[PATCH][v2] x86/sgx: Use list_for_each_entry_srcu() for mm_list traversal

From: Li RongQing <[email protected]>

In commit 1728ab54b4be ("x86/sgx: Add a page reclaimer") (v5.11),
list_for_each_entry_rcu() was used to traverse the enclave's mm_list.
However, this is incorrect because the list is protected by a Sleepable
RCU (SRCU) lock (encl->srcu).

Since commit 28875945ba98 ("rcu: Add support for consolidated-RCU reader
checking") (v5.4), RCU lockdep checking has become stricter. When
CONFIG_PROVE_RCU is enabled, using the standard list_for_each_entry_rcu()
while only holding an SRCU lock triggers "suspicious RCU usage" false
positive warnings, as it does not recognize SRCU read-side critical
sections.

Fix this by switching to list_for_each_entry_srcu(), which was
introduced specifically for this purpose in commit ae2212a7216b
("rculist: Introduce list/hlist_for_each_entry_srcu() macros") (v5.10).
This correctly associates the traversal with the SRCU lock and
eliminates the lockdep warnings.

Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
Signed-off-by: Li RongQing <[email protected]>
Acked-by: Kai Huang <[email protected]>
---
Diff with v1: rewrite changelog

 arch/x86/kernel/cpu/sgx/encl.c | 12 ++++++++----
 arch/x86/kernel/cpu/sgx/main.c |  3 ++-
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
index ac60ebd..91362d7 100644
--- a/arch/x86/kernel/cpu/sgx/encl.c
+++ b/arch/x86/kernel/cpu/sgx/encl.c
@@ -822,7 +822,8 @@ static struct sgx_encl_mm *sgx_encl_find_mm(struct sgx_encl *encl,
 
 	idx = srcu_read_lock(&encl->srcu);
 
-	list_for_each_entry_rcu(tmp, &encl->mm_list, list) {
+	list_for_each_entry_srcu(tmp, &encl->mm_list, list,
+			srcu_read_lock_held(&encl->srcu)) {
 		if (tmp->mm == mm) {
 			encl_mm = tmp;
 			break;
@@ -933,7 +934,8 @@ const cpumask_t *sgx_encl_cpumask(struct sgx_encl *encl)
 
 	idx = srcu_read_lock(&encl->srcu);
 
-	list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+	list_for_each_entry_srcu(encl_mm, &encl->mm_list, list,
+			srcu_read_lock_held(&encl->srcu)) {
 		if (!mmget_not_zero(encl_mm->mm))
 			continue;
 
@@ -1018,7 +1020,8 @@ static struct mem_cgroup *sgx_encl_get_mem_cgroup(struct sgx_encl *encl)
 	 */
 	idx = srcu_read_lock(&encl->srcu);
 
-	list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+	list_for_each_entry_srcu(encl_mm, &encl->mm_list, list,
+			srcu_read_lock_held(&encl->srcu)) {
 		if (!mmget_not_zero(encl_mm->mm))
 			continue;
 
@@ -1212,7 +1215,8 @@ void sgx_zap_enclave_ptes(struct sgx_encl *encl, unsigned long addr)
 
 		idx = srcu_read_lock(&encl->srcu);
 
-		list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+		list_for_each_entry_srcu(encl_mm, &encl->mm_list, list,
+				srcu_read_lock_held(&encl->srcu)) {
 			if (!mmget_not_zero(encl_mm->mm))
 				continue;
 
diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
index 38b7fd2..581e0c4 100644
--- a/arch/x86/kernel/cpu/sgx/main.c
+++ b/arch/x86/kernel/cpu/sgx/main.c
@@ -120,7 +120,8 @@ static bool sgx_reclaimer_age(struct sgx_epc_page *epc_page)
 
 	idx = srcu_read_lock(&encl->srcu);
 
-	list_for_each_entry_rcu(encl_mm, &encl->mm_list, list) {
+	list_for_each_entry_srcu(encl_mm, &encl->mm_list, list,
+			srcu_read_lock_held(&encl->srcu)) {
 		if (!mmget_not_zero(encl_mm->mm))
 			continue;
 
-- 
2.9.4