Re: Can't see more than 3.5GB of RAM / UEFI / no e820 memory map detected

[Jonathan Tripathy <jonnyt@abpni.co.uk>]

On 28/08/2012 22:41, Keir Fraser wrote:
> On 28/08/2012 22:13, "Jonathan Tripathy" <jonnyt@abpni.co.uk> wrote:
>
>> Keir Fraser wrote:
>>> On 28/08/2012 20:36, "Jonathan Tripathy" <jonnyt@abpni.co.uk> wrote:
>>>
>>>>>> Thanks for the clarification.
>>>>>>
>>>>>> So from a security/reliability standpoint, nothing will be affected by
>>>>>> flipping the if block?
>>>>> It should simply make it more likely that Xen sees all your RAM. ;)
>>>>>
>>>>>     -- Keir
>>>>>
>>>>>
>>>> Hi Everyone,
>>>>
>>>> I reversed the if block in setup.c and now my server can see the full
>>>> 32GB of RAM. I haven't submitted a patch yet as we have run into another
>>>> (possibly unrelated to xen) issue with this server build that we are
>>>> working on. Once we complete our full testing, a patch will be submitted :)
>>> In this case, I will re-make the patch myself and check it in. Since it is a
>>> trivial one.
>>>
>>>     Thanks,
>>>    Keir
>> Thanks Keir
> Now done. xen-unstable:25786
>
>   -- Keir
Hi Keir,

Thanks for doing that. However, the ordering of the if block in my code 
that I used was slightly different from your commit. Perhaps this 
doesn't make too much of a difference?

Thanks

if ( mbi->flags & MBI_MEMMAP )
     {
         memmap_type = "Multiboot-e820";
         while ( (bytes < mbi->mmap_length) && (e820_raw_nr < E820MAX) )
         {
             memory_map_t *map = __va(mbi->mmap_addr + bytes);

             /*
              * This is a gross workaround for a BIOS bug. Some 
bootloaders do
              * not write e820 map entries into pre-zeroed memory. This is
              * okay if the BIOS fills in all fields of the map entry, but
              * some broken BIOSes do not bother to write the high word of
              * the length field if the length is smaller than 4GB. We
              * detect and fix this by flagging sections below 4GB that
              * appear to be larger than 4GB in size.
              */
             if ( (map->base_addr_high == 0) && (map->length_high != 0) )
             {
                 if ( !e820_warn )
                 {
                     printk("WARNING: Buggy e820 map detected and fixed "
                            "(truncated length fields).\n");
                     e820_warn = 1;
                 }
                 map->length_high = 0;
             }

             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_raw_nr++;

             bytes += map->size + 4;
         }
     }
     else if ( mbi->flags & MBI_MEMLIMITS )
     {
         memmap_type = "Multiboot-e801";
         e820_raw[0].addr = 0;
         e820_raw[0].size = mbi->mem_lower << 10;
         e820_raw[0].type = E820_RAM;
         e820_raw[1].addr = 0x100000;
         e820_raw[1].size = mbi->mem_upper << 10;
         e820_raw[1].type = E820_RAM;
         e820_raw_nr = 2;
     }
     if ( e820_raw_nr != 0 )
     {
         memmap_type = "Xen-e820";
     }
     else if ( bootsym(lowmem_kb) )
     {
         memmap_type = "Xen-e801";
         e820_raw[0].addr = 0;
         e820_raw[0].size = bootsym(lowmem_kb) << 10;
         e820_raw[0].type = E820_RAM;
         e820_raw[1].addr = 0x100000;
         e820_raw[1].size = bootsym(highmem_kb) << 10;
         e820_raw[1].type = E820_RAM;
         e820_raw_nr = 2;
     }
     else
     {
         EARLY_FAIL("Bootloader provided no memory information.\n");
     }