Re: [PATCH 1/4] mm: abstract initial stack setup to mm subsystem

[Lorenzo Stoakes]

On Thu, Apr 24, 2025 at 05:55:20PM -0700, Suren Baghdasaryan wrote:
> On Thu, Apr 24, 2025 at 2:30 PM David Hildenbrand <david@xxxxxxxxxx> wrote:
> >
> > On 24.04.25 23:15, Lorenzo Stoakes wrote:
> > > There are peculiarities within the kernel where what is very clearly mm
> > > code is performed elsewhere arbitrarily.
> > >
> > > This violates separation of concerns and makes it harder to refactor code
> > > to make changes to how fundamental initialisation and operation of mm logic
> > > is performed.
> > >
> > > One such case is the creation of the VMA containing the initial stack upon
> > > execve()'ing a new process. This is currently performed in __bprm_mm_init()
> > > in fs/exec.c.
> > >
> > > Abstract this operation to create_init_stack_vma(). This allows us to limit
> > > use of vma allocation and free code to fork and mm only.
> > >
> > > We previously did the same for the step at which we relocate the initial
> > > stack VMA downwards via relocate_vma_down(), now we move the initial VMA
> > > establishment too.
> > >
> > > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@xxxxxxxxxx>
> > > ---
> > ...
> >
> > > +/*
> > > + * Establish the stack VMA in an execve'd process, located temporarily at the
> > > + * maximum stack address provided by the architecture.
> > > + *
> > > + * We later relocate this downwards in relocate_vma_down().
> > > + *
> > > + * This function is almost certainly NOT what you want for anything other than
> > > + * early executable initialisation.
> > > + *
> > > + * On success, returns 0 and sets *vmap to the stack VMA and *top_mem_p to the
> > > + * maximum addressable location in the stack (that is capable of storing a
> > > + * system word of data).
> > > + *
> > > + * on failure, returns an error code.
>
> nit: s/on/On
> You could also skip this sentence altogether since it's kinda obvious
> but up to you.

Ack, and yeah probably best to just drop tbh :)

>
> > > + */
> >
> > I was about to say, if you already write that much documentation, why
> > not turn it into kerneldoc? :) But this function is clearly not intended
> > to have more than one caller, so ... :)
> >
> > Acked-by: David Hildenbrand <david@xxxxxxxxxx>
>
> Reviewed-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
>
> >
> > --
> > Cheers,
> >
> > David / dhildenb
> >