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: 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 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index ba469d6b8250..cf3f7d30fcdd 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_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;
-- 
2.34.1

On 12/26/2024 1:31 PM, Roman Kisel wrote:
> 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: 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 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>

Looks good to me.

Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>