x86/acrn: Introduce hypercall interfaces

The Service VM communicates with the hypervisor via conventional
hypercalls. VMCALL instruction is used to make the hypercalls.

ACRN hypercall ABI:
  * Hypercall number is in R8 register.
  * Up to 2 parameters are in RDI and RSI registers.
  * Return value is in RAX register.

Introduce the ACRN hypercall interfaces. Because GCC doesn't support R8
register as direct register constraints, use supported constraint as
input with a explicit MOV to R8 in beginning of asm.

Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Fengwei Yin <fengwei.yin@intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Yu Wang <yu1.wang@intel.com>
Cc: Reinette Chatre <reinette.chatre@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Originally-by: Yakui Zhao <yakui.zhao@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Shuo Liu <shuo.a.liu@intel.com>
Link: https://lore.kernel.org/r/20210207031040.49576-5-shuo.a.liu@intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/acrn.h

@@ -21,4 +21,58 @@ static inline u32 acrn_cpuid_base(void)
 	return 0;
 }
 
+/*
+ * Hypercalls for ACRN
+ *
+ * - VMCALL instruction is used to implement ACRN hypercalls.
+ * - ACRN hypercall ABI:
+ *   - Hypercall number is passed in R8 register.
+ *   - Up to 2 arguments are passed in RDI, RSI.
+ *   - Return value will be placed in RAX.
+ *
+ * Because GCC doesn't support R8 register as direct register constraints, use
+ * supported constraint as input with a explicit MOV to R8 in beginning of asm.
+ */
+static inline long acrn_hypercall0(unsigned long hcall_id)
+{
+	long result;
+
+	asm volatile("movl %1, %%r8d\n\t"
+		     "vmcall\n\t"
+		     : "=a" (result)
+		     : "g" (hcall_id)
+		     : "r8", "memory");
+
+	return result;
+}
+
+static inline long acrn_hypercall1(unsigned long hcall_id,
+				   unsigned long param1)
+{
+	long result;
+
+	asm volatile("movl %1, %%r8d\n\t"
+		     "vmcall\n\t"
+		     : "=a" (result)
+		     : "g" (hcall_id), "D" (param1)
+		     : "r8", "memory");
+
+	return result;
+}
+
+static inline long acrn_hypercall2(unsigned long hcall_id,
+				   unsigned long param1,
+				   unsigned long param2)
+{
+	long result;
+
+	asm volatile("movl %1, %%r8d\n\t"
+		     "vmcall\n\t"
+		     : "=a" (result)
+		     : "g" (hcall_id), "D" (param1), "S" (param2)
+		     : "r8", "memory");
+
+	return result;
+}
+
 #endif /* _ASM_X86_ACRN_H */