[PATCH 2/2] hyperv: Do not overlap the input and output hypercall areas in get_vtl(void)

[Roman Kisel <romank@linux.microsoft.com>]

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.

To fix this, enable allocation of the output hypercall pages when running in
the VTL mode and 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: 8387ce06d70b ("x86/hyperv: Set Virtual Trust Level in VMBus init message")
Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
---
 arch/x86/hyperv/hv_init.c | 2 +-
 drivers/hv/hv_common.c    | 6 +++---
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index c7185c6a290b..90c9ea00273e 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/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_get_vp_registers_output *)input;
+	output = *this_cpu_ptr(hyperv_pcpu_output_arg);
 
 	memset(input, 0, struct_size(input, names, 1));
 	input->partition_id = HV_PARTITION_ID_SELF;
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c
index c4fd07d9bf1a..5178beed6ca8 100644
--- a/drivers/hv/hv_common.c
+++ b/drivers/hv/hv_common.c
@@ -340,7 +340,7 @@ int __init hv_common_init(void)
 	BUG_ON(!hyperv_pcpu_input_arg);
 
 	/* Allocate the per-CPU state for output arg for root */
-	if (hv_root_partition) {
+	if (hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) {
 		hyperv_pcpu_output_arg = alloc_percpu(void *);
 		BUG_ON(!hyperv_pcpu_output_arg);
 	}
@@ -435,7 +435,7 @@ int hv_common_cpu_init(unsigned int cpu)
 	void **inputarg, **outputarg;
 	u64 msr_vp_index;
 	gfp_t flags;
-	int pgcount = hv_root_partition ? 2 : 1;
+	const int pgcount = (hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) ? 2 : 1;
 	void *mem;
 	int ret;
 
@@ -453,7 +453,7 @@ int hv_common_cpu_init(unsigned int cpu)
 		if (!mem)
 			return -ENOMEM;
 
-		if (hv_root_partition) {
+		if (hv_root_partition || IS_ENABLED(CONFIG_HYPERV_VTL_MODE)) {
 			outputarg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
 			*outputarg = (char *)mem + HV_HYP_PAGE_SIZE;
 		}
-- 
2.34.1