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 22:52, Jonathan Tripathy wrote:
> On 28/08/2012 22:50, Jonathan Tripathy wrote:
>>
>>
>> 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
>>
> Ooops, typo'd the code (I had to recreate the changes as I deleted my 
> source tree). Here is the version I used:
>
> 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;
>     }
>     else 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");
>     }
>
>
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Anyway, question is moot. I rebuilt my code using your ordering of the 
if block and it works just fine. All 32GB is detected. I actually agree 
with your order because as you as, 801 is outdated.