linux-kernel - Re: [PATCH -v2 13/13] x86, 64bit: Map first 1M ram early before memblock_x86

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Message-ID: <CAOJsxLFtpBnvtA3F=7NDJunqXRs4AL1=oe7HR6GECgGfr9TqDA@mail.gmail.com>
Date:	Mon, 3 Sep 2012 08:50:01 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...e.hu>,
	"H. Peter Anvin" <hpa@...or.com>, Jacob Shin <jacob.shin@....com>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -v2 13/13] x86, 64bit: Map first 1M ram early before memblock_x86_fill()

On Sun, Sep 2, 2012 at 10:46 AM, Yinghai Lu <yinghai@...nel.org> wrote:
> This one intend to fix bugs:
> when efi booting have too many memmap entries, will need to double memblock
> memory array or reserved array.

Okay, why do we need to do that?

> +RESERVE_BRK(early_pgt_alloc, 65536);

What is this needed for?

> +void  __init early_init_mem_mapping(void)
> +{
> +       unsigned long tables;
> +       phys_addr_t base;
> +       unsigned long start = 0, end = ISA_END_ADDRESS;
> +
> +       probe_page_size_mask();
> +
> +       if (max_pfn_mapped)
> +               return;

I find this confusing - what is this protecting for? Why is
'max_pfn_mapped' set when someone calls early_init_mem_mappings()?

Side note: we have multiple "pfn_mapped" globals and it's not at all
obvious to me what the semantics for them are. Maybe adding a comment
or two in arch/x86/include/asm/page_types.h would help.

> +
> +       tables = calculate_table_space_size(start, end);
> +       base = __pa(extend_brk(tables, PAGE_SIZE));
> +
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