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[Xen-devel] Mini-OS as dom0, init_mm questions

  • To: xen-devel@xxxxxxxxxxxxxxxxxxx
  • From: LIU Wei <liuw@xxxxxxxxx>
  • Date: Tue, 27 Oct 2009 21:18:34 +0800
  • Delivery-date: Tue, 27 Oct 2009 07:53:09 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>

Hi, Xen experts,

We are doing some development with xen-3.3.0 . We plan to use Mini-OS as a
trusted computing base and boot it in the first place.

We have removed all Xenstore/Console reference in Mini-OS, since there will not
be Xenstore or console at that time. And we moved its virtual address
base to 0xc0000000
Then something strange happened within /* init_mm() */ .

I specified /* dom0_mem=32M */ , and got following message.

Xen Minimal OS!
start_info:   c1062000
  nr_pages:   8192  shared_inf: 001e9000
  pt_base:    c1063000  mod_start:  0xc004a000
  mod_len:    16842752
  flags:      0x3
  stack:      c0029460-c0049460
MM: Init
  _text:        c0000000
  _etext:       c001a104
  _erodata:     c001f000
  _edata:       c001f2f0
  stack start:  c0029460
  _end:         c0049910
  start_pfn:    1075
  max_pfn:      2000
Mapping memory range 0xc1800000 - 0xc2000000
setting c0000000-c001f000 readonly
skipped c0001000
MM: Initialise page allocator for c1079000(1079000)-0(c2000000)
Page fault at linear address c1400008, eip c000ceee, regs c003ff08, sp
0000107a, our_sp c003fef0, code 2
Page fault in pagetable walk (access to invalid memory?).

Notice the 3rd line to the last, "Initialise page allocator for
According to source code, last physical address of that line should be
2000000, not c2000000, and
corresponding virtual address should be c2000000, not 0. How could
this possibly go wrong? I am confused.

There is another problem with page fault. The 2nd line to the last, PF
at linear address c1400008. I thought
that VA should have been mapped correctly, because /*
build_pagetable() */ didn't complain anything. I
checked /* physical_to_machine */ array, found a mapping between that
VA and machine frame.

By the way, if I use this Mini-OS image as a domU, it should boot up properly.

Does anybody know any thing about those issues? I'm looking forward to
your reply.

Thanks in advanced.


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