Re: Hyp compat_memory_op() and 256 GB PV

[Mukesh Rathor <mukesh.rathor@oracle.com>]

Keir Fraser wrote:
 > On 18/02/2009 03:39, "Mukesh Rathor" <mukesh.rathor@oracle.com> wrote:
 >
 >> Moving on to 256 GB guest, the hyp is failing the XENMEM_populate_physmap
 >> hcall in compat_memory_op(). The problem is size too large for continuation
 >> encoding:
 >>
 >>      /* Is size too large for us to encode a continuation? */
 >>      if ( cmp.rsrv.nr_extents > (UINT_MAX >> MEMOP_EXTENT_SHIFT))
 >>          return start_extent;
 >>
 >>       for 256 GB : nr_extents == 0x4000000
 >>
 >>   Currently at a loss on this one!
 >
 > Well, who's making the compat call? Not the guest itself presumably since it
 > is 64-bit? So it's probably dom0? But I would think that dom0 would only do
 > large amounts of allocation for the new domU in xc_hvm_build.c, and that is
 > careful to allocate memory in batches of 8MB at a time.
 >
 > Basically you need to track down the call site of the failed
 > compat_memory_op().
 >
 >  -- Keir
 >

Hi Keir,

I see this in domain-builder-ng.log:

elf_xen_addr_calc_check: addresses:
     virt_base        = 0xffffffff80000000
     elf_paddr_offset = 0xffffffff80000000
     virt_offset      = 0x0
     virt_kstart      = 0xffffffff80200000
     virt_kend        = 0xffffffff807014e4
     virt_entry       = 0xffffffff80200000
xc_dom_parse_elf_kernel: xen-3.0-x86_64: 0xffffffff80200000 ->
0xffffffff807014e4
xc_dom_mem_init: mem 262144 MB, pages 0x4000000 pages, 4k each
xc_dom_mem_init: 0x4000000 pages
xc_dom_boot_mem_init: called
x86_compat: guest xen-3.0-x86_64, address size 64
xc_dom_malloc            : 256 MB
xc_dom_boot.c:143: panic: xc_dom_boot_mem_init: can't allocate low
memory for domain


I set a breakpoint in compat_memory_op() and stepping thru it, noticed
it was bailing out at the if statement, and nr_extents was 0x4000000.

This is a PV domain BTW, I guess xc_hvm_build.c wont' be involved. I'll
instrument libxc and debug more... meanwhile I thought I'd post this.

Thanks,
Mukesh