linux-kernel - Re: [PATCH] x86/mm: trivial code cleanup for memory_map_top

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Date:   Tue, 14 Mar 2017 11:56:39 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Wei Yang <richard.weiyang@...il.com>, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/mm: trivial code cleanup for memory_map_top_doown()

On Mon, Mar 13, 2017 at 07:50:21PM +0100, Borislav Petkov wrote:
>On Fri, Feb 17, 2017 at 10:30:33PM +0800, Wei Yang wrote:
>> In case (last_start <= step_size), start is for sure to be 0. So, it is
>

Hmm, I may write it more specific:

"start" is for sure to be set to 0 with round_down(last_start - 1, step_size).

>Well, lemme see:
>
>[    0.000000] memory_map_top_down: entry, [0x100000:0x7ffdf000)
>[    0.000000] memory_map_top_down: addr: 0x7fc00000, real_end: 0x7fe00000
>[    0.000000] memory_map_top_down: last_start: 0x40000000 <= step_size: 0x2000000000, start: 0x40000000
>											      ^^^^^^^^^^
>It doesn't look like 0 to me.
>
>---
>diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
>index 2193799ca800..d3b02a416df3 100644
>--- a/arch/x86/mm/init.c
>+++ b/arch/x86/mm/init.c
>@@ -527,8 +531,13 @@ static void __init memory_map_top_down(unsigned long map_start,
> 			start = round_down(last_start - 1, step_size);
> 			if (start < map_start)
> 				start = map_start;
>-		} else
>+		} else {
>+			pr_info("%s: last_start: 0x%lx <= step_size: 0x%lx, start: 0x%lx\n",
>+				__func__, last_start, step_size, start);
>+

If you change this log with the following

			pr_err("%s: last_start: 0x%lx <= step_size: 0x%lx, start: 0x%lx\n",
				__func__, last_start, step_size,
				round_down(last_start - 1, step_size));

You could see after calculation, start is 0 when (last_start <= step_size).

-- 
Wei Yang
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