linux-kernel - [PATCH] kdump x86: fix total mem size calculation for reservation

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Date:	Fri, 9 Mar 2012 16:30:09 +0800
From:	Dave Young <dyoung@...hat.com>
To:	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux@....linux.org.uk, vgoyal@...hat.com
Subject: [PATCH] kdump x86: fix total mem size calculation for reservation

crashkernel reservation need know the total memory size. Current get_total_mem
simply use max_pfn - min_low_pfn. It is wrong because it will including
memory holes in the middle.

Especially for kvm guest with memory > 0xe0000000, there's below in qemu code:
qemu split memory as below:
    if (ram_size >= 0xe0000000 ) {
        above_4g_mem_size = ram_size - 0xe0000000;
        below_4g_mem_size = 0xe0000000;
    } else {
        below_4g_mem_size = ram_size;
    }
So for 4G mem guest, seabios will insert a 512M usable region beyond of 4G.
Thus in above case max_pfn - min_low_pfn will be more than original memsize.

Fixing this issue by using memblock_phys_mem_size() to get the total memsize.

Signed-off-by: Dave Young <dyoung@...hat.com>
---
 [Ther's similar code in arm, I'm not sure whether the memblock_phys_mem_size
 works with arm or not. If it works I can also update that part of code.]
 arch/x86/kernel/setup.c |   12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

--- linux-2.6.orig/arch/x86/kernel/setup.c	2012-03-09 11:27:30.000000000 +0800
+++ linux-2.6/arch/x86/kernel/setup.c	2012-03-09 15:41:29.666530976 +0800
@@ -509,16 +509,6 @@ static void __init memblock_x86_reserve_
 
 #ifdef CONFIG_KEXEC
 
-static inline unsigned long long get_total_mem(void)
-{
-	unsigned long long total;
-
-	total = max_pfn - min_low_pfn;
-	printk("hidave: memsize=%llu\n", memblock_phys_mem_size());
-
-	return total << PAGE_SHIFT;
-}
-
 /*
  * Keep the crash kernel below this limit.  On 32 bits earlier kernels
  * would limit the kernel to the low 512 MiB due to mapping restrictions.
@@ -537,7 +527,7 @@ static void __init reserve_crashkernel(v
 	unsigned long long crash_size, crash_base;
 	int ret;
 
-	total_mem = get_total_mem();
+	total_mem = memblock_phys_mem_size();
 
 	ret = parse_crashkernel(boot_command_line, total_mem,
 			&crash_size, &crash_base);
--
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