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

[LIU Wei <liuw@xxxxxxxxx>]

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
  cmd_line:
  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
c1079000(1079000)-0(c2000000)".
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.

LIU Wei

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