Re: [PATCH v3 1/5] kernel/user: Allow user _struct::locked_vm to be usable for iommufd

On 17 August 2026 22:24:00 BST, Bradley Morgan <[email protected]> wrote:
>On 17 August 2026 21:16:02 BST, Farhan Ali <[email protected]> wrote:
>>From: Jason Gunthorpe <[email protected]>
>>
>>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 good accounting to use for ulimit because it is
>>per-user, and the security sandboxing of locked pages 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 new FOLL_LONGTERM users in
>>the kernel.
>>
>>Concurrent work is underway to try to put this in a cgroup, so everything
>>can be consistent and the kernel can provide a FOLL_LONGTERM limit that
>>actually provides security.
>>
>>Link:
>https://lore.kernel.org/r/[email protected]
>>Reviewed-by: Kevin Tian <[email protected]>
>>Reviewed-by: Eric Auger <[email protected]>
>
>Reviewed-by: Bradley Morgan <[email protected]> # kernel/
>

Oopsie! I didn't realise it was a backport commit :(

Could you add [PATCH 6.1.x] or something in the title, so I don't mess up
again

>>Tested-by: Nicolin Chen <[email protected]>
>>Tested-by: Yi Liu <[email protected]>
>>Tested-by: Lixiao Yang <[email protected]>
>>Tested-by: Matthew Rosato <[email protected]>
>>Signed-off-by: Jason Gunthorpe <[email protected]>
>>(cherry picked from commit ce5a23c835aa0f0a931b5bcde1e7811f951b0146)
>>Signed-off-by: Farhan Ali <[email protected]>
>>---
>> 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 f054d0360a75..4cc52698e214 100644
>>--- a/include/linux/sched/user.h
>>+++ b/include/linux/sched/user.h
>>@@ -25,7 +25,7 @@ struct user_struct {
>> 
>> #if defined(CONFIG_PERF_EVENTS) || defined(CONFIG_BPF_SYSCALL) || \
>> 	defined(CONFIG_NET) || defined(CONFIG_IO_URING) || \
>>-	defined(CONFIG_VFIO_PCI_ZDEV_KVM)
>>+	defined(CONFIG_VFIO_PCI_ZDEV_KVM) || 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 e2cf8c22b539..d667debeafd6 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)
>> {
>>
>
>
>Thanks!

Thanks!