On Fri, 2022-03-18 at 14:27 -0300, Jason Gunthorpe wrote:
> Following the pattern of io_uring, perf, skb, and bpf iommfd will use
iommufd ----^
> 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.
Since this will replace parts of vfio this difference seems
significant. Can you explain this a bit more?
I'm also a bit confused how io_uring handles this. When I stumbled over
the problem fixed by 6b7898eb180d ("io_uring: fix imbalanced sqo_mm
accounting") and from that commit description I seem to rember that
io_uring also accounts in mm->locked_vm too? In fact I stumbled over
that because the wrong accounting in io_uring exhausted the applied to
vfio (I was using a QEMU utilizing io_uring itself).
>
> Signed-off-by: Jason Gunthorpe <[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 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)
> {
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