linux-kernel - RE: [PATCH hyperv-next v4 07/16] Drivers: hv: Post messages through the confidential VMBus if available

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Message-ID:
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Date: Tue, 22 Jul 2025 17:44:20 +0000
From: Michael Kelley <mhklinux@...look.com>
To: Roman Kisel <romank@...ux.microsoft.com>, "alok.a.tiwari@...cle.com"
	<alok.a.tiwari@...cle.com>, "arnd@...db.de" <arnd@...db.de>, "bp@...en8.de"
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CC: "apais@...rosoft.com" <apais@...rosoft.com>, "benhill@...rosoft.com"
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	"sunilmut@...rosoft.com" <sunilmut@...rosoft.com>
Subject: RE: [PATCH hyperv-next v4 07/16] Drivers: hv: Post messages through
 the confidential VMBus if available

From: Roman Kisel <romank@...ux.microsoft.com> Sent: Monday, July 14, 2025 3:16 PM
> 
> When the confidential VMBus is available, the guest should post
> messages to the paravisor.
> 
> Update hv_post_message() to post messages to the paravisor rather than
> through GHCB or TD calls.
> 
> Signed-off-by: Roman Kisel <romank@...ux.microsoft.com>

Reviewed-by: Michael Kelley <mhklinux@...look.com>

> ---
>  drivers/hv/hv.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
> index e9ee0177d765..816f8a14ff63 100644
> --- a/drivers/hv/hv.c
> +++ b/drivers/hv/hv.c
> @@ -74,7 +74,11 @@ int hv_post_message(union hv_connection_id connection_id,
>  	aligned_msg->payload_size = payload_size;
>  	memcpy((void *)aligned_msg->payload, payload, payload_size);
> 
> -	if (ms_hyperv.paravisor_present) {
> +	if (ms_hyperv.paravisor_present && !vmbus_is_confidential()) {
> +		/*
> +		 * If the VMBus isn't confidential, use the CoCo-specific
> +		 * mechanism to communicate with the hypervisor.
> +		 */
>  		if (hv_isolation_type_tdx())
>  			status = hv_tdx_hypercall(HVCALL_POST_MESSAGE,
>  						  virt_to_phys(aligned_msg), 0);
> @@ -85,6 +89,11 @@ int hv_post_message(union hv_connection_id connection_id,
>  		else
>  			status = HV_STATUS_INVALID_PARAMETER;
>  	} else {
> +		/*
> +		 * If there is no paravisor, this will go to the hypervisor.
> +		 * In the Confidential VMBus case, there is the paravisor
> +		 * to which this will trap.
> +		 */
>  		status = hv_do_hypercall(HVCALL_POST_MESSAGE,
>  					 aligned_msg, NULL);
>  	}
> --
> 2.43.0