalls for ACRN guest
+ *
+ * Hypercall number is passed in R8 register.
+ * Up to 2 arguments are passed in RDI, RSI.
+ * Return value will be placed in RAX.
+ */
+
+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 the VMCALL instruction.
+	 * asm indicates that inline assembler instruction is used.
+	 * volatile qualifier is added 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_ACRN_HYPERCALL_H */
-- 
2.7.4