Avoid raising and lowering the IRQL if not needed (#4007)

* Avoid raising and lowering the IRQL if not needed Signed-off-by: Alan Jowett <[email protected]> * PR feedback Signed-off-by: Alan Jowett <[email protected]> --------- Signed-off-by: Alan Jowett <[email protected]> Co-authored-by: Alan Jowett <[email protected]>
microsoft · Nov 13, 2024 · 3bdeb43 · 3bdeb43
1 parent 50df22f
commit 3bdeb43
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Showing 3 changed files with 37 additions and 5 deletions.
diff --git a/libs/execution_context/ebpf_maps.c b/libs/execution_context/ebpf_maps.c
@@ -1177,10 +1177,9 @@ _Requires_lock_held_(map->partitions[partition].lock) static void _merge_hot_int
 static void
 _insert_into_hot_list(_Inout_ ebpf_core_lru_map_t* map, size_t partition, _Inout_ ebpf_lru_entry_t* entry)
 {
-    bool lock_held = false;
-
     ebpf_lru_key_state_t key_state = _get_key_state(map, partition, entry);
     ebpf_lock_state_t state = 0;
+    bool is_preemptible = ebpf_is_preemptible();
 
     switch (key_state) {
     case EBPF_LRU_KEY_UNINITIALIZED:
@@ -1193,8 +1192,11 @@ _insert_into_hot_list(_Inout_ ebpf_core_lru_map_t* map, size_t partition, _Inout
         return;
     }
 
-    state = ebpf_lock_lock(&map->partitions[partition].lock);
-    lock_held = true;
+    if (!is_preemptible) {
+        ebpf_lock_lock_at_dispatch(&map->partitions[partition].lock);
+    } else {
+        state = ebpf_lock_lock(&map->partitions[partition].lock);
+    }
 
     key_state = _get_key_state(map, partition, entry);
 
@@ -1223,7 +1225,9 @@ _insert_into_hot_list(_Inout_ ebpf_core_lru_map_t* map, size_t partition, _Inout
 
     _merge_hot_into_cold_list_if_needed(map, partition);
 
-    if (lock_held) {
+    if (!is_preemptible) {
+        ebpf_lock_unlock_at_dispatch(&map->partitions[partition].lock);
+    } else {
         ebpf_lock_unlock(&map->partitions[partition].lock, state);
     }
 }

diff --git a/libs/runtime/ebpf_platform.c b/libs/runtime/ebpf_platform.c
@@ -52,6 +52,18 @@ _Requires_lock_held_(*lock) _Releases_lock_(*lock) _IRQL_requires_(DISPATCH_LEVE
     KeReleaseSpinLock(lock, state);
 }
 
+_Requires_lock_not_held_(*lock) _Acquires_lock_(*lock) _IRQL_requires_max_(DISPATCH_LEVEL)
+    _IRQL_requires_(DISPATCH_LEVEL) void ebpf_lock_lock_at_dispatch(_Inout_ ebpf_lock_t* lock)
+{
+    KeAcquireSpinLockAtDpcLevel(lock);
+}
+
+_Requires_lock_held_(*lock) _Releases_lock_(*lock)
+    _IRQL_requires_(DISPATCH_LEVEL) void ebpf_lock_unlock_at_dispatch(_Inout_ ebpf_lock_t* lock)
+{
+    KeReleaseSpinLockFromDpcLevel(lock);
+}
+
 bool
 ebpf_is_preemptible()
 {

diff --git a/libs/runtime/ebpf_platform.h b/libs/runtime/ebpf_platform.h
@@ -223,6 +223,22 @@ extern "C"
     _Requires_lock_held_(*lock) _Releases_lock_(*lock) _IRQL_requires_(DISPATCH_LEVEL) void ebpf_lock_unlock(
         _Inout_ ebpf_lock_t* lock, _IRQL_restores_ ebpf_lock_state_t state);
 
+    /**
+     * @brief Acquire exclusive access to the lock.
+     * @param[in, out] lock Pointer to memory location that contains the lock.
+     * @returns The previous lock_state required for unlock.
+     */
+    _Requires_lock_not_held_(*lock) _Acquires_lock_(*lock) _IRQL_requires_(DISPATCH_LEVEL)
+        _IRQL_requires_max_(DISPATCH_LEVEL) void ebpf_lock_lock_at_dispatch(_Inout_ ebpf_lock_t* lock);
+
+    /**
+     * @brief Release exclusive access to the lock.
+     * @param[in, out] lock Pointer to memory location that contains the lock.
+     * @param[in] state The state returned from ebpf_lock_lock.
+     */
+    _Requires_lock_held_(*lock) _Releases_lock_(*lock)
+        _IRQL_requires_(DISPATCH_LEVEL) void ebpf_lock_unlock_at_dispatch(_Inout_ ebpf_lock_t* lock);
+
     /**
      * @brief Raise the IRQL to new_irql.
      *