Re: [PATCH v6 07/19] kernel/user: Allow user::locked_vm to be usable for iommufd

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Nov 29, 2022 at 04:29:30PM -0400, Jason Gunthorpe wrote:
> 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.
> 
> Tested-by: Nicolin Chen <nicolinc@nvidia.com>
> Tested-by: Yi Liu <yi.l.liu@intel.com>
> Tested-by: Lixiao Yang <lixiao.yang@intel.com>
> Tested-by: Matthew Rosato <mjrosato@linux.ibm.com>
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Reviewed-by: Eric Auger <eric.auger@redhat.com>
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

Just curious: why does the subject say "user::locked_vm"? As opposed to
user->locked_vm? Made me think it's somehow related to rust in kernel or
whatever.

> ---
>  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 f054d0360a7533..4cc52698e214e2 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 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)
>  {
> -- 
> 2.38.1