drivers/hv: introduce vmbus_channel_set_cpu()

The core functionality in target_cpu_store() is also needed in a
subsequent patch for automatically changing the CPU when taking
a CPU offline. As such, factor out the body of target_cpu_store()
into new function vmbus_channel_set_cpu() that can also be used
elsewhere.

No functional change is intended.

Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Michael Kelley <mhklinux@outlook.com>
Cc: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/20250117203309.192072-2-hamzamahfooz@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Message-ID: <20250117203309.192072-2-hamzamahfooz@linux.microsoft.com>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 0f6cd44fff292158d6fb421f37cd2d0ca596c1f1..75eb1390b45cae94a6dc0c283bf2d628044861e4 100644 (file)
--- 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);
 

diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 4179add2864b41fb8aa81471d205f969eda29673..7f4f8d8bdf4322f3b16650478653cff55479a9c1 100644 (file)
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1661,6 +1661,7 @@ int vmbus_send_tl_connect_request(const guid_t *shv_guest_servie_id,
                                  const guid_t *shv_host_servie_id);
 int vmbus_send_modifychannel(struct vmbus_channel *channel, u32 target_vp);
 void vmbus_set_event(struct vmbus_channel *channel);
+int vmbus_channel_set_cpu(struct vmbus_channel *channel, u32 target_cpu);
 
 /* Get the start of the ring buffer. */
 static inline void *