[PATCH v4 1/2] drivers/hv: introduce vmbus_channel_set_cpu()

Hamza Mahfooz
2025-01-16T13:41:50Z

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>
---
v2: separate vmbus_channel_set_cpu() changes from
cpu offlining changes.

v3: address comments from Michael.
---
drivers/hv/vmbus_drv.c | 50 +++++++++++++++++++++++++-----------------
include/linux/hyperv.h | 1 +
2 files changed, 31 insertions(+), 20 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 2892b8da20a5..0ca0e85e6edd 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;
}

/*
@@ -1708,9 +1702,25 @@ 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)
+{
+ ssize_t ret = count;
+ u32 target_cpu;
+
+ 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;
}
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 02a226bcf0ed..25e9e982f1b0 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1670,6 +1670,7 @@ 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 *
--
2.47.1