The Top-Level Functional Specification for Hyper-V, Section 3.6 [1, 2],
disallows overlapping of the input and output hypercall areas, and
hv_vtl_apicid_to_vp_id() overlaps 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

Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
---
 arch/x86/hyperv/hv_vtl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 04775346369c..ec5716960162 100644
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -189,7 +189,7 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
 	input->partition_id = HV_PARTITION_ID_SELF;
 	input->apic_ids[0] = apic_id;
 
-	output = (u32 *)input;
+	output = (u32*)*this_cpu_ptr(hyperv_pcpu_output_arg);
 
 	control = HV_HYPERCALL_REP_COMP_1 | HVCALL_GET_VP_ID_FROM_APIC_ID;
 	status = hv_do_hypercall(control, input, output);
-- 
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
> hv_vtl_apicid_to_vp_id() overlaps 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
> 
> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
> ---
>  arch/x86/hyperv/hv_vtl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 04775346369c..ec5716960162 100644
> --- a/arch/x86/hyperv/hv_vtl.c
> +++ b/arch/x86/hyperv/hv_vtl.c
> @@ -189,7 +189,7 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
>  	input->partition_id = HV_PARTITION_ID_SELF;
>  	input->apic_ids[0] = apic_id;
>  
> -	output = (u32 *)input;
> +	output = (u32*)*this_cpu_ptr(hyperv_pcpu_output_arg);
                     ^
Nit: I believe the space is preferred, but I won't insist on respinning
it for that.

It's a good idea to give credit to Michael with a Reported-by tag, and
maybe a Closes: tag with a link to his email.

As with the Fixes tag for patch 2, you don't need to respin the series
and can just reply to this thread.

Otherwise, looks good to me.

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

On 12/26/2024 2:01 PM, Easwar Hariharan wrote:
> 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
>> hv_vtl_apicid_to_vp_id() overlaps 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
>>
>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>> ---
>>   arch/x86/hyperv/hv_vtl.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
>> index 04775346369c..ec5716960162 100644
>> --- a/arch/x86/hyperv/hv_vtl.c
>> +++ b/arch/x86/hyperv/hv_vtl.c
>> @@ -189,7 +189,7 @@ static int hv_vtl_apicid_to_vp_id(u32 apic_id)
>>   	input->partition_id = HV_PARTITION_ID_SELF;
>>   	input->apic_ids[0] = apic_id;
>>   
>> -	output = (u32 *)input;
>> +	output = (u32*)*this_cpu_ptr(hyperv_pcpu_output_arg);
>                       ^
> Nit: I believe the space is preferred, but I won't insist on respinning
> it for that.
I think we can drop the whole type cast thing (as the other patch does).
Type coercion will do what is needed, and the type cast just appears to
be noise I guess.

> 
> It's a good idea to give credit to Michael with a Reported-by tag, and
> maybe a Closes: tag with a link to his email.
My bad, I should have definitely done that! Will certainly do!

> 
> As with the Fixes tag for patch 2, you don't need to respin the series
> and can just reply to this thread.
"Fixes" means something when the commit is present in the Linus'es tree
as I understood from the Wei's reply 
(https://lore.kernel.org/lkml/Z2OIsFUXcjVXpqtw@liuwe-devbox-debian-v2/):

" This commit is not in the mainline kernel yet, so this tag is not
needed.

It will most likely to be wrong since I will need to rebase the
hyperv-next branch.

I can fold this patch into the original patch and leave your
Signed-off-by there."

I'll check if the commit has been pulled into the mainline tree.

> 
> Otherwise, looks good to me.
> 
> Reviewed-by: Easwar Hariharan <eahariha@linux.microsoft.com>

-- 
Thank you,
Roman