[PATCH v5 1/9] mshv: Provide a way to get partition ID if running in a VMM process

[Mukesh R]

Many PCI passthru related hypercalls require partition ID of the target
guest. Guests are actually managed by MSHV driver and the partition ID
is only maintained there. Add a field in the partition struct in MSHV
driver to save the tgid of the VMM process creating the partition, and
add a function there to retrieve partition ID if the current process is
a VMM process. Furthermore, enforce one partition per VMM instance.

Signed-off-by: Mukesh R <mrathor@xxxxxxxxxxxxxxxxxxx>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@xxxxxxxxxxxxx>
---
 drivers/hv/mshv_root.h         |  1 +
 drivers/hv/mshv_root_main.c    | 33 ++++++++++++++++++++++++++++++++-
 include/asm-generic/mshyperv.h |  5 +++++
 3 files changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/mshv_root.h b/drivers/hv/mshv_root.h
index 1f086dcb7aa1..a85c24dcc701 100644
--- a/drivers/hv/mshv_root.h
+++ b/drivers/hv/mshv_root.h
@@ -138,6 +138,7 @@ struct mshv_partition {
 
 	struct mshv_girq_routing_table __rcu *pt_girq_tbl;
 	u64 isolation_type;
+	pid_t pt_vmm_tgid;
 	bool import_completed;
 	bool pt_initialized;
 #if IS_ENABLED(CONFIG_DEBUG_FS)
diff --git a/drivers/hv/mshv_root_main.c b/drivers/hv/mshv_root_main.c
index bd1359eb58dd..9b53c476bd83 100644
--- a/drivers/hv/mshv_root_main.c
+++ b/drivers/hv/mshv_root_main.c
@@ -1908,17 +1908,48 @@ mshv_partition_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+/* Given a process tgid, return partition id if it is a VMM process */
+u64 mshv_current_partid(void)
+{
+	struct mshv_partition *pt;
+	int i;
+	u64 ret_ptid = HV_PARTITION_ID_INVALID;
+
+	rcu_read_lock();
+
+	hash_for_each_rcu(mshv_root.pt_htable, i, pt, pt_hnode) {
+		if (pt->pt_vmm_tgid == current->tgid) {
+			ret_ptid = pt->pt_id;
+			break;
+		}
+	}
+
+	rcu_read_unlock();
+	return ret_ptid;
+}
+EXPORT_SYMBOL_GPL(mshv_current_partid);
+
+/* At present, we only allow one partition per VMM instance */
 static int
 add_partition(struct mshv_partition *partition)
 {
+	int rc = 0;
+
 	spin_lock(&mshv_root.pt_ht_lock);
 
+	if (mshv_current_partid() != HV_PARTITION_ID_INVALID) {
+		rc = -EEXIST;
+		goto out;
+	}
+
+	partition->pt_vmm_tgid = current->tgid;
 	hash_add_rcu(mshv_root.pt_htable, &partition->pt_hnode,
 		     partition->pt_id);
 
+out:
 	spin_unlock(&mshv_root.pt_ht_lock);
 
-	return 0;
+	return rc;
 }
 
 static_assert(MSHV_NUM_CPU_FEATURES_BANKS ==
diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h
index bf601d67cecb..e8cbc4e3f7ad 100644
--- a/include/asm-generic/mshyperv.h
+++ b/include/asm-generic/mshyperv.h
@@ -350,6 +350,7 @@ int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
 int hv_call_notify_all_processors_started(void);
 bool hv_lp_exists(u32 lp_index);
 int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
+u64 mshv_current_partid(void);
 
 #else /* CONFIG_MSHV_ROOT */
 static inline bool hv_root_partition(void) { return false; }
@@ -380,6 +381,10 @@ static inline int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u3
 {
 	return -EOPNOTSUPP;
 }
+static inline u64 mshv_current_partid(void)
+{
+	return HV_PARTITION_ID_INVALID;
+}
 #endif /* CONFIG_MSHV_ROOT */
 
 static inline int hv_deposit_memory(u64 partition_id, u64 status)
-- 
2.51.2.vfs.0.1