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

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Date:   Thu, 3 Aug 2017 15:12:59 +0800
From:   Wei Yang <richard.weiyang@...il.com>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/mm: trivial code cleanup for memory_map_top_doown()

Hmm.... ping...

On Tue, May 2, 2017 at 9:26 PM, Wei Yang <richard.weiyang@...il.com> wrote:
> Hi, Borislav and all
>
> Do you agree with my analysis or you have other comments?
>
> On Tue, Mar 14, 2017 at 11:56:39AM +0800, Wei Yang wrote:
>>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
>>Help you, Help me
>
>
>
> --
> Wei Yang
> Help you, Help me