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

Tianyu Lan
2023-05-04T15:39:07Z

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.