Re: [PATCH v3 2/4] mm: Make generic arch_is_kernel_initmem_freed() do what it says

[Christophe Leroy]

Le 04/11/2021 à 22:44, Andrew Morton a écrit :
> On Fri, 01 Oct 2021 17:14:41 +1000 Daniel Axtens <dja@xxxxxxxxxx> wrote:
>
> > >   #ifdef __KERNEL__
> > > +/*
> > > + * Check if an address is part of freed initmem. After initmem is freed,
> > > + * memory can be allocated from it, and such allocations would then have
> > > + * addresses within the range [_stext, _end].
> > > + */
> > > +#ifndef arch_is_kernel_initmem_freed
> > > +static int arch_is_kernel_initmem_freed(unsigned long addr)
> > > +{
> > > +	if (system_state < SYSTEM_FREEING_INITMEM)
> > > +		return 0;
> > > +
> > > +	return init_section_contains((void *)addr, 1);
> >
> > Is init_section_contains sufficient here?
> >
> > include/asm-generic/sections.h says:
> >   * [__init_begin, __init_end]: contains .init.* sections, but .init.text.*
> >   *                   may be out of this range on some architectures.
> >   * [_sinittext, _einittext]: contains .init.text.* sections
> >
> > init_section_contains only checks __init_*:
> > static inline bool init_section_contains(void *virt, size_t size)
> > {
> > 	return memory_contains(__init_begin, __init_end, virt, size);
> > }
> >
> > Do we need to check against _sinittext and _einittext?
> >
> > Your proposed generic code will work for powerpc and s390 because those
> > archs only test against __init_* anyway. I don't know if any platform
> > actually does place .init.text outside of __init_begin=>__init_end, but
> > the comment seems to suggest that they could.
>
> Christophe?

Sorry for answering late.

I've been thorugh free_initmem() in each architecture. The only sections 
involved in the freeing actions are [__init_begin, __init_end], so I 
think checking against __init_being, __init_end is enough.

If some architecture has init text outside of this section, then it is 
not freed hence not necessary to check.

Christophe