Re: Problem with KVM guest switching to x86 long mode

[Avi Kivity <avi@redhat.com>]

On 04/11/2010 09:30 AM, Pekka Enberg wrote:
> Avi Kivity wrote:
>> The instruction at 0x28 is enabling paging, next insn fetch faults, 
>> so the paging structures must be incorrect.
>>
>> Questions:
>> - what is the u64 at cr3? (call it pte4)
>> - what is the u64 at (pte4 & ~0xfff)?  (call it pte3)
>> - what is the u64 at (pte3 & ~0xfff)? ("pte2")
>> - what is the u64 at ((pte2 & ~0xfff) + 2048)? ("pte1")
>>
>> Note if bit 7 of pte2 is set, then pte1 is unneeded.
>
> Sorry for the delay. Here you go:
>
> Page Tables:
>  pte4: 0000000002403007   pte3: 0000000002404007   pte2: 0000000000000183

These are all correct.

The only thing I can think of, is that MAXPHYADDR is small value.  And 
indeed, if I run it on an ept capable machine (which does the check in 
hardware, not software), I get

IO error: OUT port=cf8, size=4, count=1
KVM exit reason: 2 ("KVM_EXIT_IO")
Registers:
  rip: ffffffff813a0d8f   rsp: ffffffff8167bdf8 flags: 0000000000000086
  rax: 000000008000c300   rbx: 000000000000c000   rcx: 0000000000000000
  rdx: 0000000000000cf8   rsi: 0000000000000018   rdi: 0000000000000000
  rbp: ffffffff8167be08   r8:  0000000000000000   r9:  0000000000000000
  r10: 0000000000000006   r11: 00000000bbceeb20   r12: 0000000000000000
  r13: 0000000000000000   r14: 0000000000000000   r15: 0000000000000000
  cr0: 0000000080050033   cr2: 0000000000000000   cr3: 0000000001001000
  cr4: 00000000000000a0   cr8: 0000000000000000

So the guest is in long mode, happily trying to access pci config space.

MAXPHYADDR comes from cpuid 80000008.eax[0:7].  Typical values are 36-40 
(number of physical address bits supported by the processor).  What 
value does your guest see?

-- 
error compiling committee.c: too many arguments to function