2017-03-13 18:50:48

by Borislav Petkov

[permalink] [raw]
Subject: Re: [PATCH] x86/mm: trivial code cleanup for memory_map_top_doown()

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

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
@@ -506,10 +506,14 @@ static void __init memory_map_top_down(unsigned long map_start,
unsigned long addr;
unsigned long mapped_ram_size = 0;

+ pr_info("%s: entry, [0x%lx:0x%lx)\n", __func__, map_start, map_end);
+
/* xen has big range in reserved near end of ram, skip it at first.*/
addr = memblock_find_in_range(map_start, map_end, PMD_SIZE, PMD_SIZE);
real_end = addr + PMD_SIZE;

+ pr_info("%s: addr: 0x%lx, real_end: 0x%lx\n", __func__, addr, real_end);
+
/* step_size need to be small so pgt_buf from BRK could cover it */
step_size = PMD_SIZE;
max_pfn_mapped = 0; /* will get exact value next */
@@ -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);
+
start = map_start;
+ }
+
mapped_ram_size += init_range_memory_mapping(start,
last_start);
last_start = start;

--
Regards/Gruss,
Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.


2017-03-14 03:56:45

by Wei Yang

[permalink] [raw]
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
Help you, Help me


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2017-03-20 02:26:25

by Wei Yang

[permalink] [raw]
Subject: Re: [PATCH] x86/mm: trivial code cleanup for memory_map_top_doown()

Hi, Borislav

Do you still have some concern on this change?

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


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