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

[Michael Kelley]

From: Nuno Das Neves <nunodasneves at 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 at linux.microsoft.com>
> Reviewed-by: Roman Kisel <romank at 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".

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