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SubjectRe: [PATCH 1/5] vfio/type1: use pinned_vm instead of locked_vm to account pinned pages
On Mon, Feb 11, 2019 at 03:56:20PM -0700, Jason Gunthorpe wrote:
> On Mon, Feb 11, 2019 at 05:44:33PM -0500, Daniel Jordan wrote:
> > @@ -266,24 +267,15 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
> > if (!mm)
> > return -ESRCH; /* process exited */
> >
> > - ret = down_write_killable(&mm->mmap_sem);
> > - if (!ret) {
> > - if (npage > 0) {
> > - if (!dma->lock_cap) {
> > - unsigned long limit;
> > -
> > - limit = task_rlimit(dma->task,
> > - RLIMIT_MEMLOCK) >> PAGE_SHIFT;
> > + pinned_vm = atomic64_add_return(npage, &mm->pinned_vm);
> >
> > - if (mm->locked_vm + npage > limit)
> > - ret = -ENOMEM;
> > - }
> > + if (npage > 0 && !dma->lock_cap) {
> > + unsigned long limit = task_rlimit(dma->task, RLIMIT_MEMLOCK) >>
> > +
> > - PAGE_SHIFT;
>
> I haven't looked at this super closely, but how does this stuff work?
>
> do_mlock doesn't touch pinned_vm, and this doesn't touch locked_vm...
>
> Shouldn't all this be 'if (locked_vm + pinned_vm < RLIMIT_MEMLOCK)' ?
>
> Otherwise MEMLOCK is really doubled..

So this has been a problem for some time, but it's not as easy as adding them
together, see [1][2] for a start.

The locked_vm/pinned_vm issue definitely needs fixing, but all this series is
trying to do is account to the right counter.

Daniel

[1] http://lkml.kernel.org/r/20130523104154.GA23650@twins.programming.kicks-ass.net
[2] http://lkml.kernel.org/r/20130524140114.GK23650@twins.programming.kicks-ass.net

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