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

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Date:   Mon, 13 Mar 2017 19:50:21 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Wei Yang <richard.weiyang@...il.com>
Cc:     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 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.

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