Re: [PATCH v19 5/8] mm: introduce memfd_secret system call to create "secret" memory areas

[David Hildenbrand]

On 18.05.21 11:59, Michal Hocko wrote:
> On Sun 16-05-21 10:29:24, Mike Rapoport wrote:
> > On Fri, May 14, 2021 at 11:25:43AM +0200, David Hildenbrand wrote:
> [...]
> > > > +		if (!page)
> > > > +			return VM_FAULT_OOM;
> > > > +
> > > > +		err = set_direct_map_invalid_noflush(page, 1);
> > > > +		if (err) {
> > > > +			put_page(page);
> > > > +			return vmf_error(err);
> > >
> > > Would we want to translate that to a proper VM_FAULT_..., which would most
> > > probably be VM_FAULT_OOM when we fail to allocate a pagetable?
> >
> > That's what vmf_error does, it translates -ESOMETHING to VM_FAULT_XYZ.
>
> I haven't read through the rest but this has just caught my attention.
> Is it really reasonable to trigger the oom killer when you cannot
> invalidate the direct mapping. From a quick look at the code it is quite
> unlikely to se ENOMEM from that path (it allocates small pages) but this
> can become quite sublte over time. Shouldn't this simply SIGBUS if it
> cannot manipulate the direct mapping regardless of the underlying reason
> for that?

OTOH, it means our kernel zones are depleted, so we'd better reclaim 
somehow ...

--
Thanks,

David / dhildenb