Re: [RFC PATCH 4/6] mm/memory: Add tree limit to free_pgtables()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Sep 04, 2025 at 12:20:55PM +0200, David Hildenbrand wrote:
> On 03.09.25 22:19, Liam R. Howlett wrote:
> > * Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [250819 15:14]:
> > > On Fri, Aug 15, 2025 at 03:10:29PM -0400, Liam R. Howlett wrote:
> > > > The ceiling and tree search limit need to be different arguments for the
> > > > future change in the failed fork attempt.
> > > >
> > > > No functional changes intended.
> > > >
> > > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> > >
> > > (Obv. in addition to comment about broken VMA tests :P)
> > >
> > > I guess intent is that if we discover any page tables beyond tree_max then
> > > we ought to just wipe them all out so, in effect, we don't consider
> > > mappings at or past tree_max to be valid?
> >
> > Actually... there are some archs that map outside the vma and they are
> > valid.. I think mips? and I think lower, but yeah.. it's needed.  This
> > is why prev->vm_end and next->vm_start are used as page table limits,
> > afaik.  This is a serious annoyance because it frequently adds walks
> > that are infrequently necessary to the vma tree.
>
> Hm, does that still exist?
>
> I recall something odd ... was it that gate area thingy (in_gate_area) we
> also have to handle in GUP code? The is x86/arm though, not mips.

Isn't gate area the VSYSCALL area so that's basically a kernel mapping address
that we allow userland to access?

>
> --
> Cheers
>
> David / dhildenb
>