Re: [Xen-devel] query on physical memory map for Xen?

["Peter Teoh" <htmldeveloper@xxxxxxxxx>]

Just curious, can anyone give a hint on where this 16GB max physical
memory is defined?

Doing some random search by strings I found these:

#define MAXMEM           0x3fffffffffffUL
#define MAXMEM                  (__FIXADDR_TOP-__PAGE_OFFSET-__VMALLOC_RESERVE)
#define MAXMEM_PFN      PFN_DOWN(MAXMEM)
#define ACPI_MEM_LIST_MAX               6
#define NR_NODE_MEMBLKS (MAX_NUMNODES*2)
#define EFI_MAX_MEMORY_TYPE             14
#define  PCI_X_CMD_MAX_READ     0x000c  /* Max Memory Read Byte Count */
#define  PCI_X_STATUS_MAX_READ  0x00600000      /* Designed Max Memory
Read Count */
#define GEO_TYPE_MAX            (GEO_TYPE_MEM+1)
#define NR_NODE_MEMBLKS (MAX_NUMNODES*2)
    *max_mfn = xc_memory_op(xc_handle, XENMEM_maximum_ram_page, NULL);
#define EFI_MAX_MEMORY_TYPE             14
#define MAXMEM           0x3fffffffffffUL
 * KEXEC_SOURCE_MEMORY_LIMIT maximum page get_free_page can return.
#define MAXMEM                  (__FIXADDR_TOP-__PAGE_OFFSET-__VMALLOC_RESERVE)
#define MAXMEM_PFN      PFN_DOWN(MAXMEM)
 * KEXEC_SOURCE_MEMORY_LIMIT maximum page get_free_page can return.
#define ACPI_MEM_LIST_MAX               6
#define XENMEM_maximum_ram_page     2
#define XENMEM_maximum_reservation  4
#define XENMEM_maximum_gpfn         14
#define NR_NODE_MEMBLKS (MAX_NUMNODES*2)
#define EFI_MAX_MEMORY_TYPE             14
#define GEO_TYPE_MAX            (GEO_TYPE_MEM+1)
#define NR_NODE_MEMBLKS (MAX_NUMNODES*2)

Not sure which one maps to this 16GB thing?   Thanks for the sharing :-).

On Fri, Apr 11, 2008 at 2:54 PM, Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:
> On 11/4/08 07:14, "pradeep singh rautela" <rautelap@xxxxxxxxx> wrote:
>
>  > Based on my understanding of the Xen code, I have a small query for you 
> all.
>  >
>  > Xen hypervisor can access only a max of 16GB of physical memory
>  > directly on x86 architecture.
>  > Is this correct inference?
>  >
>  > So does Xen hypervisor cannot touch memory about 16G directly? Does it
>  > employ some kind of temporary mapping like linux kernel to access
>  > memory above 16G then?
>
>  32-bit Xen does not use memory above 16GB at all. 64-bit Xen can use any
>  amount of memory, and is able to keep a permanent mapping of all of it.
>
>   -- Keir
>
>
>
>
>
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>



-- 
Regards,
Peter Teoh

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