[PATCH RFC 04/12] kernel/user: Allow user::locked_vm to be usable for iommufd

[Jason Gunthorpe <jgg@nvidia.com>]

Following the pattern of io_uring, perf, skb, and bpf iommfd will use
user->locked_vm for accounting pinned pages. Ensure the value is included
in the struct and export free_uid() as iommufd is modular.

user->locked_vm is the correct accounting to use for ulimit because it is
per-user, and the ulimit is not supposed to be per-process. Other
places (vfio, vdpa and infiniband) have used mm->pinned_vm and/or
mm->locked_vm for accounting pinned pages, but this is only per-process
and inconsistent with the majority of the kernel.

Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
---
 include/linux/sched/user.h | 2 +-
 kernel/user.c              | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/user.h b/include/linux/sched/user.h
index 00ed419dd46413..c47dae71dad3c8 100644
--- a/include/linux/sched/user.h
+++ b/include/linux/sched/user.h
@@ -24,7 +24,7 @@ struct user_struct {
 	kuid_t uid;
 
 #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
-    defined(CONFIG_NET) || defined(CONFIG_IO_URING)
+    defined(CONFIG_NET) || defined(CONFIG_IO_URING) || IS_ENABLED(CONFIG_IOMMUFD)
 	atomic_long_t locked_vm;
 #endif
 #ifdef CONFIG_WATCH_QUEUE
diff --git a/kernel/user.c b/kernel/user.c
index e2cf8c22b539a7..d667debeafd609 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -185,6 +185,7 @@ void free_uid(struct user_struct *up)
 	if (refcount_dec_and_lock_irqsave(&up->__count, &uidhash_lock, &flags))
 		free_user(up, flags);
 }
+EXPORT_SYMBOL_GPL(free_uid);
 
 struct user_struct *alloc_uid(kuid_t uid)
 {
-- 
2.35.1