hyperv: Do not overlap the hvcall IO areas in get_vtl()

The Top-Level Functional Specification for Hyper-V, Section 3.6 [1, 2],
disallows overlapping of the input and output hypercall areas, and
get_vtl(void) does overlap them.

Use the output hypercall page of the current vCPU for the hypercall.

[1] https://learn.microsoft.com/en-us/virtualization/hyper-v-on-windows/tlfs/hypercall-interface
[2] https://github.com/MicrosoftDocs/Virtualization-Documentation/tree/main/tlfs

Fixes: 8387ce0 ("x86/hyperv: Set Virtual Trust Level in VMBus init message")
Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250108222138.1623703-5-romank@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250108222138.1623703-5-romank@linux.microsoft.com>

arch/x86/hyperv/hv_init.c

@@ -422,7 +422,7 @@ static u8 __init get_vtl(void)
 
 	local_irq_save(flags);
 	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
-	output = (struct hv_output_get_vp_registers *)input;
+	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
 
 	memset(input, 0, struct_size(input, names, 1));
 	input->partition_id = HV_PARTITION_ID_SELF;