Re: [RFC] Porting KVM to QEMU CVS

[Anthony Liguori <aliguori-NZpS4cJIG2HvQtjrzfazuQ@public.gmane.org>]

Avi Kivity wrote:
>>
>>> 2. Add hacks in the memory slot code to not return a memory slot if 
>>> the physical address is in the forbidden range.
>>
>> I'm not sure I understand what you mean by this.  I guess I have to 
>> spend some time and understand how the whole memory slot thing works.
>
> Memory slots are just like the DIMM (or, since the qemu model is 
> rather old, SIMM) slots in a PC.
>
> A PC memory controller has circuitry to route memory access to a DIMM 
> or to the PCI bus.  The logic is something like this (first match wins):
>
> - if the access is to the VGA hole, and we're not in SMM, route the 
> access to PCI (the vga controller will route it further to somewhere 
> in the framebuffer)
> - if the access is to the VGA hole, and we are in SMM mode, route to 
> the DIMM that contains the address
> - if the access is to the ROM areas (0xf0000-0xfffff), route to the ROM
> - if the access is to an area mapped by a DIMM, do that
> - otherwise it's an mmio access
>
> My proposal is to implement the special runtime routing table. This 
> way we can have a DIMM that covers all of memory including the 
> forbidden hole.

Okay, that makes sense.

> Entry into SMM will issue an ioctl() to remove the vga routing; exit 
> from SMM will reinstall it.

Right.

>> Another option to consider would simply be to have the BIOS detect 
>> whether or not the emulated hardware supports SMM dynamically (right 
>> now, it's a compile time switch).  This would let us turn it off in 
>> QEMU when KVM is enabled.
>>
>
> That may be best.  What does SMM buy us anyway?

I was hoping to be able to do this with something like CPUID but there 
isn't a bit.  Right now I'm using PIO but I'd have to ask on the bochs 
mailing list whether or not this is a reasonable thing to do.

The current bochs bios doesn't really do anything with SMM.  It merely 
enables or disables ACPI.

Regards,

Anthony Liguori

>
>>>
>>>> Is anyone else working on this?
>>>
>>> I intended to merge qemu once a release is made.  However, if you 
>>> get this working and it is stable, it may make sense to merge sooner 
>>> as I very much like qemu cvs.
>>
>> I would rather just submit this patch (with the BIOS hack) to QEMU 
>> and try and get it picked up in CVS.  There are some regressions at 
>> the moment in CVS so it may be nice for users to have an 0.8.2 based 
>> version available. What do you think?
>>
>> Would be nice to have KVM support in QEMU CVS by the time 2.6.20 
>> rolls out.
>
> I'll reply to this in the next email, this one's too long already.
>


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