linux-kernel - [PATCH hyperv-next v5 07/16] Drivers: hv: Post messages through the confidential VMBus if available

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Message-ID: <20250828010557.123869-8-romank@linux.microsoft.com>
Date: Wed, 27 Aug 2025 18:05:48 -0700
From: Roman Kisel <romank@...ux.microsoft.com>
To: arnd@...db.de,
	bp@...en8.de,
	corbet@....net,
	dave.hansen@...ux.intel.com,
	decui@...rosoft.com,
	haiyangz@...rosoft.com,
	hpa@...or.com,
	kys@...rosoft.com,
	mikelley@...rosoft.com,
	mingo@...hat.com,
	tglx@...utronix.de,
	Tianyu.Lan@...rosoft.com,
	wei.liu@...nel.org,
	x86@...nel.org,
	linux-hyperv@...r.kernel.org,
	linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Cc: benhill@...rosoft.com,
	bperkins@...rosoft.com,
	sunilmut@...rosoft.com,
	romank@...ux.microsoft.com
Subject: [PATCH hyperv-next v5 07/16] Drivers: hv: Post messages through the confidential VMBus if available

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: Tianyu Lan <tiala@...rosoft.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 fe97591bc44d..951330ca4ba9 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -76,7 +76,11 @@ 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);
@@ -90,6 +94,11 @@ int hv_post_message(union hv_connection_id connection_id,
 		u64 control = HVCALL_POST_MESSAGE;
 
 		control |= hv_nested ? HV_HYPERCALL_NESTED : 0;
+		/*
+		 * 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(control, aligned_msg, NULL);
 	}
 
-- 
2.43.0