[PATCH v2 3/6] drivers/hv: arch-neutral implementation of get_vtl()

[Roman Kisel]

To run in the VTL mode, Hyper-V drivers have to know what
VTL the system boots in, and the arm64/hyperv code does not
have the means to compute that.

Refactor the code to hoist the function that detects VTL,
make it arch-neutral to be able to employ it to get the VTL
on arm64.

Signed-off-by: Roman Kisel <romank at linux.microsoft.com>
---
 arch/x86/hyperv/hv_init.c          | 34 -----------------------
 arch/x86/include/asm/hyperv-tlfs.h |  7 -----
 drivers/hv/hv_common.c             | 43 ++++++++++++++++++++++++++++++
 include/asm-generic/hyperv-tlfs.h  |  7 +++++
 include/asm-generic/mshyperv.h     |  6 +++++
 5 files changed, 56 insertions(+), 41 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 17a71e92a343..c350fa05ee59 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -413,40 +413,6 @@ static void __init hv_get_partition_id(void)
 	local_irq_restore(flags);
 }
 
-#if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
-static u8 __init get_vtl(void)
-{
-	u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS;
-	struct hv_get_vp_registers_input *input;
-	struct hv_get_vp_registers_output *output;
-	unsigned long flags;
-	u64 ret;
-
-	local_irq_save(flags);
-	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
-	output = (struct hv_get_vp_registers_output *)input;
-
-	memset(input, 0, struct_size(input, element, 1));
-	input->header.partitionid = HV_PARTITION_ID_SELF;
-	input->header.vpindex = HV_VP_INDEX_SELF;
-	input->header.inputvtl = 0;
-	input->element[0].name0 = HV_X64_REGISTER_VSM_VP_STATUS;
-
-	ret = hv_do_hypercall(control, input, output);
-	if (hv_result_success(ret)) {
-		ret = output->as64.low & HV_X64_VTL_MASK;
-	} else {
-		pr_err("Failed to get VTL(error: %lld) exiting...\n", ret);
-		BUG();
-	}
-
-	local_irq_restore(flags);
-	return ret;
-}
-#else
-static inline u8 get_vtl(void) { return 0; }
-#endif
-
 /*
  * This function is to be invoked early in the boot sequence after the
  * hypervisor has been detected.
diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
index 3787d26810c1..9ee68eb8e6ff 100644
--- a/arch/x86/include/asm/hyperv-tlfs.h
+++ b/arch/x86/include/asm/hyperv-tlfs.h
@@ -309,13 +309,6 @@ enum hv_isolation_type {
 #define HV_MSR_STIMER0_CONFIG	(HV_X64_MSR_STIMER0_CONFIG)
 #define HV_MSR_STIMER0_COUNT	(HV_X64_MSR_STIMER0_COUNT)
 
-/*
- * Registers are only accessible via HVCALL_GET_VP_REGISTERS hvcall and
- * there is not associated MSR address.
- */
-#define	HV_X64_REGISTER_VSM_VP_STATUS	0x000D0003
-#define	HV_X64_VTL_MASK			GENMASK(3, 0)
-
 /* Hyper-V memory host visibility */
 enum hv_mem_host_visibility {
 	VMBUS_PAGE_NOT_VISIBLE		= 0,
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index dde3f9b6871a..d4cf477a4d0c 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -660,3 +660,46 @@ u64 __weak hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
 	return HV_STATUS_INVALID_PARAMETER;
 }
 EXPORT_SYMBOL_GPL(hv_tdx_hypercall);
+
+#if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
+u8 __init get_vtl(void)
+{
+	u64 control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_REGISTERS;
+	struct hv_get_vp_registers_input *input;
+	struct hv_get_vp_registers_output *output;
+	unsigned long flags;
+	u64 ret;
+
+	local_irq_save(flags);
+	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
+	output = (struct hv_get_vp_registers_output *)input;
+
+	memset(input, 0, struct_size(input, element, 1));
+	input->header.partitionid = HV_PARTITION_ID_SELF;
+	input->header.vpindex = HV_VP_INDEX_SELF;
+	input->header.inputvtl = 0;
+	input->element[0].name0 = HV_REGISTER_VSM_VP_STATUS;
+
+	ret = hv_do_hypercall(control, input, output);
+	if (hv_result_success(ret)) {
+		ret = output->as64.low & HV_VTL_MASK;
+	} else {
+		pr_err("Failed to get VTL(error: %lld) exiting...\n", ret);
+
+		/*
+		 * This is a dead end, something fundamental is broken.
+		 *
+		 * There is no sensible way of continuing as the Hyper-V drivers
+		 * transitively depend via the vmbus driver on knowing which VTL
+		 * they run in to establish communication with the host. The kernel
+		 * is going to be worse off if continued booting than a panicked one,
+		 * just hung and stuck, producing second-order failures, with neither
+		 * a way to recover nor to provide expected services.
+		 */
+		BUG();
+	}
+
+	local_irq_restore(flags);
+	return ret;
+}
+#endif
diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
index 87e3d49a4e29..682bcda3124f 100644
--- a/include/asm-generic/hyperv-tlfs.h
+++ b/include/asm-generic/hyperv-tlfs.h
@@ -75,6 +75,13 @@
 /* AccessTscInvariantControls privilege */
 #define HV_ACCESS_TSC_INVARIANT			BIT(15)
 
+/*
+ * This synthetic register is only accessible via the HVCALL_GET_VP_REGISTERS
+ * hvcall, and there is no an associated MSR on x86.
+ */
+#define	HV_REGISTER_VSM_VP_STATUS	0x000D0003
+#define	HV_VTL_MASK			GENMASK(3, 0)
+
 /*
  * Group B features.
  */
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index 99935779682d..ea434186d765 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -301,4 +301,10 @@ static inline enum hv_isolation_type hv_get_isolation_type(void)
 }
 #endif /* CONFIG_HYPERV */
 
+#if IS_ENABLED(CONFIG_HYPERV_VTL_MODE)
+u8 __init get_vtl(void);
+#else
+static inline u8 get_vtl(void) { return 0; }
+#endif
+
 #endif
-- 
2.45.0