RE: [Xen-devel] [PATCH] Increasing E820MAX

["Nakajima, Jun" <jun.nakajima@xxxxxxxxx>]

Ian Pratt wrote:
> This breaks x86_64 boot! It crashes in the Xen ACPI code.
> 
> Ian
I don't see the problem on machine that I typically use, but I found and
fixed the problem on a big machine. It was causing a stack overflow. If
you look at the current code, it's a bit dangerous, see => part. This
patch fixes it.

+static struct e820entry e820_raw[E820MAX];
+
 void __init __start_xen(multiboot_info_t *mbi)
 {
     char *cmdline;
@@ -253,7 +255,6 @@
     unsigned long _initrd_start = 0, _initrd_len = 0;
     unsigned int initrdidx = 1;
     physaddr_t s, e;
-    struct e820entry e820_raw[E820MAX];
     int i, e820_raw_nr = 0, bytes = 0;
     struct ns16550_defaults ns16550 = {
         .data_bits = 8,


----
    if ( mbi->flags & MBI_MEMMAP )
    {
        while ( bytes < mbi->mmap_length )
        {
            memory_map_t *map = __va(mbi->mmap_addr + bytes);
        =>    e820_raw[e820_raw_nr].addr = 
                ((u64)map->base_addr_high << 32) |
(u64)map->base_addr_low;
        =>    e820_raw[e820_raw_nr].size = 
                ((u64)map->length_high << 32) | (u64)map->length_low;
        =>    e820_raw[e820_raw_nr].type = 
                (map->type > E820_SHARED_PAGE) ? E820_RESERVED :
map->type;
        =>    e820_raw_nr++;
            bytes += map->size + 4;
        }
    }


> 
>> We found machines with >32 E820 memory map entries, where Xen
>> fails to boot (but Linux does boot fine). The native Linux
>> (both x86 and x86_86) already has:
>> 
>> #define E820MAX      128             /* number of entries in
>> E820MAP */
>> 
>> Signed-off-by: Jun Nakajima <jun.nakajima@xxxxxxxxx>
>> 
>> Jun
>> ---
>> Intel Open Source Technology Center
>> 
>> --
>> diff -r 3bb1857981e6 -r 51e9c0c806b2 xen/include/asm-x86/e820.h
>> --- a/xen/include/asm-x86/e820.h     Tue Aug 16 19:38:22 2005
>> +++ b/xen/include/asm-x86/e820.h     Wed Aug 17 17:00:29 2005 @@ -3,7
>> +3,7 @@ 
>> 
>>  #include <asm/page.h>
>> 
>> -#define E820MAX     32
>> +#define E820MAX     128
>> 
>>  #define E820_RAM          1
>>  #define E820_RESERVED     2



Jun
---
Intel Open Source Technology Center

e820_stack.patch
Description: e820_stack.patch

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