linux-kernel - Re: [PATCH v3 2/4] mm: Make generic arch_is_kernel_initmem

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Message-Id: <20211104144442.7130ae4a104fca70623a2d1a@linux-foundation.org>
Date:   Thu, 4 Nov 2021 14:44:42 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Daniel Axtens <dja@...ens.net>
Cc:     Christophe Leroy <christophe.leroy@...roup.eu>, arnd@...db.de,
        linux-arch@...r.kernel.org, linux-s390@...r.kernel.org,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 2/4] mm: Make generic arch_is_kernel_initmem_freed()
 do what it says

On Fri, 01 Oct 2021 17:14:41 +1000 Daniel Axtens <dja@...ens.net> 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?