Re: [Qemu-devel] BIOS checksums?

[Piotr Krysik]

--- Gianni Tedesco <address@hidden> wrote:
> On Mon, 2004-06-21 at 15:10 -0700, Piotr Krysik
> wrote:
> > 2. Memory
> > 
> > I have to reserve some memory for QEMU. I'm
> > allocating some MB of top of RAM. The rest is
> > visible to guest OS with it's real address
> > (addresses used by emulated CPU is identical
> > to addresses used by hardware), so it should
> > be possible to use DMA without translating
> > addresses. Also I don't have to treat memory
> > mapped hardware in any special way.
> 
> How is e820 map obtained, would it be possible to
> intercept that to
> setup a new reserved area I wonder? ;)
> 
> An uglier approach would be adding to the e820 map
> which is presumably
> stored in the ROM, and fixup the checksum...

It should be possible to modify op_raise_interrupt to
handle int15/e820 as a special case for emulated CPU.
I didn't implement it yet. For my Linux exercise with
Bochs BIOS I just modified CMOS-stored memory size.
BIOS did the rest:-)


> > The QEMU area is not visible to emulated CPU, so
> > it's protected from direct access by guest OS.
> > It could be accessed by DMA (e.g. broken drivers).
> > If such (unlikely) case is discovered, it can be
> > handled by intercepting and modifying IO or memory
> > access used to setup that DMA.
> > 
> > To run BIOS, I had to intercept some IO that tried
> > to reprogram RAM Controller.
> 
> Is this because of the way you reserve RAM?

Yes.

In QEMU, the emulated CPU does direct access only to
memory registered with cpu_register_physical_memory.
The rest of CPU address space is handled by
unassigned_mem_read/unassigned_mem_write functions
(with exception of regions registered with
cpu_register_io_memory).

For the prototype I register RAM area allocated to
guest OS with cpu_register_physical_memory(0,
guest_ram_size, 0). The rest of CPU address space is
handled by unassigned_mem_read/unassigned_mem_write.
In these functions I forward memory access to the real
machine (after checking that it doesn't overlap with
the emulator).


> So when do we see the patches? ;))

At this point it's just quick and dirty prototype not
ready for public release. And I don't expect to reach
release quality any time soon. As it matures I'd like
to release it under GPL (it depends only on libqemu,
so I'm not limited to GPL).


> > BTW. What is "PMC config space"? Did you mean DIMM
> > Serial Presence Detect?
> 
> In the PCI configuration space of the PCI controller
> itself (0:0.0) are
> contained registers such as:
> 
>  DRAM Row Type
>  DRAM Control
>  DRAM Timing
>  DRAM Row Boundary
>  Fixed DRAM Hole Control
>  SMRAM Control
> 
> But as I see now, these values are programmed in to
> the PMC by the BIOS,
> duh.

Yes. And I had to intercept and emulate these
registers, because at the point BIOS started
reprogramming PMC I lost control over emulator.


Regards,

Piotrek



                
__________________________________
Do you Yahoo!?
New and Improved Yahoo! Mail - Send 10MB messages!
http://promotions.yahoo.com/new_mail