linux-kernel - [PATCH 4/6] mshv: Get the vmm capabilities offered by the hypervisor

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Message-Id: <1756428230-3599-5-git-send-email-nunodasneves@linux.microsoft.com>
Date: Thu, 28 Aug 2025 17:43:48 -0700
From: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To: linux-hyperv@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: kys@...rosoft.com,
	haiyangz@...rosoft.com,
	wei.liu@...nel.org,
	mhklinux@...look.com,
	decui@...rosoft.com,
	paekkaladevi@...ux.microsoft.com,
	Nuno Das Neves <nunodasneves@...ux.microsoft.com>
Subject: [PATCH 4/6] mshv: Get the vmm capabilities offered by the hypervisor

From: Purna Pavan Chandra Aekkaladevi <paekkaladevi@...ux.microsoft.com>

Some newer hypervisor APIs are gated by feature bits in the so-called
"vmm capabilities" partition property. Store the capabilities on
mshv_root module init, using HVCALL_GET_PARTITION_PROPERTY_EX.

Signed-off-by: Purna Pavan Chandra Aekkaladevi <paekkaladevi@...ux.microsoft.com>
Signed-off-by: Nuno Das Neves <nunodasneves@...ux.microsoft.com>
---
 drivers/hv/mshv_root.h      |  1 +
 drivers/hv/mshv_root_main.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
index 4aeb03bea6b6..0cb1e2589fe1 100644
--- a/drivers/hv/mshv_root.h
+++ b/drivers/hv/mshv_root.h
@@ -178,6 +178,7 @@ struct mshv_root {
 	struct hv_synic_pages __percpu *synic_pages;
 	spinlock_t pt_ht_lock;
 	DECLARE_HASHTABLE(pt_htable, MSHV_PARTITIONS_HASH_BITS);
+	struct hv_partition_property_vmm_capabilities vmm_caps;
 };
 
 /*
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index 56ababab57ce..29f61ecc9771 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -2327,6 +2327,28 @@ static int __init mshv_root_partition_init(struct device *dev)
 	return err;
 }
 
+static int mshv_init_vmm_caps(struct device *dev)
+{
+	int ret;
+
+	memset(&mshv_root.vmm_caps, 0, sizeof(mshv_root.vmm_caps));
+	ret = hv_call_get_partition_property_ex(HV_PARTITION_ID_SELF,
+						HV_PARTITION_PROPERTY_VMM_CAPABILITIES,
+						0, &mshv_root.vmm_caps,
+						sizeof(mshv_root.vmm_caps));
+
+	/*
+	 * HV_PARTITION_PROPERTY_VMM_CAPABILITIES is not supported in
+	 * older hyperv. Ignore the -EIO error code.
+	 */
+	if (ret && ret != -EIO)
+		return ret;
+
+	dev_dbg(dev, "vmm_caps=0x%llx\n", mshv_root.vmm_caps.as_uint64[0]);
+
+	return 0;
+}
+
 static int __init mshv_parent_partition_init(void)
 {
 	int ret;
@@ -2377,6 +2399,12 @@ static int __init mshv_parent_partition_init(void)
 	if (ret)
 		goto remove_cpu_state;
 
+	ret = mshv_init_vmm_caps(dev);
+	if (ret) {
+		dev_err(dev, "Failed to get VMM capabilities\n");
+		goto exit_partition;
+	}
+
 	ret = mshv_irqfd_wq_init();
 	if (ret)
 		goto exit_partition;
-- 
2.34.1