Merge tag 'hyperv-next-signed-20250324' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux

Pull hyperv updates from Wei Liu:

 - Add support for running as the root partition in Hyper-V (Microsoft
   Hypervisor) by exposing /dev/mshv (Nuno and various people)

 - Add support for CPU offlining in Hyper-V (Hamza Mahfooz)

 - Misc fixes and cleanups (Roman Kisel, Tianyu Lan, Wei Liu, Michael
   Kelley, Thorsten Blum)

* tag 'hyperv-next-signed-20250324' of git://git.kernel.org/pub/scm/linux/kernel/git/hyperv/linux: (24 commits)
  x86/hyperv: fix an indentation issue in mshyperv.h
  x86/hyperv: Add comments about hv_vpset and var size hypercall input args
  Drivers: hv: Introduce mshv_root module to expose /dev/mshv to VMMs
  hyperv: Add definitions for root partition driver to hv headers
  x86: hyperv: Add mshv_handler() irq handler and setup function
  Drivers: hv: Introduce per-cpu event ring tail
  Drivers: hv: Export some functions for use by root partition module
  acpi: numa: Export node_to_pxm()
  hyperv: Introduce hv_recommend_using_aeoi()
  arm64/hyperv: Add some missing functions to arm64
  x86/mshyperv: Add support for extended Hyper-V features
  hyperv: Log hypercall status codes as strings
  x86/hyperv: Fix check of return value from snp_set_vmsa()
  x86/hyperv: Add VTL mode callback for restarting the system
  x86/hyperv: Add VTL mode emergency restart callback
  hyperv: Remove unused union and structs
  hyperv: Add CONFIG_MSHV_ROOT to gate root partition support
  hyperv: Change hv_root_partition into a function
  hyperv: Convert hypercall statuses to linux error codes
  drivers/hv: add CPU offlining support
  ...

1 files changed, 32 insertions, 22 deletions

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 6e55a1a2613d..8d3cff42bdbb 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1611,16 +1611,16 @@ static ssize_t target_cpu_show(struct vmbus_channel *channel, char *buf)
 {
 	return sprintf(buf, "%u\n", channel->target_cpu);
 }
-static ssize_t target_cpu_store(struct vmbus_channel *channel,
-				const char *buf, size_t count)
+
+int vmbus_channel_set_cpu(struct vmbus_channel *channel, u32 target_cpu)
 {
-	u32 target_cpu, origin_cpu;
-	ssize_t ret = count;
+	u32 origin_cpu;
+	int ret = 0;
 
-	if (vmbus_proto_version < VERSION_WIN10_V4_1)
-		return -EIO;
+	lockdep_assert_cpus_held();
+	lockdep_assert_held(&vmbus_connection.channel_mutex);
 
-	if (sscanf(buf, "%uu", &target_cpu) != 1)
+	if (vmbus_proto_version < VERSION_WIN10_V4_1)
 		return -EIO;
 
 	/* Validate target_cpu for the cpumask_test_cpu() operation below. */
@@ -1630,22 +1630,17 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 	if (!cpumask_test_cpu(target_cpu, housekeeping_cpumask(HK_TYPE_MANAGED_IRQ)))
 		return -EINVAL;
 
-	/* No CPUs should come up or down during this. */
-	cpus_read_lock();
-
-	if (!cpu_online(target_cpu)) {
-		cpus_read_unlock();
+	if (!cpu_online(target_cpu))
 		return -EINVAL;
-	}
 
 	/*
-	 * Synchronizes target_cpu_store() and channel closure:
+	 * Synchronizes vmbus_channel_set_cpu() and channel closure:
 	 *
 	 * { Initially: state = CHANNEL_OPENED }
 	 *
 	 * CPU1				CPU2
 	 *
-	 * [target_cpu_store()]		[vmbus_disconnect_ring()]
+	 * [vmbus_channel_set_cpu()]	[vmbus_disconnect_ring()]
 	 *
 	 * LOCK channel_mutex		LOCK channel_mutex
 	 * LOAD r1 = state		LOAD r2 = state
@@ -1660,7 +1655,6 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 	 * Note.  The host processes the channel messages "sequentially", in
 	 * the order in which they are received on a per-partition basis.
 	 */
-	mutex_lock(&vmbus_connection.channel_mutex);
 
 	/*
 	 * Hyper-V will ignore MODIFYCHANNEL messages for "non-open" channels;
@@ -1668,17 +1662,17 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 	 */
 	if (channel->state != CHANNEL_OPENED_STATE) {
 		ret = -EIO;
-		goto cpu_store_unlock;
+		goto end;
 	}
 
 	origin_cpu = channel->target_cpu;
 	if (target_cpu == origin_cpu)
-		goto cpu_store_unlock;
+		goto end;
 
 	if (vmbus_send_modifychannel(channel,
 				     hv_cpu_number_to_vp_number(target_cpu))) {
 		ret = -EIO;
-		goto cpu_store_unlock;
+		goto end;
 	}
 
 	/*
@@ -1708,10 +1702,26 @@ static ssize_t target_cpu_store(struct vmbus_channel *channel,
 				origin_cpu, target_cpu);
 	}
 
-cpu_store_unlock:
+end:
+	return ret;
+}
+
+static ssize_t target_cpu_store(struct vmbus_channel *channel,
+				const char *buf, size_t count)
+{
+	u32 target_cpu;
+	ssize_t ret;
+
+	if (sscanf(buf, "%uu", &target_cpu) != 1)
+		return -EIO;
+
+	cpus_read_lock();
+	mutex_lock(&vmbus_connection.channel_mutex);
+	ret = vmbus_channel_set_cpu(channel, target_cpu);
 	mutex_unlock(&vmbus_connection.channel_mutex);
 	cpus_read_unlock();
-	return ret;
+
+	return ret ?: count;
 }
 static VMBUS_CHAN_ATTR(cpu, 0644, target_cpu_show, target_cpu_store);
 
@@ -2659,7 +2669,7 @@ static int __init hv_acpi_init(void)
 	if (!hv_is_hyperv_initialized())
 		return -ENODEV;
 
-	if (hv_root_partition && !hv_nested)
+	if (hv_root_partition() && !hv_nested)
 		return 0;
 
 	/*