Hyper-V: ARM64: Always use the Hyper-V hypercall interface

This patch forces the use of the Hyper-V hypercall interface,
instead of the architectural SMCCC interface on ARM64 because
not all versions of Windows support the SMCCC interface. All
versions of Windows will support the Hyper-V hypercall interface,
so this change should be both forward and backward compatible.

Signed-off-by: Sunil Muthuswamy <sunilmut@microsoft.com>

[tyhicks: Forward ported to v5.15]
Signed-off-by: Tyler Hicks <tyhicks@linux.microsoft.com>
[kms: Forward ported to v6.6]
Signed-off-by: Kelsey Steele <kelseysteele@microsoft.com>

Author: sunilmut

arch/arm64/hyperv/Makefile

@@ -1,2 +1,2 @@
 # SPDX-License-Identifier: GPL-2.0
-obj-y		:= hv_core.o mshyperv.o
+obj-y		:= hv_core.o mshyperv.o hv_hvc.o

arch/arm64/hyperv/hv_core.c

@@ -22,16 +22,13 @@
  */
 u64 hv_do_hypercall(u64 control, void *input, void *output)
 {
-	struct arm_smccc_res	res;
 	u64			input_address;
 	u64			output_address;
 
 	input_address = input ? virt_to_phys(input) : 0;
 	output_address = output ? virt_to_phys(output) : 0;
 
-	arm_smccc_1_1_hvc(HV_FUNC_ID, control,
-			  input_address, output_address, &res);
-	return res.a0;
+	return hv_do_hvc(control, input_address, output_address);
 }
 EXPORT_SYMBOL_GPL(hv_do_hypercall);
 
@@ -40,19 +37,25 @@ EXPORT_SYMBOL_GPL(hv_do_hypercall);
  * with arguments in registers instead of physical memory.
  * Avoids the overhead of virt_to_phys for simple hypercalls.
  */
-
 u64 hv_do_fast_hypercall8(u16 code, u64 input)
 {
-	struct arm_smccc_res	res;
 	u64			control;
 
 	control = (u64)code | HV_HYPERCALL_FAST_BIT;
-
-	arm_smccc_1_1_hvc(HV_FUNC_ID, control, input, &res);
-	return res.a0;
+	return hv_do_hvc(control, input);
 }
 EXPORT_SYMBOL_GPL(hv_do_fast_hypercall8);
 
+union hv_hypercall_status {
+	u64 as_uint64;
+	struct {
+		u16 status;
+		u16 reserved;
+		u16 reps_completed;  /* Low 12 bits */
+		u16 reserved2;
+	};
+};
+
 /*
  * hv_do_fast_hypercall16 -- Invoke the specified hypercall
  * with arguments in registers instead of physical memory.
@@ -75,25 +78,24 @@ EXPORT_SYMBOL_GPL(hv_do_fast_hypercall16);
  */
 void hv_set_vpreg(u32 msr, u64 value)
 {
-	struct arm_smccc_res res;
+	union hv_hypercall_status status;
 
-	arm_smccc_1_1_hvc(HV_FUNC_ID,
+	status.as_uint64 = hv_do_hvc(
 		HVCALL_SET_VP_REGISTERS | HV_HYPERCALL_FAST_BIT |
 			HV_HYPERCALL_REP_COMP_1,
 		HV_PARTITION_ID_SELF,
 		HV_VP_INDEX_SELF,
 		msr,
 		0,
 		value,
-		0,
-		&res);
+		0);
 
 	/*
 	 * Something is fundamentally broken in the hypervisor if
 	 * setting a VP register fails. There's really no way to
 	 * continue as a guest VM, so panic.
 	 */
-	BUG_ON(!hv_result_success(res.a0));
+	BUG_ON(status.status != HV_STATUS_SUCCESS);
 }
 EXPORT_SYMBOL_GPL(hv_set_vpreg);
 
@@ -106,31 +108,22 @@ EXPORT_SYMBOL_GPL(hv_set_vpreg);
 
 void hv_get_vpreg_128(u32 msr, struct hv_get_vp_registers_output *result)
 {
-	struct arm_smccc_1_2_regs args;
-	struct arm_smccc_1_2_regs res;
+	u64					status;
 
-	args.a0 = HV_FUNC_ID;
-	args.a1 = HVCALL_GET_VP_REGISTERS | HV_HYPERCALL_FAST_BIT |
-			HV_HYPERCALL_REP_COMP_1;
-	args.a2 = HV_PARTITION_ID_SELF;
-	args.a3 = HV_VP_INDEX_SELF;
-	args.a4 = msr;
-
-	/*
-	 * Use the SMCCC 1.2 interface because the results are in registers
-	 * beyond X0-X3.
-	 */
-	arm_smccc_1_2_hvc(&args, &res);
+	status = hv_do_hvc_fast_get(
+		HVCALL_GET_VP_REGISTERS | HV_HYPERCALL_FAST_BIT |
+			HV_HYPERCALL_REP_COMP_1,
+		HV_PARTITION_ID_SELF,
+		HV_VP_INDEX_SELF,
+		msr,
+		result);
 
 	/*
 	 * Something is fundamentally broken in the hypervisor if
 	 * getting a VP register fails. There's really no way to
 	 * continue as a guest VM, so panic.
 	 */
-	BUG_ON(!hv_result_success(res.a0));
-
-	result->as64.low = res.a6;
-	result->as64.high = res.a7;
+	BUG_ON((status & HV_HYPERCALL_RESULT_MASK) != HV_STATUS_SUCCESS);
 }
 EXPORT_SYMBOL_GPL(hv_get_vpreg_128);
 

arch/arm64/hyperv/hv_hvc.S

@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+/*
+ * Microsoft Hyper-V hypervisor invocation routines
+ *
+ * Copyright (C) 2018, Microsoft, Inc.
+ *
+ * Author : Michael Kelley <mikelley@microsoft.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 as published
+ * by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
+ * NON INFRINGEMENT.  See the GNU General Public License for more
+ * details.
+ */
+
+#include <linux/linkage.h>
+#include <asm/assembler.h>
+
+	.text
+/*
+ * Do the HVC instruction.  For Hyper-V the argument is always 1.
+ * x0 contains the hypercall control value, while additional registers
+ * vary depending on the hypercall, and whether the hypercall arguments
+ * are in memory or in registers (a "fast" hypercall per the Hyper-V
+ * TLFS).  When the arguments are in memory x1 is the guest physical
+ * address of the input arguments, and x2 is the guest physical
+ * address of the output arguments.  When the arguments are in
+ * registers, the register values depends on the hypercall.  Note
+ * that this version cannot return any values in registers.
+ */
+SYM_FUNC_START(hv_do_hvc)
+	hvc #1
+	ret
+SYM_FUNC_END(hv_do_hvc)
+
+/*
+ * This variant of HVC invocation is for hv_get_vpreg and
+ * hv_get_vpreg_128. The input parameters are passed in registers
+ * along with a pointer in x4 to where the output result should
+ * be stored. The output is returned in x15 and x16. x19 is used as
+ * scratch space to avoid buildng a stack frame, as Hyper-V does
+ * not preserve registers x0-x17.
+ */
+SYM_FUNC_START(hv_do_hvc_fast_get)
+	/*
+	 * Stash away x19 register so that it can be used as a scratch
+	 * register and pop it at the end.
+	 */
+	str x19, [sp, #-16]!
+	mov x19, x4
+	hvc #1
+	str x15,[x19]
+	str x16,[x19,#8]
+	ldr x19, [sp], #16
+	ret
+SYM_FUNC_END(hv_do_hvc_fast_get)

arch/arm64/include/asm/mshyperv.h

@@ -21,6 +21,10 @@
 #include <linux/arm-smccc.h>
 #include <hyperv/hvhdk.h>
 
+extern u64 hv_do_hvc(u64 control, ...);
+extern u64 hv_do_hvc_fast_get(u64 control, u64 input1, u64 input2, u64 input3,
+		struct hv_get_vp_registers_output *output);
+
 /*
  * Declare calls to get and set Hyper-V VP register values on ARM64, which
  * requires a hypercall.