Re: [PATCH v2 2/6] Drivers: hv: Use nested hypercall for post message and signal event

[Nuno Das Neves <nunodasneves@linux.microsoft.com>]

On 7/6/2025 8:13 PM, Michael Kelley wrote:
> From: Nuno Das Neves <nunodasneves@linux.microsoft.com> Sent: Thursday, July 3, 2025 3:45 PM
>>
>> When running nested, these hypercalls must be sent to the L0 hypervisor
>> or VMBus will fail.
>>
>> Remove hv_do_nested_hypercall() and hv_do_fast_nested_hypercall8()
>> altogether and open-code these cases, since there are only 2 and all
>> they do is add the nested bit.
>>
>> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
>> Reviewed-by: Roman Kisel <romank@linux.microsoft.com>
>> ---
>>  arch/x86/include/asm/mshyperv.h | 20 --------------------
>>  drivers/hv/connection.c         |  7 +++++--
>>  drivers/hv/hv.c                 |  6 ++++--
>>  3 files changed, 9 insertions(+), 24 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
>> index 5ec92e3e2e37..e00a8431ef8e 100644
>> --- a/arch/x86/include/asm/mshyperv.h
>> +++ b/arch/x86/include/asm/mshyperv.h
>> @@ -111,12 +111,6 @@ static inline u64 hv_do_hypercall(u64 control, void *input,
>> void *output)
>>  	return hv_status;
>>  }
>>
>> -/* Hypercall to the L0 hypervisor */
>> -static inline u64 hv_do_nested_hypercall(u64 control, void *input, void *output)
>> -{
>> -	return hv_do_hypercall(control | HV_HYPERCALL_NESTED, input, output);
>> -}
>> -
>>  /* Fast hypercall with 8 bytes of input and no output */
>>  static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
>>  {
>> @@ -164,13 +158,6 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
>>  	return _hv_do_fast_hypercall8(control, input1);
>>  }
>>
>> -static inline u64 hv_do_fast_nested_hypercall8(u16 code, u64 input1)
>> -{
>> -	u64 control = (u64)code | HV_HYPERCALL_FAST_BIT | HV_HYPERCALL_NESTED;
>> -
>> -	return _hv_do_fast_hypercall8(control, input1);
>> -}
>> -
>>  /* Fast hypercall with 16 bytes of input */
>>  static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
>>  {
>> @@ -222,13 +209,6 @@ static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)
>>  	return _hv_do_fast_hypercall16(control, input1, input2);
>>  }
>>
>> -static inline u64 hv_do_fast_nested_hypercall16(u16 code, u64 input1, u64 input2)
>> -{
>> -	u64 control = (u64)code | HV_HYPERCALL_FAST_BIT | HV_HYPERCALL_NESTED;
>> -
>> -	return _hv_do_fast_hypercall16(control, input1, input2);
>> -}
>> -
>>  extern struct hv_vp_assist_page **hv_vp_assist_page;
>>
>>  static inline struct hv_vp_assist_page *hv_get_vp_assist_page(unsigned int cpu)
>> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
>> index be490c598785..47c93cee1ef6 100644
>> --- a/drivers/hv/connection.c
>> +++ b/drivers/hv/connection.c
>> @@ -518,8 +518,11 @@ void vmbus_set_event(struct vmbus_channel *channel)
>>  					 channel->sig_event, 0);
>>  		else
>>  			WARN_ON_ONCE(1);
>> -	} else {
>> -		hv_do_fast_hypercall8(HVCALL_SIGNAL_EVENT, channel->sig_event);
>> +	} else if (hv_nested) {
> 
> As coded, this won't make any hypercall for the non-nested case.
> The "else if (hv_nested)" should be just "else".

Ah, forgot to change this line. Thank you for catching it

Nuno

> 
> Michael
> 
>> +		u64 control = HVCALL_SIGNAL_EVENT;
>> +
>> +		control |= hv_nested ? HV_HYPERCALL_NESTED : 0;
>> +		hv_do_fast_hypercall8(control, channel->sig_event);
>>  	}
>>  }
>>  EXPORT_SYMBOL_GPL(vmbus_set_event);
>> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
>> index 308c8f279df8..b14c5f9e0ef2 100644
>> --- a/drivers/hv/hv.c
>> +++ b/drivers/hv/hv.c
>> @@ -85,8 +85,10 @@ int hv_post_message(union hv_connection_id connection_id,
>>  		else
>>  			status = HV_STATUS_INVALID_PARAMETER;
>>  	} else {
>> -		status = hv_do_hypercall(HVCALL_POST_MESSAGE,
>> -					 aligned_msg, NULL);
>> +		u64 control = HVCALL_POST_MESSAGE;
>> +
>> +		control |= hv_nested ? HV_HYPERCALL_NESTED : 0;
>> +		status = hv_do_hypercall(control, aligned_msg, NULL);
>>  	}
>>
>>  	local_irq_restore(flags);
>> --
>> 2.34.1