Re: Protected mode transitions and big real mode... still an issue

[Laurent Vivier <Laurent.Vivier@bull.net>]

Le mardi 29 avril 2008 à 19:09 +0200, Laurent Vivier a écrit :
> Le mardi 29 avril 2008 à 11:41 -0500, Anthony Liguori a écrit :
> > Guillaume Thouvenin wrote:
> > > Hello,
> > >
> > >  This patch should solve the problem observed during protected mode
> > > transitions that appears for example during the installation of
> > > openSuse-10.3. Unfortunately there is an issue that crashes
> > > kvm-userspace. I'm not sure if it's a problem introduced by the
> > > patch or if the patch is good and raises a new issue.
> > >   
> > 
> > You still aren't emulating the instructions correctly I think.  Running 
> > your patch, I see:
> > 
> > [  979.755349] Failed vm entry (exit reason 0x21) invalid guest state
> > [  979.755354] emulation at (46e4b) rip 6e0b: ea 10 6e 18
> > [  979.755358] successfully emulated instruction
> > [  979.756105] Failed vm entry (exit reason 0x21) invalid guest state
> > [  979.756109] emulation at (46e50) rip 6e10: 66 b8 20 00
> > [  979.756111] successfully emulated instruction
> > [  979.756749] Failed vm entry (exit reason 0x21) invalid guest state
> > [  979.756752] emulation at (46e54) rip 6e14: 8e d8 8c d0
> > [  979.756755] successfully emulated instruction
> > [  979.757427] Failed vm entry (exit reason 0x21) invalid guest state
> > [  979.757430] emulation at (46e56) rip 6e16: 8c d0 81 e4
> > [  979.757433] successfully emulated instruction
> > [  979.758074] Failed vm entry (exit reason 0x21) invalid guest state
> > [  979.758077] emulation at (46e58) rip 6e18: 81 e4 ff ff
> > 
> > 
> > The corresponding gfxboot code is:
> > 
> >  16301 00006E0B EA[106E]1800                    jmp 
> > pm_seg.prog_c32:switch_to_pm_20
> >  16302                                  switch_to_pm_20:
> >  16303                                 
> >  16304                                          bits 32
> >  16305                                 
> >  16306 00006E10 66B82000                        mov ax,pm_seg.prog_d16
> >  16307 00006E14 8ED8                            mov ds,ax
> >  16308                                 
> >  16309 00006E16 8CD0                            mov eax,ss
> >  16310 00006E18 81E4FFFF0000                    and esp,0ffffh
> >  
> > 
> > The VT state should be correct after executing instruction an RIP 6E16 
> > (mov eax, ss).  The next instruction should not cause a vmentry 
> 
> Are you sure ? It is intel notation (opcode dst,src) , so it updates
> eax, not ss. Guillaumes gives us (with gdb notation, opcode src,dst):
> 
>   0x0000000000046e53:  ljmp   $0x18,$0x6e18
> 
>   0x0000000000046e58:  mov    $0x20,%ax
> 
> %EAX = 0x20
> 
>   0x0000000000046e5c:  mov    %eax,%ds
> 
> %DS = 0x20
> 
>   0x0000000000046e5e:  mov    %ss,%eax
> 
> %EAX = %SS = 0x53E1 (in this particular case)
> 
> For me the issue is with instructions with "dst.byte = 0".
> for instance:
> 
> 0x0000000000046e66:  shl    $0x4,%eax
> 
> [82768.003174] emulation at (46e66) rip 6e26: c1 e0 04 01
> [82768.035153]     writeback: dst.byte 0
> [82768.055174]     writeback: dst.ptr  0x0000000000000000
> [82768.087177]     writeback: dst.val  0x53e1
> [82768.111178]     writeback: src.ptr  0x0000000000006e28
> [82768.143157]     writeback: src.val  0x4
> 
> So my questions are:
> 
> Why dst.val is not 0x53e10 ?

I can answer myself to this one:

	emulate_2op_SrcB("sal", c->src, c->dst, ctxt->eflags);

does nothing if dst.byte == 0

So next question is the good question...

> Why dst.byte is 0 ?
> 
> > failure.  The fact that it is for you indicates that you're not updating 
> > guest state correctly.
> > 
> > My guess would be that load_segment_descriptor is not updating the 
> > values within the VMCS.
> > 
> > Regards,
> > 
> > Anthony Liguori
> 
> Regards
> Laurent
-- 
------------- Laurent.Vivier@bull.net ---------------
"The best way to predict the future is to invent it."
- Alan Kay


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