Re: [RFC PATCH V5 03/15] x86/hyperv: Set Virtual Trust Level in VMBus init message

[Tianyu Lan <ltykernel@gmail.com>]

On 5/2/2023 12:30 PM, Zhi Wang wrote:
> On Mon,  1 May 2023 04:57:13 -0400
> Tianyu Lan <ltykernel@gmail.com> wrote:
> 
>> From: Tianyu Lan <tiala@microsoft.com>
>>
>> sev-snp guest provides vtl(Virtual Trust Level) and
>> get it from hyperv hvcall via HVCALL_GET_VP_REGISTERS.
>> Set target vtl in the VMBus init message.
>>
>> Signed-off-by: Tianyu Lan <tiala@microsoft.com>
>> ---
>> Change since RFC v4:
>>         * Use struct_size to calculate array size.
>>         * Fix some coding style
>>
>> Change since RFC v3:
>>         * Use the standard helper functions to check hypercall result
>>         * Fix coding style
>>
>> Change since RFC v2:
>>         * Rename get_current_vtl() to get_vtl()
>>         * Fix some coding style issues
>> ---
>>   arch/x86/hyperv/hv_init.c          | 36 ++++++++++++++++++++++++++++++
>>   arch/x86/include/asm/hyperv-tlfs.h |  7 ++++++
>>   drivers/hv/connection.c            |  1 +
>>   include/asm-generic/mshyperv.h     |  1 +
>>   include/linux/hyperv.h             |  4 ++--
>>   5 files changed, 47 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
>> index 9f3e2d71d015..331b855314b7 100644
>> --- a/arch/x86/hyperv/hv_init.c
>> +++ b/arch/x86/hyperv/hv_init.c
>> @@ -384,6 +384,40 @@ static void __init hv_get_partition_id(void)
>>   	local_irq_restore(flags);
>>   }
>>   
>> +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;
>> +	u64 vtl = 0;
>> +	u64 ret;
>> +	unsigned long flags;
>> +
>> +	local_irq_save(flags);
>> +	input = *this_cpu_ptr(hyperv_pcpu_input_arg);
>> +	output = (struct hv_get_vp_registers_output *)input;
> 
> ===
>> +	if (!input) {
>> +		local_irq_restore(flags);
>> +		goto done;
>> +	}
>> +
> ===
> Is this really necessary?
> 
> drivers/hv/hv_common.c:
> 
>          hyperv_pcpu_input_arg = alloc_percpu(void  *);
>          BUG_ON(!hyperv_pcpu_input_arg);
> 
> 

Hi Zhi:
	The hyperv_pcpu_input_arg is a point to address of input arg
pages and these pages are allocated in the hv_common_cpu_init(). If
it failed to allocate these pages, the value pointed by 
hyperv_pcpu_input_arg will be NULL.